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Dr. Eng. Ion SMARANDA

Scientific Researcher III

Laboratory of Optical Processes in Nanostructured Materials

ion[DOT]smaranda[AT]infim[DOT]ro

Education

2013-2018 - PhD in physics, Faculty of Physics, University of Bucharest, department of Optics, Spectroscopy, Plasma, Lasers;

2009-2011 -  Master Degree in Optics, Spectroscopy, Plasma and Laser, University of Bucharest, Faculty of Physics, Department of Physics;

2004-2009 - Engineer’s Degree, Technological Physics, University of Bucharest, Faculty of Physics.

Positions

03/2023 - present : Scientific research 3rd degree, National Institute of Materials Physics Măgurele in Optical Processes in Nanostructured Materials Laboratory

12/2018 - 02/2023 : Scientific research, National Institute of Materials Physics Măgurele in Optical Processes in Nanostructured Materials Laboratory

2010 - 2018: Research Assistant, National Institute of Materials Physics Măgurele in Optical Processes in Nanostructured Materials Laboratory

Expertize

Skills and abilities:  Photoluminescence; UV-VIS-NIR absorption spectroscopy; Raman scattering; FT-IR spectroscopy; dielectric spectroscopy, cyclic voltammetry;

Patents

C.M. Manta, D. Samohvalov, D. Gherca, M. Baibarac, M. A. Lungan, I. Smaranda, A. Barbatu, L. Buhalteanu, A. Udrescu, M. Daescu, M. Ilie, N. Toulbe, Procedures for the preparation and use of the new crystalline forms of 6-(3-methyl-5-nitroimidazol-4-yl)sulfanyl-9H-purine, patent application no. A/00516/28.08.2019.

Publications

1. Physico-chemical properties of two anhydrous azathioprine forms and their interaction with typical pharmaceutical excipients: highlighting new findings in drug formulation development
Authors: Barbatu, A; Lungan, MA; Toulbe, N; Smaranda, I; Daescu, M; Baibarac, M; Manta, CM

Published: FEB 2022, DRUG DEVELOPMENT AND INDUSTRIAL PHARMACY, DOI: 10.1080/03639045.2022.2032131

The physico-chemical properties of two anhydrous AZA forms and their interaction with typical pharmaceutical excipients were assessed by applying various methods (such as PXRD, HPLC, TG/DSC, IR, Raman, PL or UV-Vis) in order to highlight new directions for drug formulation. The stability assessment of AZA anhydrous forms I and II was performed in order to determine the risk of degradation of the active ingredient by accidental exposure to nonstandard conditions in the industrial environment, under different storage, transport or processing conditions. The benefits of form II include increased resistance to chemical degradation over a wide range of pH, but further control of storage and processing conditions is necessary to avoid polymorphic transformation into form I. The solubility assessment on the AZA solid forms in different environments that simulate the conditions of the gastrointestinal tract has the advantage of a significantly increased solubility of form II compared with the commercial form I due to the modification of the crystalline structure. In the case of capsules compared to AZA form I or II as powder, an improvement in their solubility was observed, promoted by the presence of one or more excipients in the formulation mixture.
2. The Photoluminescence and Vibrational Properties of Black Phosphorous Sheets Chemically/Electrochemically Functionalized in the Presence of Diphenylamine
Authors: Baibarac, M., Burlanescu, T., Stroe, M., Smaranda, I., & Negrila, C.

Published: NOV 2022, Polymers, 21, 4479, DOI: 10.3390/polym14214479

In this work, new information concerning the optical properties of black phosphorus (BP) sheets chemically/electrochemically functionalized with diphenyl amine (DPA) and its macromolecular compound (poly(diphenylamine) (PDPA)) in the absence/presence of phosphotungstic acid (PTA) is reported. Raman scattering and FTIR spectroscopy studies indicate that the interaction of BP with PTA leads to the elimination of the PxOy layer onto the surface of the BP sheets. In the case of the chemical interaction of BP with DPA, the reaction product corresponds to DPA chemically functionalized BP sheets having an imino-phosphorane (IP) structure. The electrochemical oxidation of BP sheets chemically functionalized with DPA in the presence of PTA leads to an increase in the weight of P-N bonds as a consequence of the generation of PDPA doped with the PTA heteropolyanions, as shown by FTIR spectroscopy and Raman scattering. This process is evidenced by a shift of the Raman line from 362 cm(-1) to 378 cm(-1), assigned to the A(1g) mode. This change was explained by taking into account the compression of the layers containing P atoms, which is induced by PDPA macromolecular chains. The decrease in the intensity of the PL spectra of DPA as well as PDPA, in the presence of BP, indicates that BP acts as a PL quenching agent for these compounds. A preferential orientation of the PDPA doped with the PTA heteropolyanions on the surface of BP sheets is highlighted by the variation of the binding angle of the PDPA on the surface of BP sheets from 44.7 degrees to 39.9 degrees.
3. Degradation of Losartan Potassium Highlighted by Correlated Studies of Photoluminescence, Infrared Absorption Spectroscopy and Dielectric Spectroscopy
Authors: Paraschiv, M; Smaranda, I; Zgura, I; Ganea, P; Chivu, M; Chiricuta, B; Baibarac, M

Published: NOV 2022, PHARMACEUTICS , 14, 2419, DOI: 10.3390/pharmaceutics14112419

In this paper, new results on the degradation of losartan potassium (LP, (1)), in the absence and presence of excipients, which was induced by UV light, the acid character of phosphate buffer solution (PBS) and alkaline medium, respectively, are reported through correlated studies of FTIR spectroscopy, photoluminescence and dielectric spectroscopy. The photoluminescence (PL) spectra of LP and the drug marked under the name Lorista (LO) are characterized by intense emission bands, peaking at 378 nm and 380 nm, respectively, accompanied by low intensity bands with a maximum at similar to 450-460 nm. Photodegradation of LO in a solid state is evidenced by a decrease in the intensity of the PL band at 380 nm, a variation that originates both in the adsorption of water vapors from the air and in the interaction of LP with excipients such as cornstarch, silicon dioxide and cellulose. The LP-water interaction is described, taking into account the main electrical parameters, i.e., complex dielectric permittivity and electrical conductivity. Photodegradation of LP and LO also induces an increase in the intensity of the emission band, at similar to 450-460 nm. The influence of acid and alkaline medium on the LO degradation is analyzed using phosphate buffer (PBS) and NaOH solutions, respectively. In both cases, a decrease in the intensity of the PL band, at 380 nm, is reported. The intensity diminution of the PL spectra of NaOH-reacted LP and LO is the result of the formation of the photodegradation product N-methanolamide-{[2\'-(1H-tetrazol-5-yl)(1,1\'-biphenyl)-4-yl]methyl} (2). This compound was proven by the studies of FTIR spectroscopy achieved on LP and NaOH-reacted LP. The appearance of the IR band at 1740 cm(-1) and the increase in the absorbance in the IR band at 1423 cm(-1) indicate that the photodegradation product (2) contains the C=O and C-OH functional groups.
4. Correlated studies of photoluminescence, vibrational spectroscopy and mass spectrometry concerning the pantoprazole sodium photodegradation
Authors: Baibarac, M; Paraschiv, M; Cercel, R; Smaranda, I; Bartha, C; Trandabat, A

Published: JUN 9 2022, SCIENTIFIC REPORTS, 12, 9515, DOI: 10.1038/s41598-022-13648-6

In this work, new optical evidences concerning the changes induced of the UV light on pantoprazole sodium (PS), in solid state and as aqueous solution, are reported by UV-VIS spectroscopy, photoluminescence (PL), Raman scattering and FTIR spectroscopy. New evidences concerning the products of the PS photodegradation pathways are reported by the correlated studies of thermogravimetry and mass spectrometry. The influence of the excipients and alkaline medium on the PS photodegradation is also studied. New aspects regarding the chemical mechanism of the PS photodegradation in the presence of the water vapor and oxygen form air and the alkaline medium are shown. Our results confirm that the PS photodegradation induced of the water vapors and oxygen from air leads to the generation of 5-difluoromethoxy-3H-benzimidazole-2-thione sodium, 5-difluoromethoxy-3H-benzimidazole sodium, 2-thiol methyl-3, 4-dimethoxypyridine and 2-hydroxymethyl-3, 4-dimethoxypyridine, while in the alkaline medium, compounds of the type of the 2-oxymethyl-3,4-dimethoxypyridine sodium salts are resulted.
5. New superdielectric materials: (1-x) SrFe12O19 - x BNT-BT nanocomposites
Authors: Greculeasa, SG; Comanescu, C; Iacob, N; Kuncser, A; Smaranda, I; Amarande, L; Cioangher, M; Burdusel, M; Teodorescu, V

Published: OCT 1 2022, PHYSICA B-CONDENSED MATTER, 642, 414139, DOI: 10.1016/j.physb.2022.414139

Novel (1-x) SrFe12O19 - x BNT-BT0.08 (x = 0; 0.5; 0.8; 1) nanocomposites were explored in this study. The samples were produced by sol-gel method and compacted by conventional sintering. The composition, morphology, local structure, dielectric and magnetic properties were investigated by X-ray diffraction, Transmission Electron Microscopy, Impedance Analysis, Mossbauer spectroscopy, and SQUID magnetometry. The desired composition and the presence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. Irregular morphology and large size distributions are evidenced in the electron microscopy micrographs. The reported room temperature dielectric constants in this study are the highest values obtained in multiferroic composites at room temperature: giant dielectric constants (similar to 1.3 x 10(6)) were obtained, relative to 0.13 x 10(4) in BNT-BT. The hyperfine parameters allowed the identification of the Wyckoff positions of the Fe ions corresponding closely to the theoretical case. The hard magnetic character of the SrFe12O19 phase is evidenced from the magnetic measurements. For the first time in multifermic composites, superdielectric characteristics are evidenced at room temperature.
6. Photodegradation of Azathioprine in the Presence of Sodium Thiosulfate
Authors: Toulbe, N; Smaranda, I; Negrila, C; Bartha, C; Manta, CM; Baibarac, M

Published: APR 2022, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 23, 3975, DOI: 10.3390/ijms23073975

The effect of sodium thiosulfate (ST) on the photodegradation of azathioprine (AZA) was analyzed by UV-VIS spectroscopy, photoluminescence (PL), FTIR spectroscopy, Raman scattering, X-ray photoelectron (XPS) spectroscopy, thermogravimetry (TG) and mass spectrometry (MS). The PL studies highlighted that as the ST concentration increased from 25 wt.% to 75 wt.% in the AZA:ST mixture, the emission band of AZA gradual downshifted to 553, 542 and 530 nm. The photodegradation process of AZA:ST induced: (i) the emergence of a new band in the 320-400 nm range in the UV-VIS spectra of AZA and (ii) a change in the intensity ratio of the photoluminescence excitation (PLE) bands in the 280-335 and 335-430 nm spectral ranges. These changes suggest the emergence of new compounds during the photo-oxidation reaction of AZA with ST. The invoked photodegradation compounds were confirmed by studies of the Raman scattering, the FTIR spectroscopy and XPS spectroscopy through: (i) the downshift of the IR band of AZA from 1336 cm(-1) to 1331 cm(-1), attributed to N-C-N deformation in the purine ring; (ii) the change in the intensity ratio of the Raman lines peaking at 1305 cm(-1) and 1330 cm(-1) from 3.45 to 4.57, as the weight of ST in the AZA:ST mixture mass increased; and (iii) the emergence of a new band in the XPS O1s spectrum peaking at 531 eV, which was associated with the C=O bond. Through correlated studies of TG-MS, the main key fragments of ST-reacted AZA are reported.
7. Optical, Structural, and Dielectric Properties of Composites Based on Thermoplastic Polymers of the Polyolefin and Polyurethane Type and BaTiO3 Nanoparticles
Authors: Baibarac, M; Nila, A; Smaranda, I; Stroe, M; Stingescu, L; Cristea, M; Cercel, RC; Lorinczi, A; Ganea, P; Mercioniu, I; Ciobanu, R; Schreiner, C; Garcia, RG; Bartha, C

Published: FEB 2021, MATERIALS, 14, DOI: 10.3390/ma14040753

In this work, new films containing composite materials based on blends of thermoplastic polymers of the polyurethane (TPU) and polyolefin (TPO) type, in the absence and presence of BaTiO3 nanoparticles (NPs) with the size smaller 100 nm, were prepared. The vibrational properties of the free films depending on the weight ratio of the two thermoplastic polymers were studied. Our results demonstrate that these films are optically active, with strong, broad, and adjustable photoluminescence by varying the amount of TPU. The crystalline structure of BaTiO3 and the influence of thermoplastic polymers on the crystallization process of these inorganic NPs were determined by X-ray diffraction (XRD) studies. The vibrational changes induced in the thermoplastic polymer's matrix of the BaTiO3 NPs were showcased by Raman scattering and FTIR spectroscopy. The incorporation of BaTiO3 NPs in the matrix of thermoplastic elastomers revealed the shift dependence of the photoluminescence (PL) band depending on the BaTiO3 NP concentration, which was capable of covering a wide visible spectral range. The dependencies of the dielectric relaxation phenomena with the weight of BaTiO3 NPs in thermoplastic polymers blends were also demonstrated.
8. The Influence of the Ceramic Nanoparticles on the Thermoplastic Polymers Matrix: Their Structural, Optical, and Conductive Properties
Authors: Smaranda, I; Nila, A; Ganea, P; Daescu, M; Zgura, I; Ciobanu, RC; Trandabat, A; Baibarac, M

Published: AUG 2021, POLYMERS, 13, DOI: 10.3390/polym13162773

This paper prepared composites under the free membranes form that are based on thermoplastic polymers of the type of polyurethane (TPU) and polyolefin (TPO), which are blended in the weight ratio of 2:1, and ceramic nanoparticles (CNs) such as BaSrTiO3 and SrTiO3. The structural, optical, and conductive properties of these new composite materials are reported. The X-ray diffraction studies highlight a cubic crystalline structure of these CNs. The main variations in the vibrational properties of the TPU:TPO blend induced by CNs consist of the following: (i) the increase in the intensity of the Raman line of 1616 cm(-1); (ii) the down-shift of the IR band from 800 to 791 cm(-1); (iii) the change of the ratio between the absorbance of IR bands localized in the spectral range 950-1200 cm(-1); and (iv) the decrease in the absorbance of the IR band from 1221 cm(-1). All these variations were correlated with a preferential adsorption of thermoplastic polymers on the CNs surface. A photoluminescence (PL) quenching process of thermoplastic polymers is demonstrated to occur in the presence of CNs. The anisotropic PL measurements have highlighted a change in the angle of the binding of the TPU:TPO blend, which varies from 23.7 degrees to approximate to 49.3 degrees and approximate to 53.4 degrees, when the concentration of BaSrTiO3 and SrTiO3 CNs, respectively, is changed from 0 to 25 wt. %. Using dielectric spectroscopy, two mechanisms are invoked to take place in the case of the composites based on TPU:TPO blends and CNs, i.e., one regarding the type of the electrical conduction and another specifying the dielectric-dipolar relaxation processes.
9. Vibrational and Photoluminescence Properties of Composites Based on Double-Walled Carbon Nanotubes, Poly(o-phenylenediamine) and Poly(ethylene oxide)
Authors: Daescu, M; Oprica, M; Smaranda, I; Matei, E; Nastac, D; Cramariuc, O; Cramariuc, B; Baibarac, M

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18975

Chemical polymerization of o-phenylenediamine (OPD) in the presence of poly(ethylene oxide), double-wall carbon nanotubes (DWNTs) and ferric chloride is carried out in order to obtain composites based on the poly(o-phenylenediamine)-poly(ethylene oxide) (POPD-PEO) fibres covered and interconnected with DWNTs. Vibrational and photoluminescence properties of these composite materials as well as their morphologies are shown by infrared (IR) spectroscopy, Raman scattering, photoluminescence (PL) and scanning electron microscopy (SEM). An adsorption of DWNTs onto the POPD rods surface in the absence and in the presence of. PEO is highlighted by SEM. The vibrational changes reported by Raman scattering and IR spectroscopy prove a covalent functionalization of DWNTs with the macromolecular compound POPD which is doped with FeCl4- T ions. New hydrogen bonds are generated between POPD covalently functionalized DWNTs and hydroxyl groups of PEO according to IR spectroscopic studies. The two macromolecular compounds, POPD and POPD-PEO, show a complex emission band with maxima at 572 and 566 nm, having a shoulder at 667 nm. A significant change in the profile of the PL bands of POPD and POPD-PEO is induced in the DWNTs presence. We show that DWNTs induce (i) a diminution in the POPD PL band intensity peaked between 525-600 nm simultaneous with the increase in the intensity of the PL band situated in the 600-800 nm spectral range and (ii) an enhancement process of the emission band localized in the 475-800 nm spectral range in the case of POPD-PEO.
10. Physico-chemical properties of two anhydrous azathioprine forms and their interaction with typical pharmaceutical excipients: highlighting new findings in drug formulation development
Authors: Barbatu, A; Lungan, MA; Toulbe, N; Smaranda, I; Daescu, M; Baibarac, M; Manta, CM

Published: OCT 3 2021, DRUG DEVELOPMENT AND INDUSTRIAL PHARMACY, 47, DOI: 10.1080/03639045.2022.2032131

The physico-chemical properties of two anhydrous AZA forms and their interaction with typical pharmaceutical excipients were assessed by applying various methods (such as PXRD, HPLC, TG/DSC, IR, Raman, PL or UV-Vis) in order to highlight new directions for drug formulation. The stability assessment of AZA anhydrous forms I and II was performed in order to determine the risk of degradation of the active ingredient by accidental exposure to nonstandard conditions in the industrial environment, under different storage, transport or processing conditions. The benefits of form II include increased resistance to chemical degradation over a wide range of pH, but further control of storage and processing conditions is necessary to avoid polymorphic transformation into form I. The solubility assessment on the AZA solid forms in different environments that simulate the conditions of the gastrointestinal tract has the advantage of a significantly increased solubility of form II compared with the commercial form I due to the modification of the crystalline structure. In the case of capsules compared to AZA form I or II as powder, an improvement in their solubility was observed, promoted by the presence of one or more excipients in the formulation mixture.
11. UV Light Effect on Cationic Photopolymerization of the SU8 Photoresist and Its Composites with Carbon Nanotubes: New Evidence Shown by Photoluminescence Studies
Authors: Baibarac, M; Radu, A.; Cristea, M; Cercel, R; Smaranda, I

Published: APR 2 2020, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 7476, DOI: 10.1021/acs.jpcc.9b11925

The effect of UV light on the cationic photopolymerization of the SU8 negative photoresist is shown by photoluminescence (PL) studies. Our results demonstrate that the cationic photopolymerization reaction of the SU8 photoresist takes place predominantly under the influence of the UVA light. Using UVA light, the influence of carbon nanotubes [of the types single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs), multiwalled carbon nanotubes (MWNTs), and SWNTs functionalized with carboxyl groups (SWNTs-COOH)] on the cationic photopolymerization process of the SU8 photoresist is shown by PL studies. The cationic photopolymerization of the SU8 photoresist is monitored by the variations of the two emission bands with maxima at similar to 400-429 nm and 523-556 nm. The increase in the relative intensity of the PL band at similar to 523-556 nm is dependent on (i) the carbon nanotube concentration in the SU8 photoresist matrix; (ii) the type of carbon nanotubes, i.e., SWNTs, DWNTs, and MWNTs; and (iii) the nonfunctionalized and functionalized state of SWNTs. The results reported in this work demonstrate that PL can be used as a complementary method to Raman scattering and IR spectroscopy in the investigation of the cationic photopolymerization reaction of the SU8 negative photoresist. A decrease in the wrapping angle of carbon nanotubes with the SU8 photoresist is highlighted by anisotropic PL studies.
12. The influence of UV light on the azathioprine photodegradation: New evidences by photoluminescence
Authors: Smaranda, I; Nila, A; Manta, CM; Samohvalov, D; Gherca, D; Baibarac, M

Published: SEP 2019, RESULTS IN PHYSICS, 14, DOI: 10.1016/j.rinp.2019.102443

In this work, we report a photodegradation process of azathioprine (AZA) highlighted by correlated studies of photoluminescence (PL) and the UV-VIS and IR absorption spectroscopy. The photodegradation process of AZA is observed by the gradual increasing in the intensity of the PL spectrum recorded under the excitation wavelength of 300 nm. This behaviour is accompanied, in the photoluminescence excitation (PLE) spectra, by a gradual intensity decreasing of the PLE band situated in the 250-320 nm spectral range simultaneous with the intensity increasing of the PLE band localized in the 325-425 nm spectral range. Regardless if the immunosuppressive compound is in the state of powder, tablet or solution, the PL and UV-VIS absorption spectroscopy studies have demonstrated that a photodegradation process under UV light takes place. According to the PL studies carried out in ambient and vacuum condition, the photodegradation process of AZA was demonstrated to be influenced by the oxygen from air. The presence of a new IR band with maximum at 1745 cm(-1) confirms the AZA photodegradation pathway proposed in this work.
13. Photoluminescence and structural properties of the nitrogen doped TiO2 and the influence of SiO2 and Ag nanoparticles
Authors: Nila, A; Baibarac, M; Udrescu, A; Smaranda, I; Mateescu, A; Mateescu, G; Mereuta, P; Negrila, CC

Published: SEP 18 2019, JOURNAL OF PHYSICS-CONDENSED MATTER, 31, DOI: 10.1088/1361-648X/ab2692

Mixtures of nitrogen-doped titanium dioxide (TiO2:N) with different concentrations of Ag and/or SiO2 particles (0.5, 1 and 2 wt.%) were prepared in solid state by mechanico-chemical interactions. Using UV-VIS spectroscopy, Raman scattering, photoluminescence (PL) and photoluminescence excitation (PLE), the influence of the particles on the host material is evaluated. UV-VIS spectroscopy studies indicate a TiO2:N band gap shift to the UV range with increasing concentrations of SiO2 and Ag particles. PL intensities decrease with increasing concentrations of Ag and/or SiO2 particles in the TiO2:N host matrix, which in turn could effectively restrict the electron and hole recombination. To explain these processes, the different de-excitation ways will be advanced, taking into account the energy levels diagram of TiO2:N/Ag, TiO2:N/SiO2 and TiO2:N/Ag/SiO2 systems. PLE spectra show a gradual decrease in their relative intensities after 165 min of continuous irradiation due to photosensitivity of TiO2:N. The plasmonic effect of Ag particles in the TiO2:N/Ag system is highlighted for the first time by PLE studies.
14. Optical properties of folic acid in phosphate buffer solutions: the influence of pH and UV irradiation on the UV-VIS absorption spectra and photoluminescence
Authors: Baibarac, M; Smaranda, I; Nila, A; Serbschi, C

Published: OCT 3 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-50721-z

Using UV-VIS absorption spectroscopy, photoluminescence (PL) and photoluminescence excitation (PLE), the photodegradation reactions of folic acid (FA) in phosphate buffer (PB) solutions were studied. Regardless of the PB solution's pH, the UV-VIS spectra showed a gradual decrease in absorbance at 284 nm simultaneous with an increase in the absorbance of another band in the spectral range of 320-380 nm, which was downshifted under UV irradiation. The relative intensity of the FA PL band, situated in the spectral range 375-600 nm, was dependent on the pH of the PB solution. The FA PL intensity increased as increasing UV irradiation time up to 281 min. in PB solutions with pH values of 6.4 and 5.4. Under an emission wavelength of 500 nm, the position of the FA PLE spectrum changed as the PB solution pH varied from 7 to 5.4 and the irradiation time increased to 317 min. These changes were correlated with the formation of two photodegradation products, namely, pterine-6-carboxylic acid and p-amino-benzoyl-L-glutamic acid. According to UV-VIS spectroscopy and PL and PLE studies, the presence of various excipients in commercial pharmaceutical tablets does not affect the photodegradation of FA in PB solutions. Using IR spectroscopy, new evidences for the formation of the two photodegradation products of FA in PB solutions are shown.
15. The influence of single-walled carbon nanotubes on optical properties of the poly[(2,5-bisoctyloy)-1, 4-phenylenevinylene] evidenced by infrared spectroscopy and anti-Stokes photoluminescence
Authors: Baibarac, M; Smaranda, I; Baltog, I; Lefrant, S; Mevellec, JY

Published: MAY 2017, OPTICAL MATERIALS, 67, 58, DOI: 10.1016/j.optmat.2017.03.039

Significant differences are reported for the IR spectra of poly[(2,5-bisoctyloy)-1, 4-phenylenevinylene] (BO-PPV) recorded onto the KBr, Ag and Au supports. In this work, a decrease in the absorbance of the IR spectra of the BO-PPV films deposited onto Au and Ag supports as increasing the macromolecular compound film thickness is reported. A preferential orientation of the BO-PPV molecules and its composite with single-walled carbon nanotubes (SWNTs) versus metallic supports of Ag and Au is assessed using the IR absorption spectroscopy under s and p polarized light. An anti-Stokes photoluminescence (ASPL) is reported to characterize the BO-PPV macromolecular compound. The BO-PPV ASPL spectra intensity dependent both of the thickness of the macromolecular compound layer deposited onto the metallic supports and the SWNTs weight in the BO-PPV/SWNTs composite mass. (C) 2017 Elsevier B.V. All rights reserved.
16. Optical properties of single-walled carbon nanotubes functionalized with copolymer poly(3,4-ethylenedioxythiophene-co-pyrene)
Authors: Baltog, I; Baibarac, M; Smaranda, I; Matea, A; Ilie, M; Mevellec, JY; Lefrant, S

Published: DEC 2016, OPTICAL MATERIALS, 62, 611, DOI: 10.1016/j.optmat.2016.11.005

Optical properties are reported for composites based on single-walled carbon nanotubes (SWNT5) and copolymer poly(3,4-ethylenedioxythiophene-co-pyrene) (PEDOT-Py) prepared by chemical polymerization of two monomers in the presence of carbon nanotubes. A charge transfer between SWNT5 and the PEDOT-Py copolymer was demonstrated by Raman scattering. The increase in the relative intensity of the Raman lines peaked at 440-577 cm(-1), which were assigned to the ethylenedioxy ring vibrational modes, indicated a significant hindrance steric in the case of the composites based on the PEDOT-Py copolymer and metallic SWNTs. The increase in the absorbance of IR band peaked at 984 cm(-1) occurred simultaneously with the disappearance of the IR band at 1639 cm(-1). This finding was a consequence of the formation of new covalent bonds between SWNTs and the thiophene and benzene rings of the repeating units of the PEDOT-Py copolymer. The photoluminescence (PL) quenching process of the PEDOT-Py copolymer was induced by semiconducting SWNTs. The PL quenching of PEDOT-Py copolymer in the presence of SWNT5 was. demonstrated based on the energy level diagrams of the two constituents of the PEDOT-Py/SWNTs composite material. (C) 2016 Elsevier B.V. All rights reserved.
17. Photochemical processes developed in composite based on highly separated metallic and semiconducting SWCNTs functionalized with polydiphenylamine
Authors: Baibarac, M; Baltog, I; Smaranda, I; Magrez, A

Published: JAN 2015, CARBON, 81, 438, DOI: 10.1016/j.carbon.2014.09.075

The electrochemical polymerization of diphenylamine (DPA) onto electrodes of Pt coated with highly separated metallic (98%) or semiconducting (99%) single-walled carbon nanotubes (SWCNTs) in the presence of H3PW12O40 was performed by cyclic voltammetry in order to obtain composite materials based on polydiphenylamine (PDPA) doped with heteropolyanions of H3PW12O40 and carbon nanotubes. Our data demonstrate that the photoluminescence quenching effect of the PDPA doped with H3PW12O40 heteropolyanions in the presence of SWCNTs is due to the metallic component. Under UV irradiation of SWCNTs highly separated in metallic and semiconducting tubes functionalized with PDPA doped with heteropolyanions of H3PW12O40 new photochemical reactions are evidenced by photoluminescence studies. These reactions lead to a shortening of the macromolecular chain of PDPA. The photochemical process is more intense in the case semiconducting SWCNTs functionalized with PDPA doped with heteropolyanions in comparison to metallic SWCNTs functionalized with PDPA in doped state, it being a consequence of an additional chemical interaction between the DPA dimer doped with H3PW12O40 heteropolyanions and semiconducting SWCNTs. (C) 2014 Elsevier Ltd. All rights reserved.
18. Optical Properties of Single-Walled Carbon Nanotubes Functionalized with Poly(2,2 '-bithiophene-co-pyrene) Copolymer
Authors: Smaranda, I; Baibarac, M; Ilie, M; Matea, A; Baltog, I; Lefrant, S

Published: 2015, CURRENT ORGANIC CHEMISTRY, 19, 661, DOI: 10.2174/1385272819666150311231454

The photoluminescent (PL) properties of composites based on single-walled carbon nanotubes (SWNTs) and poly(2,2'-bithiophene-co-pyrene) (PBTh-Py), prepared by in situ chemical polymerization of the two monomers in the presence of carbon nanotubes, are reported. We demonstrate that the functionalization of SWNTs with PBTh-Py copolymer is revealed through a gradual quenching process of PL with the increase of SWNT content (semiconducting component) in the composite mass. FTIR spectroscopy indicates the existence of several steric hindrance effects that originate in the covalent functionalization of SWNTs with PBTh-Py copolymer. The film deposition of PBTh-Py copolymer and PBTh-Py/SWNTs composite onto rough Au supports induces changes in the FTIR spectrum, which originate in an adsorption mechanism caused by the preferential orientation of molecules on the metallic support. Surface-enhanced Raman scattering (SERS) spectroscopy reveals the side-wall functionalization of SWNTs with PBTh-Py copolymer by changes in the shapes, peak position and relative intensities of different Raman lines.
19. Exciton-phonon interaction in PbI2 revealed by Raman and photoluminescence studies using excitation light overlapping the fundamental absorption edge
Authors: Baibarac, M; Smaranda, I; Scocioreanu, M; Mitran, RA; Enculescu, M; Galatanu, M; Baltog, I

Published: OCT 2015, MATERIALS RESEARCH BULLETIN, 70, 772, DOI: 10.1016/j.materresbull.2015.06.012

Enhancement at low temperatures of the Raman scattering excited by laser light situated near the edge of the fundamental absorption band is often encountered when studying nanoscale structures. Theory devoted to this phenomenon has established that it originates in an exciton-phonon interaction process, known as the Frohlich interaction, Such a phenomenon was observed in PbI2. The experimental data conclude that the enhancement of the Raman emission results from: (i) an optical excitation near edge of fundamental absorption band; (ii) it is conditioned by the existence of excitonic PL; (iii) its occurrence is different over stokes and anti-stokes Raman branches as result of the different overlapping of the Raman spectral range and the excitonic PL band profile; and (iv) it appears more intense in micrometric powders or in bulk crystalline material. These data are interpreted as stimulated Raman effect resulting from the mixing of the pump laser light and the excitonic light. (C) 2015 Elsevier Ltd. All rights reserved.
20. Abnormal anti-Stokes Raman scattering and surface-enhanced infrared absorption spectroscopy studies of carbon nanotubes electrochemically functionalized with poly(2,2 '-bithiophene-co-pyrene)
Authors: Baibarac, M; Baltog, I; Smaranda, I; Scocioreanu, M; Mevellec, JY; Lefrant, S

Published: AUG 1 2014, APPLIED SURFACE SCIENCE, 309, 21, DOI: 10.1016/j.apsusc.2014.04.114

A new composite material was synthesized via the electrochemical oxidation of 2,2'-bithiophene (BTh) and pyrene (Py) monomers dissolved in a solution of LiC1O(4) in CH3CN onto a working electrode of Au coated with a film of single-walled carbon nanotubes (SWNTs). The interaction of the poly(2,2'-bithiophene-co-pyrene) (PBTh-Py) with the SWNTs and the orientation of the copolymer on the working electrode were studied by anti-Stokes and Stokes Raman scattering and FTIR spectroscopy in the grazing-incidence angle reflection geometry. The Raman lines at 1464 and 1435 cm(-1), attributed to the symmetric stretching modes of the C=C bond in the quinoid and aromatic rings of the PBTh-Py copolymer, were observed when the working electrode is either a blank Au film or a Au support coated with a SWNT film. In the latter case, charge transfer occurs at the interface of the two constituents. This charge transfer leads to functionalization of the carbon nanotubes with the copolymer molecules. The presence of enhanced anti-Stokes Raman lines at -1461, -1435 and -1187 cm(-1) indicates a resonant optical excitation process of the PBTh-Py/SWNT composite. The FTIR spectra acquired under polarized light for the PBTh-Py copolymer electrosynthesized on a bare Au support reveal significant changes in the absorption bands situated in the spectral ranges of 1000-1150 and 1550-1650 cm(-1) that originate in the surface-enhanced IR absorption (SEIRA) processes. The functionalization of the SWNTs with the PBTh-Py copolymer is evidenced by the enhancement of the absorption of the FTIR bands at 793 and 846 cm(-1), which are assigned to the C S C deformation vibrational mode and the substituted benzene ring, respectively, due to the effects of steric hindrance that are induced for the copolymer molecules by the binding of carbon nanotubes. (C) 2014 Elsevier B.V. All rights reserved.
21. Electrochemical Grafting of Reduced Graphene Oxide with Polydiphenylamine Doped with Heteropolyanions and Its Optical Properties
Authors: Smaranda, I; Benito, AM; Maser, WK; Baltog, I; Baibarac, M

Published: NOV 6 2014, JOURNAL OF PHYSICAL CHEMISTRY C, 118, 25717, DOI: 10.1021/jp507324r

Electropolymerization of diphenylamine (DPA) onto a reduced graphene oxide (RGO) film was carried out to obtain a corresponding RGO/polydiphenylamie (PDPA) composite doped with phosphotungstic acid (H3PW12O40) heteropolyanions (PT). The synthesis was performed in the absence of light, since UVvis spectroscopy and photoluminescence (PL) studies on RGO/DPA blends irradiated by UV light revealed a partial transformation of the DPA monomer into oligomers of PDPA. Raman scattering demonstrates that the electropolymerization of DPA in the presence of H3PW12O40 (PTA) and RGO leads to the formation of PDPA covalently bonded to the RGO sheets (RGO/PDPA:PT). The presence of heteropolyanions in the PDPA matrix (PDPA:PT) is detected by FTIR spectroscopy. Comparing the PL excitation spectra of PDPA:PT and the RGO/PDPA:PT composite highlights an upshift of the band gap that is accompanied by a change in the composition of the PL spectrum in the spectral range of 2.253.54 eV. These changes originate in a charge transfer that takes place at the interface of nongrafted RGO and PDPA:PT. The gradual increase of the PL intensity of RGO covalently grafted with PDPA:PT reveals photochemical reactions under UV irradiation. These involve the CC stretching vibrational mode in the benzene ring of PDPA and indicate the transformation of an RGO/PDPA:PT composite containing HPW12O402 anions into an RGO/PDPA:PT composite stabilized by PW12O403 anions. These results not only provide important insights on the interactions between RGO, conjugated polymers, and stabilizing dopant ions but also impact on the synthesis conditions.
22. Abnormal anti-Stokes Raman scattering and coherent backscattering as manifestation of Anderson localization of light in nonlinear mesoscopic materials
Authors: Smaranda, I; Mihut, L; Baibarac, M; Baltog, I; Lefrant, S

Published: SEP 2014, OPTICAL ENGINEERING, 53, DOI: 10.1117/1.OE.53.9.097109

We demonstrate that under continuous single-beam excitation, one can generate an abnormal antiStokes Raman emission (AASRE) whose properties are similar to a coherent anti-Stokes Raman scattering. The effect has been observed in mesoscopic materials, which possess intrinsically nonlinear properties [lithium niobate (LiNbO3), bismuth germanium oxide (Bi12GeO20; BGO), bismuth silicon oxide (Bi12GeO20; BSO)], which have a nonzero electric susceptibility of the third order, chi((3)) not equal 0. Corroborated Raman and coherent backscattering studies demonstrate that the occurrence of both effects is conditioned by the existence of a mesoscopic morphology of the sample, which is able to ensure efficient transport of the light inside the sample through a multiple light scattering mechanism. In this context, both AASRE and coherent backscattering effects are because of the Anderson localization of the light. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
23. Spectroelectrochemical properties of the poly[(2,5-bisoctyloxy)-1,4-phenylenevinylene]/single-walled carbon nanotube composite
Authors: Baibarac, M; Baltog, I; Srnaranda, I; Ilie, M; Scocioreanu, M; Mevellec, JY; Lefrant, S

Published: SEP 2014, SYNTHETIC METALS, 195, 285, DOI: 10.1016/j.synthmet.2014.06.010

Using surface-enhanced Raman scattering (SERS) and photoluminescence (PL) studies, new data concerning the electrochemical oxidation both of poly[(2,5-bisoctyloxy)-1,4-phenylene-vinylene] (BO-PPV) and the BO-PPV/HIPCO single-walled carbon nanotubes (SWNTs) composite are presented in this paper. The SERS studies performed at the excitation wavelengths of 752 nm and 532 nm of the BO-PPV/SWNTs composite that ensure the resonant excitation of the semiconductor and metallic nanotubes, respectively, reveal that the mixing of the two constituents results, on the one hand, in an isolation of semiconducting nanotubes from the bundles containing both metallic and semiconducting tubes and, on the other hand, in a functionalization of metallic SWNTs with BO-PPV. The isolation of semiconducting SWNTs is demonstrated by the narrowing of the G band and the change of the ratio between the intensities of the Raman lines situated in the low-frequency range that are assigned to the radial breathing vibrational modes. An additional isolation of the semiconducting nanotubes from the SWNTs bundles is reported when an electro-oxidation of the BO-PPV/SWNTs composite was performed in the potential range of (0; +2) V vs. Ag/AgCl. According to the Fourier transformed infra-red (FTIR) spectra and the SERS studies performed at an excitation wavelength of 1064 nm, the chemical interaction of BO-PPV with HIPCO SWNTs reveals a charge transfer between the two constituents that leads to the formation of BO-PPV covalently functionalized SWNTs. The BO-PPV luminescence quenching effect induced by the presence of SWNTs that consists of a change in the relative intensities of the three PL bands of the polymer peaked at 1.73 eV, 1.9 eV and 2.07 eV is due to the metallic tubes. The appearance of a new emission band at 2.32 eV was regularly observed when electrochemical oxidation of the BO-PPV/SWNTs composite was performed in the potential range of (0; +2) V. The PL band at 2.32 eV corresponds to ClO4- ions, which compensates the positive charges of BO-PPV generated during the electrochemical doping process. (C) 2014 Elsevier B.V. All rights reserved.
24. Spectroelectrochemical properties of the single walled carbon nanotubes functionalized with polydiphenylamine doped with heteropolyanions
Authors: Smaranda, I; Baibarac, M; Baltog, I; Mevellec, JY; Lefrant, S

Published: JAN 2013, JOURNAL OF SOLID STATE CHEMISTRY, 197, 360, DOI: 10.1016/j.jssc.2012.08.015

A combined chemical-electrochemical method was used for covalent functionalization of single-walled carbon nanotube (SWNT) with polydiphenylamine (PDPA) doped with heteropolyanions of H3PMo12O40 center dot xH(2)O. The functionalization process induces in Raman spectra of SWNTs the following changes: (i) an increase in relative intensity of the D band, accompanied a gradual up-shift of the G band in the case of the semiconducting tubes and a decrease in the relative intensity of band peaked at 1540 cm(-1) is remarked in the case of the metallic tubes; (ii) in the anti-Stokes Raman spectrum an increase in the relative intensity of Raman line of metallic tubes peaked at -1560 cm(-1) is remarked when the cycles number increases. The additional down-shift of the FTIR bands belonging to H3PMo12O40 heteropolyanions (at 881, 943 and 1055 cm(-1)) and PDPA (at 688, 736 and 1016 cm(-1)) originates in hindrance steric effects induced the covalent functionalization of SWNTs with polymer molecules. Using Raman scattering and FTIR spectroscopy we demonstrate that chemical polymerization of diphenylamine in the presence of H3PMo12O40 center dot xH(2)O and SWNTs results in a composite of the type blend based on PDPA in un-doped state and SWNTs doped with H3PMo12O40 heteropolyanions. (C) 2012 Elsevier Inc. All rights reserved.
25. NONLINEAR OPTICAL PROCESSES MANIFESTING AS ANDERSON LOCALIZATION OF LIGHT IN MESOSCOPIC MATERIALS
Authors: Baltog, I; Baibarac, M; Mihut, L; Smaranda, I; Lefrant, S

Published: APR-JUN 2012, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 13, 117, DOI:

Abnormal anti-Stokes Raman emission (AASRE) is defined by an anti-Stokes/Stokes intensity ratio much greater than expected on the basis of the equilibrium population of excited vibration states provided by the Boltzmann law. AASRE can be observed both in materials with intrinsic nonlinear optical properties as LiNbO3 or materials in which the nonlinear optical properties are induced by resonant optical excitation, as carbon nanotubes. Using a surface enhanced Raman scattering (SERS) device, consisting from single wall carbon nanotubes deposited on a rough Au or Ag support and LiNbO3 in form of powder, we demonstrate that under continuous single beam excitation they present AASRE whose properties are similar to a single beam pumped Coherent Anti-Stokes Raman Scattering. AASRE is usually accompanied by a coherent backscattering, it can be considered as Anderson localization of light that results from a wave-mixing mechanism of the incident laser light with a Stokes shifted Raman light produced by a spontaneous Raman light scattering process. The transport of the light inside of sample, giving rise to AASRE and coherent backscattering, is done by an elastic light scattering mechanism.
26. Hybrid organic-inorganic materials based on poly(o-phenylenediamine) and polyoxometallate functionalized carbon nanotubes
Authors: Baibarac, M; Baltog, I; Smaranda, I; Scocioreanu, M; Lefrant, S

Published: JAN 31 2011, JOURNAL OF MOLECULAR STRUCTURE, 985, 218, DOI: 10.1016/j.molstruc.2010.10.044

The chemical polymerization of o-phenylenediamine (OPD) on single-walled carbon nanotubes (SWCNTs) in the presence of phosphomolybdic acid (H3PMo12O40 xH(2)O) has been studied by surface enhanced resonant Raman scattering (SERRS) spectroscopy. One demonstrates that an organic-inorganic hybrid composite of the type poly(o-phenylenediamine)/polyoxometallate-functionalized SWCNTs is produced by the chemical interaction between polyoxometallate-functionalized SWCNTs and poly(o-phenylenediamine) (POPD) doped with [H2PMo12O40](-) ions. According to TEM investigations, a result of the chemical interaction of SWCNT with H3PMo12O40 xH(2)O is the formation into the composite mass of tube fragments of shorter length, which behave like closed shell fullerenes since Raman fingerprint is given by lines situated at 240-275 and 1450-1472 cm(-1). The chemical polymerization of OPD on SWCNTs achieved in the absence of H3PMo12O40 xH(2)O leads to a covalent functionalization of the wall side of the tubes, which is revealed in Raman spectra, recorded at the excitation wavelength of 514 nm, by an enhancement of the lines associated with the tangential vibrational modes of SWCNTs. Using FTIR spectroscopy, significant hindrance steric effects are evidenced in the POPD/polyoxometallate-functionalized SWCNT composite. (c) 2010 Elsevier B.V. All rights reserved.
27. Abnormal anti-Stokes Raman emission as a coherent anti-Stokes Raman scattering-like process in disordered media
Authors: Baltog, I; Baibarac, M; Smaranda, I; Lefrant, S

Published: MAY 14 2011, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 44, DOI: 10.1088/0953-4075/44/9/095401

In this paper, we demonstrate that, by continuous single beam excitation, one can generate an abnormal anti-Stokes Raman emission (AASRE) whose properties are similar to a coherent anti-Stokes Raman scattering (CARS). The effect has been observed in materials which possess intrinsically nonlinear properties (LiNbO(3) and CdS), which have the electric susceptibility of third order different from zero, chi((3)) not equal 0, as well as in materials that become nonlinear under resonant optical excitation. In the latter case, we used poly-3,4-ethylendioxythiophene (PEDOT) in its undoped state deposited electrochemically on Au support. Raman studies corroborated with images of optical microscopy demonstrate that the production of AASRE is conditioned by the existence of a particular morphology of the sample able to ensure efficient transport of the light inside the sample through a multiple light scattering mechanism. In this context, it was found that LiNbO3 and CdS in powder form as well as the PEDOT films layered on a rough Au substrate are suitable morphological forms. We explain AASRE as resulting from a wave-mixing mechanism of the incident laser light omega(l) with a Stokes-shifted Raman light omega(S) produced by a spontaneous Raman light scattering process, both strongly scattered inside the sample. As a CARS process, AASRE is conditioned by the achievement of phase-matching requirements, which makes the difference between the wave vectors of mixing light close to zero, Delta k = /2k(l) - k(S) - k(CARS) /approximate to 0. In condensed media, the small dispersion of the refractive index makes Delta k approximate to 0 so that the formation of a favourable phase-matching geometry may be accomplished even at a crossing angle. of travelling scattered light omega(l) and omega(S). For tightly focused beams, the requirement of phase matching relaxes; it is no longer sensitive to the Raman shift, so that a wide intense anti-Stokes Raman spectrum is observed at an angle larger than the Stokes Raman spectrum.
28. NON-LINEAR RAMAN SCATTERING EFFECTS GENERATED BY THE SURFACE PLASMONS EXCITATION
Authors: Baltog, I; Baibarac, M; Mihut, L; Smaranda, I

Published: 2010, ROMANIAN REPORTS IN PHYSICS, 62, 593, DOI:

An inciting and much debated subject in the surface enhanced Raman (SERS) studies is an unusual anti-Stokes Raman spectrum distinguished by an abnormal intensity, increasing with the vibrational wavenumber and some discrepancies with regard to the Stokes spectrum. We demonstrate that the abnormal anti-Stokes Raman emission on single walled carbon nanotubes and poly(3,4-ethylenedioxy thiophene) synthtetized electrochemically appears as a consequence of two corroborating effects: resonance, which occurs when the energy of the excitation light is near or coincident with the energy of an electronically allowed transition, and the SERS effect achieved by the excitation of surface plasmons. An abnormal intense Raman emission in the Stokes branch, reminiscent to a stimulated Raman effect, which increases exponentially with the intensity of exciting light is reported for the first time in the case of SWNTs.
29. Physico-chemical properties of two anhydrous azathioprine forms and their interaction with typical pharmaceutical excipients: highlighting new findings in drug formulation development
Authors: Barbatu, A; Lungan, MA; Toulbe, N; Smaranda, I; Daescu, M; Baibarac, M; Manta, CM

Published: , DRUG DEVELOPMENT AND INDUSTRIAL PHARMACY, DOI:

The physico-chemical properties of two anhydrous AZA forms and their interaction with typical pharmaceutical excipients were assessed by applying various methods (such as PXRD, HPLC, TG/DSC, IR, Raman, PL or UV-Vis) in order to highlight new directions for drug formulation. The stability assessment of AZA anhydrous forms I and II was performed in order to determine the risk of degradation of the active ingredient by accidental exposure to nonstandard conditions in the industrial environment, under different storage, transport or processing conditions. The benefits of form II include increased resistance to chemical degradation over a wide range of pH, but further control of storage and processing conditions is necessary to avoid polymorphic transformation into form I. The solubility assessment on the AZA solid forms in different environments that simulate the conditions of the gastrointestinal tract has the advantage of a significantly increased solubility of form II compared with the commercial form I due to the modification of the crystalline structure. In the case of capsules compared to AZA form I or II as powder, an improvement in their solubility was observed, promoted by the presence of one or more excipients in the formulation mixture.
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