H.M. Suresh Kumar

Solvents effect on the absorption and fluorescence spectra of 7-diethylamino-3-thenoylcoumarin: Evaluation and correlation between solvatochromism and solvent polarity parameters

Effect of solvents of varying polarities on absorption and fluorescence spectra and dipole moment of laser dye: 7-diethylamino-3-thenoylcoumarin (DETC) has been investigated. A small band shift is obtained in the absorption spectra compared to emission spectra. The spectral shifts were correlated with Catalans parameters using linear solvation energy relationship. It reveals that non-specific interaction measured by solvent polarity has more influence on absorption and solvent dipolarity contribution is significant in case of fluorescence. A bathochromic shift observed in absorption and emission spectra with increasing solvent polarity, which implied that the transition involved is π→π(∗). The solvatochromic correlations were used to estimate the excited state dipole moment using experimentally determined ground state dipole moment. The observed single-state excited state dipole moment is found to be greater than the ground state.

Effect of solvents on the spectroscopic properties of LD-489 & LD-473: estimation of ground and excited state dipole moments by solvatochromic shift method.

The absorption and fluorescence spectra of 6,7,8,9-tetrahydro-6,8,9-trimethyl-4-(trifluoro methyl)-2H-pyrano[2,3-b][1,8]naphthyridin-2-one (LD-489) and 1,2,3,8-tetrahydro-1,2,3,3,8-pentamethyl-5-(trifluoromethyl)-7H-pyrrolo[3,2-g]quinolin-7-one (LD-473) have been recorded at room temperature in different solvents and 1,4-dioxane-acetonitrile solvent mixtures. The UV-Visible absorption spectra are less sensitive to solvent polarity than the corresponding fluorescence spectra in both the dyes which show pronounced solvatochromic effect. The effects of solvents upon the spectral properties are analyzed using Lippert-Mataga polarity function, Richardts microscopic solvent polarity parameter and Cataláns multiple linear regression approach. Both general solute-solvent interactions and specific interactions are operative in these systems. The solvatochromic correlations are used to estimate excited state dipole moments using experimentally determined ground state dipole moments. The excited state dipole moment for both the dyes are found to be larger than their corresponding ground state dipole moment and is interpreted based on their resonance structures.

Effect of Solvent Polarity on Fluorescence Quenching of New Indole Derivatives by CCl4

ABSTRACT The fluorescence quenching of solutes 3-[5′-methyl-3′-phenylindol-2′-yl]-s-triazolo [3,4-b] [1,3,4] thiadiazol-6(5H)-thione (MPITTT) and 3-phenyl-2,5-bis-[thiosemicarbazido] indole (PbisTI) by carbon tetrachloride (CCl4) in dioxane and acetonitrile mixtures has been studied at room temperature by steady-state fluorescence measurements. The positive deviation from linearity has been observed in the Stern–Volmer (S-V) plots for both fluorophores in different composition of mixed solvents even at moderate CCl4 concentration (0.10 mol dm−3). Various quenching parameters of the quenching processes have been determined using the extended S-V equation and have been found to be dependent on the solvent polarity. Further, with the use of the finite sink approximation model, it is concluded that the bimolecular quenching reactions are diffusion limited, and the distance parameter R′ and mutual diffusion coefficient D are estimated independently.

Estimation of ground and excited state dipole moment of laser dyes C504T and C521T using solvatochromic shifts of absorption and fluorescence spectra

The absorption and fluorescence spectra of laser dyes: coumarin 504T (C504T) and coumarin 521T (C521T) have been recorded at room temperature in a series of non-polar and polar solvents. The spectra of these dyes showed bathochromic shift with increasing in solvent polarity indicating the involvement of π→π⁎ transition. Kamlet-Taft and Catalan solvent parameters were used to analyze the effect of solvents on C504T and C521T molecules. The study reveals that both general solute-solvent interactions and specific interactions are operative in these two systems. The ground state dipole moment was estimated using Guggenheims method and also by quantum mechanical calculations. The solvatochromic data were used to determine the excited state dipole moment (μ(e)). It is observed that dipole moment value of excited state (μ(e)) is higher than that of the ground state in both the laser dyes indicating that these dyes are more polar in nature in the excited state than in the ground state.

Effect of quencher and temperature on fluorescence intensity of laser dyes: DETC and C504T

Fluorescence quenching of 7- Diethylamino-3-thenoylcoumarin (DETC) and 2,3,6,7-tetrahydro-1,1,7,7-tetramethyl11-oxo-1H,5H,11H- [1]benzopyrano[6,7,8-ij]quinolizine-10-carboxylic acid, ethyl ester (C504T) by aniline(AN), dimethylaniline (DMA) and diethylaniline (DEA) was investigated in toluene by steady state and transient methods. The quenching parameters like frequency of encounter (kd), probability of quenching per encounter (p), quenching rate parameters (kq) and activation energy of quenching (Ea) were determined experimentally. The kq values determined by steady state and time-resolved methods for the both dyes were found to be same, indicating the dynamic nature of interaction. Magnitudes of p and Ea suggested that the quenching reaction is predominantly controlled by material diffusion. The quenching mechanism is rationalized in terms of electron transfer (ET) from donors (aromatic amines) to the acceptors (coumarin derivatives) confirmed by correlating kq with free energy changes (ΔG°). Further, an effect of temperature on fluorescence intensity was carried out in toluene and methanol solvents. Fluorescence intensity of both the dyes decreases with increase in temperature. Temperature quenching in case of C504T is due to intersystem crossing S1→T2, whereas for DETC, quenching is due to intersystem crossing S1→T2 and ICT→TICT transition.

Co-60 γ-irradiation effect on linear, nonlinear optical and electrical properties of a semiorganic L-alanine barium nitrate (LABN) crystal

ABSTRACT Single crystals of L-alanine barium nitrate (LABN) were grown by slow evaporation method from aqueous solution under optimized conditions. These crystals were studied by various characterizations tools viz., structural, FTIR analysis, UV absorption, nonlinear optical (NLO), thermal and dielectric studies. The structural study revealed that LABN fit into cubic crystal system with space group . The TGA-DTA study infers that the crystal is stable up to 210 °C. The recorded UV-vis-NIR spectrum shows that, the crystal has wide window and high transmittance. The dielectric parameters as a function of frequency and SHG efficiency by Kurtz powder method of LABN crystal were studied. Further, the crystals were exposed to 1, 3 and 5 Mrad dosage Co-60 gamma radiations and studied the modifications in UV absorption, electrical and nonlinear optical properties. It is observed that the color of the crystal is changed from transparent to yellow and energy gap is decreased upon irradiation. The dc conductivity is increased with increasing in the dosage of gamma radiation, where as SHG efficiency increased for 1 Mrad and then decreased marginally with increasing in the dosage.

Growth and characterization of NLO crystal: L-leucine phthalic acid potassium iodide

Abstract A new semi-organic non linear optical crystal, L-leucine phthalic acid potassium iodide (LLPPI) has been grown from an aqueous solution by slow evaporation method. The grown crystals were subjected to different characterizations, such as single crystal XRD, FT-IR, UV-Vis, TGA, SEM, EDAX, micro hardness, dielectric and powder SHG. Single crystal structure was determined from X-ray diffraction data and it revealed that the crystal belongs to triclinic system with the space group P1. The vibrational frequencies of various functional groups were derived from FT-IR spectrum. Thermal stability of the grown crystal was investigated by TG-DTA studies and it was observed that the crystal was thermally stable up to 192 °C. Optical absorption study was carried out and a good transparency in the entire visible region was observed at the lower cutoff wavelength of 227 nm. Dielectric study was performed as a function of frequency and normal dielectric behavior was observed. The micro hardness test was carried out and the load dependent hardness was measured. Kurtz powder method was employed to explore the NLO characteristics of the grown crystal.

Growth and charatcterisation of mercuric chloride doped urea single crystals

Abstract Semiorganic non-linear optical single crystals of urea mercuric chloride were grown from aqueous solution using slow evaporation method. The grown crystals were subjected to different characterisations Viz., XRD, FTIR, UV, TGA and powder SHG. XRD study reveals that the crystal belongs to triclinic system with the space group P1. The vibrational frequencies of various functional groups have been derived from FTIR spectrum. Thermal stability of the grown crystal was investigated by TG-DTA studies and it is observed that the title compound is thermally stable up to 170 °C. Optical absorption study has been carried out and a good transparency in the entire visible region is observed with the lower cut-off wavelength of 245 nm. Kurtz powder method was employed to explore the non-linear optical characteristics of the grown crystal.

N1-(4-Methyl­phen­yl)piperidine-1,4-dicarboxamide

In the title compound, C14H19N3O2, the heterocycle adopts a 1 C 4 conformation with the N atom being one of the flap atoms. In the crystal, classical N—H⋯O hydrogen bonds and C—H⋯O contacts connect the molecules into a three-dimensional network.