Photophysical Approach of Biological Active Benzofuran Derivatized Pyrrole with Green Synthesized Silver NPs Using C. Roseus Leaves: Computational and Spectroscopic Study

The electronic absorption and fluorescence emission spectra of N-(2,5-dimethyl-pyrrol-1-yl)-2-(5-methoxybenzofuran-3-yl)acetamide (DPMA) molecule were recorded in various solvents at room temperature with the aim of estimation of ground state (\({\mu }_{g}\)) and excited states (\({\mu }_{e}\)) dipole moments using Lippert’s, Bakshiev’s and Kawski-Chamma-Viallete’s equations. The results were signified that, the excited state dipole moment is greater than the ground state dipole moment, which indicates the excited state dipole moment is more polar than the ground state dipole moment. Ecofriendly green synthesis of silver nanoparticles (Ag NPs) were synthesized using catharanthus roseus (C.R) leaf extract was done. These synthesized Ag NPs were used as fluorescence quenchers. Fluorescence lifetime measurement is carried out using time correlated single photon counting technique of DPMA molecule with various concentrations of Ag NPs. A linear Stern-Volmer (S-V) plot was obtained in steady state and transient state method. Furthermore we have estimated computational calculations such as ground state optimized geometry, molecular electrostatic potential (MEP), highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), experimental and theoretical energy band gap, solvent polarity and normalized solvent polarity values. Morphology and sizes of green synthesized silver NPs were characterized by transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDX) and also characterized by UV-Visible absorption.

Study of Solvent Effect in 2, 5-DPAPMC Dye Using Different Solvent Polarity Parameters and Estimation of Dipole Moments

The solvent effect on absorption and fluorescence spectra of a ketocyanine dye 2,5-di[(E)-1-(4- dipropylaminophenyl) methylidine]-1-cyclopentanone (2,5-DPAPMC) is analysed using Lippert-Mataga bulk polarity function, Reichardt’s microscopic solvent polarity parameter and Kamlet’s multipl e linear regression approach. The spectral properties better follows Reichardt’s microscopic solvent polarity parameter than Lippert-Mataga bulk polarity parameter. This indicates the presence of both general solute – solvent interactions and specific interactions. Kamlet’s multiple linear regression approach indicates the major role of polarizability/dipolarity solvent influence than HBD and HBA. The spectral data in different solvents is used to estimate excited state dipole moment using theoretically determined ground state dipole moment. The excited state dipole moment of dye is found to be larger than its corresponding ground state dipole moment and, ground and excited state dipole moments are not parallel, but subtends an angle of 29 o .

RELATIONSHIPS BETWEEN DIFFERENT-ORDER POLARIZABILITIES AND GROUND STATE DIPOLE MOMENT

A number of charge transferring molecules with varying electron donor, acceptor and π-conjugative paths have been considered for the theoretical study of their NLO properties in terms of the linear polarizability and the ground state dipole moment. The equilibrium structures are calculated at the HF, MP2 and B3LYP levels, respectively. The longitudinal components of NLO coefficients are calculated by using HF, MP2, B3LYP, BHHLYP, CAM-B3LYP, and wB97XD methods for 6-31+G(p,d) and 6-311++G(p,d) basis sets. The hyperpolarizabilities obtained at different levels of calculation showed a fairly consistent trend. The relationships between hyperpolarizabilities, polarizability and ground state dipole moment have been proposed by considering only the two-level term in the standard sum-over-state (SOS) expressions and the generalized Thomas–Kuhn (TK) sum rule. The ab initio calculated first- and second-hyperpolarizabilities fairly correlate with the reduced 2-level contributions relating to the linear polarizability and ground state dipole moment. For a given length of conjugation the stronger enhancement of cubic polarizability arises from the increase of quadratic polarizability for comparable values of linear polarizability and dipole moment. The idea developed in the present work can be used to make a rational design of potential NLO-phores.

Evidences of Conformational Fluctuations of 2-methylaminofluorenone and 2-dimethylaminofluorenone in Polar Solvents

The absorption and fluorescence spectra of 2-methylaminofluorenone (2MAFl) and 2-dimethylaminofluorenone (2DMAFl) were determined at 293 K in a variety of solvents with different polarities. The spectral data were used, in combination with the 2MAFl and 2DMAFl ground state dipole moment (μg), to evaluate μe of the S1 state, to determine the outer-sphere solvent reorganization energy λouter, and the intramolecular reorganization energies: λ1 (associated with vibrations for which hv < kT) and λi(hv > kT). At 77 K the fluorescence spectra in a non-polar solvent are shifted to longer wavelengths. In polar solvents, for both molecules the behavior is opposite. The fluorescence decay data for 2MAFl and 2DMAFl in non-polar solvents are very well fitted by oneexponential functions, while in polar solvents by two-exponential functions. The spectroscopic data distinctly show that both studied molecules in polar solvents form an inhomogeneous emitting system.

ENHANCEMENT OF EFFECTIVE SECOND-ORDER NONLINEARITY IN POLED POLYMERS BY INTRODUCING THE CHROMOPHORES WITH LOW GROUND STATE DIPOLE MOMENT

The strategy of introducing the chromophores with low ground state dipole moment had been discussed to overcome the effect of the electrostatic interaction between the chromophores in the poled polymer films on its nonlinearity. As a result, the effective nonlinear optical coefficient d33 of the poled films, containing the chromophores with μg in the range of 3.5–5.5 D, will enhance at least 15%, even over 30%, compared to that of 7.5 D if the first hyperpolarizabilities (β) of chromophores are in the same magnitudes. And, under the above assumption, the same level of the d33 could even be achieved by utilizing the chromophores with μg as low as 2.2 D.