The electronic structures and photophysical properties of rigid coumarin dyes have been studied by using quantum chemical methods. The ground-state geometries of these dyes were optimized using the Density Functional Theory (DFT) methods. The lowest singlet excited state was optimized using Time -Dependent Density Functional Theory [TD-B3LYP/6-31G(d)]. On the basis of ground- and excited-state geometries, the absorption and emission spectra have been calculated using the DFT and TD-DFT method. All the calculations were carried out in gas phase and in acetonitrile medium. The results show that the absorption maxima and fluorescence emission maxima calculated using the Time-Dependent Density Functional Theory is in good agreement with the available experimental results. To understand the Non- Linear Optical properties of coumarin dyes we computed dipole moment (μ), electronic polarizability (α), mean first hyperpolarizability (βo) and second hyperpolarizability (γ) using B3LYP density functional theory method in conjunction with 6-31G(d) basis set.

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Three new fluorescent phenalenone derivatives incorporating bexozazolyl, benzothiazolyl and benzimidazolyl rings have been synthesized from the intermediate 3-(1,3-benzazol-2-yl) naphthalen-2-ol by reacting with glycerol. The synthesized phenalenone derivatives were well characterized by using FT-IR, (1)HNMR, (13)CNMR and Mass spectroscopy. The photophysical properties of these phenalenone derivatives show that these dyes absorb in the range of 300-429 nm and emitted in the range of 348-578 nm. The relative fluorescence quantum yields of these derivatives were determined by using fluorescein, tinopal and anthracene as the reference standards. Photophysical properties of the synthesized phenalenone dyes were evaluated by UV-Visible spectroscopy and compared with the computed vertical excitations obtained from TD-DFT. Thermal stability of the compounds were studied by using thermo gravimetric analysis and results show that compounds are thermally stable up to 298-347 °C.

A new class of red emitting extensively conjugated donor-π-acceptor type dyes bearing coumarin units are investigated for nonlinear optical properties. The photophysical behaviour and the relation between structure and properties of the coumarin "push-pull" derivatives were investigated based on solvatochromism and experimentally observed shifts in emission maxima. The electronic coupling for the electron transfer reaction for the coumarin dyes are calculated with the generalized Mulliken-Hush method. We evaluated non-linear optical (NLO) properties of coumarin dyes using both experimental solvent dependent shift method and computational method. All the investigated coumarin dyes are showing large value for first (β) and second hyperpolarizability (γ). Density functional theory [B3LYP/6-31G(d)] and time dependent density functional theory (TDDFT) computations have been employed to have more understanding of structural, molecular, electronic and photophysical parameters of the coumarin dyes.

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New derivatives of (benzo[d]azolyl)-benzo[f]chromenone were synthesized from the intermediate 3-(1,3-benzazol-2-yl)naphthalen-2-ol, obtained from 3-hydroxynaphthalene-2-carboxylic acid and 2-amino phenol in the presence of PCl3 in chlorobenzene at 130-135 °C. The compounds were characterized by FT-IR, (1) H NMR, mass spectroscopy and elemental analysis. The synthesized compounds are fluorescent which absorb in the range of 296 to 332 nm while emit in the range of 368 to 404 nm. The experimental absorption and emission wavelengths for the compounds 5 and 6 are in good agreement with those predicted using the Time-Dependent Density Functional Theory (TD-DFT) [B3LYP/6-31G(d)]. The largest wavelength difference between the experimental and computed absorption maxima was 29 nm (tetrahedrofuran) for compound 5 while for emission it was 61 nm (dichloromethane) for compound 7. The emission intensities of all the compounds decrease continuously as the viscosity of the microenvironment increases. The compounds are thermally stable up to a temperature range of 300 to 350 °C.