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This paper presents a simple, low cost method of synthesizing TiO2 nanoparticles by sol-gel method, where titanium isopropoxide is used as a starting material. Further, same TiO2 is used to sensitize 2-cyano-3-(4-(7-(5-(4-(diphenylamino) phenyl)-4-octylthiophen-2-yl) benzo[c] [1, 2, 5] thiadiazol-4yl)phenyl) acrylic acid (RK-1 dye) and Di-tetrabutylammonium cis-bis (isothiocyanato) bis (2,2'-bipyridyl-4,4'-dicarboxylato) ruthenium(II) (N-719 dye) for light harvesting applications. Anatase structure and average particle size of 7.3 nm were confirmed from XRD pattern. From SEM, it was noticed that particles were of varying size and shape and aggregation with clear porosity. FTIR spectra reveal Ti-O bond corresponding to 483 cm-1 and from UV-Vis absorption, energy band gap was found to be 3.2 eV. Photocurrent density (J)-photovoltage (V) characteristic of DSSC of different thicknesses of TiO2 were obtained, it was observed that optimum solar energy to electricity conversion efficiency () for RK-1 dye and N-719 dye 4.08 % and 5.12 % with TiO2 thickness of 5.4 μm and 8.6 μm respectively under AM 1.5 irradiation (1000 W/m 2) conditions.

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The absorption and emission spectra of two coumarins namely 7, 8 benzo-4-azidomethyl coumarin (C(1)) and 6-methoxy-4-azidomethyl coumarin (C(2)) have been recorded at room temperature in solvents of different polarities. The ground state dipole moments (μ(g)) of two coumarins were determined experimentally by Guggenheim method. The exited state (μ(e)) dipole moments were estimated from Lippert's, Bakhshievs and Chamma-Viallet's equations by using the variation of Stoke's shift with the solvent dielectric constant and refractive index. The ground and excited state dipole moments were calculated by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground state dipole moments. It was observed that dipole moments of excited state were higher than those of the ground state, indicating a substantial redistribution of the π-electron densities in a more polar excited state for two coumarins.

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