Non-linear optical behavior of benzothiazole based chromophores: Second harmonic generation

The linear as well as second-order non-linear optical behavior of benzothiazole based chromophores and their corresponding boron (III) chelated derivatives has been discerned. The participating high energy (HE) and low energy (LE) electronic transitions of these compounds and the corresponding orbitals have been characterized on the basis of time dependent density functional theory (TD-DFT) calculations. The experimental electronic spectral data as well as electrochemical data correlated well with the calculated band gaps and the natural bond orbital (NBO) values, respectively. The experimentally determined second-order polarizability, beta, values show structure dependence and good correlation with the electronic absorption data. The boron (III) chelated chromophores exhibit higher values of beta(HRS) compared to their non-chelated counterparts as expected from the pi-electron density delocalization in the chromophores, although the trend in beta values corrected for resonance enhancement changed. Significant thermal stability of these chromophores (up to 300 degrees C) is an additional attribute that purports these chromophores as promising candidates for electro-optics and related applications.