NIR-emitting boradiazaindacene fluorophores -TD-DFT studies on electronic structure and photophysical properties.

Density Functional Theory [B3LYP/6-31G(d)] and Time Dependent Density Functional Theory [TD-B3LYP/6-31G(d)] computations have been used to have more understanding of the structural, molecular, electronic and photophysical parameters of recently synthesized near IR-emitting acid switchable di-styryl BODIPY dyes. The structures have been optimized using function B3LYP and basis set used was 6-31G(d) for all the atoms and their geometries which are correlated with corresponding rotational isomers including rotational isomers of diprotonated forms in chloroform solvent. The observed energies of the optimized molecules suggest that there may be rotation about C-C single bond as the observed energy barrier is very low. The results of TD-DFT suggest that there is very good match between the observed and calculated absorptions diprotonated forms of one molecule. There is also good match between experimental and theoretical emission of neutral forms. More deviations are observed in the case emission of the diprotonated forms.