Coumarin Push-Pull NLOphores with Red Emission: Solvatochromic and Theoretical Approach.

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.