Red Emitting Coumarin-Azo Dyes : Synthesis, Characterization, Linear and Non-linear Optical Properties-Experimental...

The coumarin molecules with 7-(N,N-diethylamino) substitution and aryl azo (Ar-N=N-) at 3-position were synthesized, by reacting diazonium salt of substituted amines and 7-(N, N-diethylamino)-4-hydroxy coumarin under basic conditions. They were found to be fluorescent despite the presence of azo group. The azo group rotation was blocked by complexing with -BF2, so as to get a red shift in absorption. The azo molecules show charge transfer, whereas BF2-complexes do not. The dipole moment ratios between the ground and excited states calculated suggest highly polar excited state and an intra-molecular charge transfer at the excited state in the case of azo dyes. The NLO properties were calculated by solvatochromic method and computationally. Second order hyperpolarizability was found to be 46 to 1083 times more than urea. DFT and TDTDF calculations were performed to understand the electronic properties of the molecules at the ground as well as excited states.