Coumarin-Rhodamine Hybrids - Synthesis, Photophysical Properties, NLO Properties and DFT Studies

Solvatochromic and solvatofluoric behaviour of three coumarin rhodamine hybrid dyes (Cou-Rhod1, Cou-Rhod2 and Cou-Rhod3) have been studied in ten different solvents with varying polarity. The pH (1-10) study was done to investigate the spirocyclic ring opening. All the dyes show charge transfer phenomenon in local as well as charge transfer excitation. The non-linear optical properties of coumarin rhodamine hybrid dyes were studied using solvatochromic method (highest value of alpha(CT) for Cou-Rhod1= 2.44 X 10(-23); highest value of beta(CT) for Cou-Rhod2 = 0.14 X 10(-28) and the highest value of gamma for Cou-Rhod2 = 0.02 X 10(-34)) and computational (highest value of alpha(0) for Cou-Rhod 3= 9.89 X 10(-23); highest value of alpha(0) for Cou-Rhod1 = 0.90 X 10(-28) and highest value of gamma for Cou-Rhod3 = 5.10 X 10(-34)) approach. As the non-radiative rate constant increases quantum yield of the dyes decreases. Correlation of calculated radiative lifetime (tau), radiative (K-r) and non-radiative rate constant (K-nr) has been made to explain the quantum yield of dyes using Strickler-Berg equation. The charge transfer behaviour, structural parameters and non-linear optical properties of the dyes are well described by DFT and TD-DFT calculations.