NLOphoric benzyl substituted BODIPY and BOPHY: A comprehensive linear and nonlinear optical study by spectroscopic, DFT and Z-scan measurement.

BOPHY (BPY) and BODIPY (BDY) dye bearing benzyl group (Bn) at 4,4' and 2,6 position respectively were synthesized and characterized. The fluorescence decay measurements were performed which reveal that benzyl BOPHY (Bn-BPY) has shorter fluorescence lifetime compared to benzyl BODIPY (Bn-BDY). The difference in transition dipole moment is found to be 6.93 and 11.3 D for Bn-BDY and Bn-BPY respectively in toluene. The molecular electrostatic potential (MEP) plot shows Bn-BDY is more polarised compared to Bn-BPY. The nonlinear optical (NLO) property was evaluated using Z-scan measurement. The molecular electronic arrangement of Bn-BPY significantly affects the nonlinear absorption properties resulting into reverse saturable absorption (nonlinear absorption coefficient β = 0.256 × 10 m/W). In contrast, the Bn-BDY displays saturable absorption character. The calculated third-order nonlinear susceptibility χ value is 12.23 × 10 esu and 2.49 × 10 esu for Bn-BDY and Bn-BPY respectively. The power limiting behaviour of Bn-BPY displays limiting threshold energy around 70 Jcm with clamped output at ~35 Jcm.