Effect of donor and π-spacer for non-linear optical property: Synthesis, photophysical studies, and Z-scan analysis

Abstract

The impact of donor and π-spacer on linear and non-linear optical (NLO) properties was investigated by designing and synthesizing dyes having diethylamino coumarin and julolidine-based coumarin donors containing thiophene and phenyl-spacer with ethyl cyanoacrylate acceptor. Density functional theory (DFT), time-dependent DFT, and Z-scan methods were opted for this study. Diethylamino coumarin and julolidine-based coumarin dyes showed maximum absorption and emission in the range of 462–524 and 480–544, and 515–641 and 520–663 nm, respectively. A julolidine-based coumarin and thiophene spacer containing dye and diethylamino-based coumarin with phenyl spacer showed the most red-shifted and blue-shifted absorption and emission properties, respectively. All dyes showed considerable viscosity sensitivity in polar (PEG: ethanol) and non-polar (Paraffin: toluene) media. Also, the title dyes showed good thermal stability above 300 °C. Further, the theoretical investigation suggested dyes with julolidine-based coumarin and thiophene-spacer have better CT (through FMO, MEP, BLA, BOA, and QC calculations) λVert and hence showed superior linear and NLO properties in solvent phases. Lastly, the results obtained from the Z-scan method also showed similar results as revealed by the theoretical study.