Comparing the linear and non-linear optical properties of keto-enol forms of N-alkyl, N-aryl, and O-alkyl substituted 2-Hydroxybenzophenone

The Geometrical, electronical, spectral, linear, and non-linear optical properties (NLO) of keto-enol forms of 2-hydroxybenzophenone (2-HBp) derivatives were examined. Ten pairs of 2-HBp derivatives having D-π-A framework with N-alkyl (ethyl, julolidine), N-aryl (phenyl), O-methyl, groups as donor, phenyl ring as a spacer, and carbonyl group linked to phenyl ring consisting of either mono or dicarboxylic acid group as acceptor, were selected. DFT results suggest that the keto form is stable in the S₀ and S₁ states. Further, IR spectra, CV analysis, experimental absorption maxima, and TD-DFT results support the existence of 2-HBp derivatives in keto form. Thermogravimetric analysis shows that 2-HBp derivatives have remarkable thermal stability (∼200 °C), enabling their practical application in NLO. Further, DFT and TD-DFT results show that the keto form of 2-HBp derivatives with lower BLA, higher μ, ω, η, Γ, and hyperpolarizability exhibits superior NLO properties compared to the enol form of 2-HBp derivatives.