The hydrogen bond effect on excited state mechanism for 2-isopropyl thioxanone in protic solvents: Experimental and theoretical investigation

Abstract In this work, the hydrogen bond effect on excited state mechanism of 2-isopropyl thioxanthone has been investigated in protic solvents by spectroscopic and computational chemistry methods. The two models of single hydrogen bond and double hydrogen bond provide the basis for the photophysical properties of ITX-solvent complexes, and the study of excited state hydrogen bond provides a theoretical basis for the emission of singlet and triplet states of ITX. We demonstrated that the intermolecular hydrogen bond C O⋯H O between ITX and protic solvents are significantly strengthened in the electronically excited-state upon photoexcitation of the ITX hydrogen-bonded complexes. Interestingly, hydrogen bonding inhibits molecular vibration and eliminates self-quenching and atmospheric oxygen quenching, which effectively inhibits non-radiative processes and improves the efficiency of emission. All the calculated spectral features are in good agreement with the spectral results recorded in experiments. This demonstrates that the ground state and excited state of the hydrogen-bonded ITX complexes presented here can well delineate in different solvents. This work provides a theoretical basis for the further development of the application of thioxanthone compounds.