Transient Absorption Spectroscopy of A Twisted intramolecular Charge Transfer (TICT) State in a DCM Molecule Analyzed by Isosbestic Points

Abstract

An organic dye molecule, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), was investigated by UV-pump/visible-probe transient absorption spectroscopy with populating the S-2 state in a twisted conformation of an electron donor, which is responsible for a twisted intramolecular charge transfer (TICT) excited state. We observed the formation and completion of a TICT state from the spectral change of a temporary isosbestic point. The solvation relaxation (similar to 3 ps) of the TICT state was estimated, which is shorter than that of the intramolecular charge transfer (ICT) state (similar to 10 ps). The isosbestic points were shifted in the excited-state dynamics of the TICT state toward a red wavelength region and in that of the ICT state toward the blue region with a different temporal range of times. This study presented the photoinduced dynamics of an emissive intermediate TICT state showing the spectral change of isosbestic points in ultrafast time-resolved transient absorption spectroscopy.