Photophysics and photochemistry of the 2,4,6-triphenyl-2-benzyl-2H-thiopyran versus 2H-pyran derivatives

The photochemistry and photophysics of one thiopyran (2,4,6-triphenyl-2-benzyl-2H-thiopyran) and two pyran (2,4,6-triphenyl-2H-pyran and 2,4-dimethyl-2,6-diphenyl-2H-pyran) derivatives were investigated by stationary and time resolved techniques. Both theory and experiments indicated a π,π* character for the lowest singlet states of these molecules, located in the UV region approximately at the same energy. Upon stationary UV irradiation at low temperature, colourless photoproducts were formed from the pyran derivatives, while coloured compound(s) were obtained from the thiopyran. Long-lived transients were observed at room temperature, which were assigned to the photoproducts obtained at low temperature; only in one case (2,4,6-triphenyl-2H-pyran) a triplet precursor was detected.