Ultrafast excited state dynamics, direct and back [2 + 2]-cross-photocycloaddition of a styryl dye–stilbene charge transfer complex

Abstract This research is dedicated to the study of bis(ammoniopropyl) derivative of (E)-4-(4-mercaptostyryl)pyridine dye (2), forming a highly stable bimolecular complex with a bis(18-crown-6 ether) derivative of (E)-stilbene (1) in solution owing to ditopic coordination via hydrogen bonds. The spectral-kinetic parameters of E isomer of the dye and its complex were obtained using steady-state absorption, fluorescence, and time-resolved absorption spectroscopy. The stability constant of the complex, quantum yields of cross-PCA and retro-PCA reactions were determined by spectrophotometric titration methods. According to density functional theory calculations, E–Z photoisomerization of dye 2 occurs via non-radiative deactivation from intermediate twisted (TICT) state. The detailed study of stereospecific [2 + 2]-cross-photocycloaddition (cross-PCA) of complex (E)-1·(E)-2 and back reaction of cross-PCA product (rctt-3) was carried out. The complexation reaction of cyclobutane rctt-3 with Ba2+ ions has been investigated. A highly efficient direct intrasupramolecular photoelectron transfer and the back electron transfer of a moderate efficiency were found for the complex (E)-1·(E)-2.