Syetov Y. Vibrational spectra and luminescent properties of photoreactive systems in the solid state

The object is energy spectrum of photoreactive molecular crystals with proton transfer. The aim of the study is ascertainment of effects of intermolecular interaction and crystal structure disorder on the electronic and vibrational states of benzoxazoles undergoing excited state intramolecular photon transfer. Methods – fluorescence spectroscopy, Raman spectroscopy, infrared spectroscopy, theoretical modeling with the use of density functional theory, time-dependent density functional theory, density-functional based tight-binding and atom-atom potential methods. It is shown that intermolecular interaction causes lattice vibrations with frequencies in the range below 150 cm^{-1}, while the internal vibrations of crystals correspond to the molecular vibrations of enol structures with intramolecular hydrogen bonds between oxygen and nitrogen atoms. It is found that luminescence of crystalline compounds 2,5-di-(2-benzoxazolyl)phenol and 2,5-bis(2-benzoxazolyl)hydroquinone is caused by transitions between the states corresponding to both enol and keto structures of the molecules, in case of compound 2-(2′-hydroxyphenyl)benzoxazole – only by transitions between states corresponding to the keto. It is theoretically shown that restriction of internal rotation in the keto structures of the benzoxazole molecules inhibits the radiationless transitions from the first excited to ground state. Application field – design of organic components for optoelectronics.