Kinetics of photochemical reactions of multifunctional hybrid compounds based on spironaphthoxazines upon photoexcitation with light of different wavelengths

Four hybrid compounds (HCs), which molecules contain two or three photochromic fragments of different nature, have been examined by the nanosecond laser flash photolysis techniques using excitation wavelengths of 337 and 430 nm in methanol solutions. In HC molecules the photochromic spironaphthoxazine fragment, which is able to generate a colored merocyanine form B upon UV excitation, is linked to the substituted salicylideneaniline (SA) fragment, where reversible photochemical transformations from cis-enol to trans-keto form having distinguishably different absorption spectra can occur. An azobenzene group prones to trans–cis photoisomerization is the substituent in SA fragment in the fourth compound. Four intermediates of different nature were found. A decrease in the relative efficiency of the ESIPT process with respect to that of spiro-bond cleavage was found to be the result of the influence of the electronegative substituents in SA fragments. The excitation light wavelength was shown to be the main factor determining the relative yields of the intermediates of different nature for the hybrid compound with the azobenzene group. The mechanism of different intermediates formation is discussed.

► Spectral-kinetics characteristics of novel hybrid compounds (HC) were studied.
► The nature of substituents determines the number and properties of intermediates.
► The wavelength of excitation light determines the number of intermediates in HC 4.