Hydrogen-bonded complexes of lumichrome.

Hydrogen bonds were shown to play an important role in the lumichrome photophysics and photochemistry both in solutions and in the solid state. In solutions, lumichrome can form hydrogen-bonded complexes with a variety of molecules, such as acetic acid or methanol, as supported by spectral and equilibrium studies. Photoexcitation of some hydrogen-bonded complexes, having appropriate configuration, as in the case of acetic acid, may lead to excited-state proton transfer, resulting in formation of the isoalloxazinic structure, detectable by its characteristic emission, distinct from that of the intrinsically alloxazinic lumichrome.

Photoprotection of 1,4-dihydropyridine derivatives by dyes.

The possibility of increasing the photochemical stability of nisoldipine by using indigotine and azorubine as photoprotectors has been studied. The course of the photodegradation was monitored by means of UV-vis spectrophotometry and HPLC. Quantitative assessments of the nisoldipine photodegradation included evaluation of the quantum yields and kinetic parameters.