Substituent Effect on the Photolability of 4-Aryl-1,4-Dihydropyridines.

The electronic nature of substituents attached to the 4-aryl moiety of 1,4-dihydropyridines strongly affects the photophysical and photochemical behavior of these family of compounds. The presence of an electron donor substituent on the 4-aryl moiety (or the absence of electron-withdrawing ones) modifies the luminescence lifetimes (τ < 100 ps) and diminishes the photodecomposition quantum yields. For electron-withdrawing substituents, the photodegradation quantum yield is affected by the media, changing more than two orders of magnitude as the polarity is increased. Studies in micellar media allow us to conclude that 4-aryl-1,4-dihydropyridines are located near to the interface; however, the surface charge of micelles has no effect on the photodegradation rate constant or the photoproducts profile. The main conclusion of this work is that the photolability of 4-aryl-1,4-dihydropyridines can be significantly reduced by the incorporation of antioxidant moieties.