Triplet-sensitized photobehaviour of the three stereoisomers of 1,4-distyrylbenzene and some aza-analogues

The triplet spectral properties of the three stereoisomers (EE, ZE and ZZ) of 1,4-distyrylbenzene and some symmetric EE-aza-analogues, bearing a nitrogen heteroatom in the side (2′-pyridyl, 4′-pyridyl or 2′-quinolyl) or in the central (2,5-pyridine) arene rings, have been investigated by laser flash photolysis in different solvents and compared with those of the parent hydrocarbon. The quantum yields of the triplet-sensitized photoisomerization have also been measured. Adiabatic formation of the excited 3EE* isomer by irradiation of the other geometrical isomers has been detected by transient spectroscopy. The effect of the substrate concentration on the sensitized photoisomerization quantum yield revealed the occurrence of a quantum chain process, as known for similar arylolefins.