Photophysics and photochemistry of the EE and ZE isomers of 1-(n-pyridyl)-4-phenyl-1,3-butadiene (n=2, 3 and 4)

The positional isomers of 1-(n-pyridyl)-4-phenyl-1,3-butadiene (n = 2, 3 an d 4) have been synthesized in the EE and ZE geometries by common routes and characterized by spectrometric techniques. Their excited state properties were investigated by stationary and pulsed fluorimetric techniques and by l aser flash photolysis. This paper reports the spectral, photophysical and p hotochemical behaviour of the EE and ZE isomers in a non-polar solvent. The photoisomerization proceeds through singlet, diabatic and/or adiabatic mec hanisms with generally low quantum yield, owing to the role of internal con version (markedly more important for n = 2). The role of intramolecular hyd rogen bonds on the excited state properties of the ZE isomer of the 2-pyrid yl derivative is particularly described.