Conformational equilibrium in trans-aza-aryl-ethylenes: n-styrylquinolines and n-styrylisoquinolines

The ground state conformational equilibrium of trans-n-styrylquinolines (n=2, 3, 4, 6, 7 and 8) and n-styrylisoquinolines (n = 1 and 3) has been studied in polar and apolar solvents. The fluorescence and trans→cis photoisomerization properties show that the presence of the hetero- cyclic nitrogen does not modify the steric requirements for the stability of the possible conformers. The influence of the styryl position with respect to the heteroatom, and of the solvent on the equilibrium composition and on the photophysical behaviour of the individual rotamers has been particularly investigated.