Control of chromophore symmetry by positional isomerism of peripheral substituents.

The first example of the control of porphyrinoid chromophore symmetry based on the positional isomerism of peripheral substituents has been achieved by preparing tetraazaporphyrins (TAPs) with C(4h), D(2h), C(2v), and C(s) symmetry due to the relative arrangement of peripheral tert-butylamino and cyano groups as push and pull substituents, respectively. The four structural isomers were successfully isolated and characterized by (1)H NMR spectroscopy and X-ray crystallography. The band morphology in the Q-band region varies depending on the molecular symmetry due to the significant perturbation introduced into the chromophore by the push and pull substituents.