Cis-trans isomerisation and absorption properties of the ring-extended azobenzene

A series of azobenzene derivatives which differ in the number of rings attached to benzene is investigated using dispersion-corrected density-functional theoretical methods. The studies on the effect of extended rings on the energy of cis and trans isomers (Delta Ecis-trans) of the derivatives revealed that Delta Ecis-trans is increased from azobenzene to azoanthracene, however, decreased when the rings are extended in two dimensions. The time-dependent density-functional theoretical studies showed that the extension of rings in two-dimension shifts absorption maximum from ultraviolet to visible region. The investigations on fluorine and amino-substituted derivatives of azocoronene showed its cis isomer as lower in energy than trans isomer.