SERS and DFT study of silver nano particle induced dark isomerisation in 1H-2(Phenylazo) imidazole

Raman spectra and SERS of 1H-2(Phenylazo) imidazole (PaiH) adsorbed on silver nano particles are reported. Monomolecular layer is formed at a concentration of 5 × 10−6 M. A trans-to-cis isomerisation of PaiH is suggested by the cis-signature peak at 570 cm−1. In absorption spectra a single π–π∗ band at 358 nm is observed at higher concentrations whereas the π–π∗ and the n–π∗ bands appear at 370 nm and 456 nm, respectively, at a concentration of 5 × 10−6 M. This is in support of the hypothesis of trans-to-cis-isomerisation with lowering of concentration. DFT calculations are shown.