Vibrational spectra of CT complexes of acridine orange

Abstract

Infrared spectra of acridine orange and its charge transfer complexes with acceptors such as chloranil, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and tetracyano-p-ethylene (TCNE) are reported here. Their photo conducting nature is explained with two absorption edges in infrared range associated with non-equivalent sites of chloride ion or formation of bonding, non-bonding and antibonding orbitals. The mid-IR transition is usually direct and the low-energy transition is indirect. Whether the transition is allowed or forbidden depends on average intermolecular distance. This differs from ordinary ternary complexes in which two acceptors give rise to two conduction bands. Also, there is absence of any screening found in two donor based ternary systems. There is some band tailing of phonon bands in absorption function above Eℊ. Only TCNQ and TCNE complexes show weak Gaussian bands below 800 cm⁻¹. The repetitions of structures associated with the oscillations in the density of states are found which reveal that these CT complexes can work as molecular multi-vibrators.