Solvent induced fluorescence of 9-chloro-10,10′-bis(dichloromethyleno)-(9′H)-10,10′-dihydro-9,9′-bianthryl (CDDB): twisted intramolecular charge transfer process

Abstract

Solvent polarity induced fluorescence of 9-chloro-10,10′-bis(dichloromethyleno)-(9′H)-10,10′-dihydro-9,9′-bianthryl (CDDB) is studied in a series of homologous alcohols from methanol to pentanol and compared with the previously reported data for CDDB microcrystal and CDDB in cyclohexane. In microcrystal, the locally excited (LE) state and in non-polar solvents, intramolecular charge transfer (ICT) state are mainly responsible for fluorescence. In polar solvents, it has been proposed from the computed decomposed spectra that polarity dependent twisted intramolecular charge transfer (TICT) state also gives fluorescence along with ICT state fluorescence. The process has been discussed as per a proposed scheme. Formation of TICT state has been further confirmed from the measurement of equilibrium constants between ICT and TICT states in homologous alcohols and by analysing the kinetics of radiative and non-radiative pathways of individual ICT and TICT components. The formation mechanisms of ICT and TICT states are discussed on the basis of solvent induced change in molecular forms and charge separation due to rotation of the two moieties of CDDB along the C 9-C 9′ bond.