Studies on the charge-transfer complexes of o-chloranil with a series of methylbenzenes

Equilibria for the formation of molecular electron-donor-acceptor (EDA) com plexes of a series of methylbenzenes with o-chloranil have been studied in CCl4 medium. The charge transfer (CT) transition energies are found to chan ge systematically with change in the number and positions of methyl groups in the donor molecule (methylbenzenes). This is well interpreted by the sim ple PMO theory. Semiempirical AMI and PM3 calculations have been done on th e EDA complexes considering them as supermolecules. The lowest S-1<--S-0 tr ansition is clearly shown to be associated with the transfer of one electro n from the donor to the acceptor moiety in the excited state, while practic ally no change transfer occurs in the corresponding ground state. The theor etical CT transition energies follow the same trend as that observed from e xperimental values.