Degree of charge transfer in the mixed stack donor-acceptor charge transfer complex of C18 TCNQ and TMB probed by laser Raman spectroscopy

This paper essentially is a study and confirmation of charge transfer between the 3,3',5,5'-tetrabenzidine and 2-octadecyl 7,7,8,8-tetracyanoquinodimethane (TMB- C(18)TCNQ) by Raman scattering technique oil a cast film of the sample. Organic charge transfer complexes composed of planar aromatic donor (D) and acceptor (A) molecules have been recognized to be of crucial importance due to their unique physical properties which arise from their low dimensionality A cast film of 2-octadecyl-7.7,8.8 tetracyanoquinodimethane (C(18)TCNQ) was prepared on a gold coated glass slide and its Raman spectrum was studied using excitation lines from a He-Cd laser (441.6 nm). The cast film of C(18)TCNQ was then doped with 3,3',5,5' -tetramethylbenzidine (TMB) which resulted in the change of colour from yellow to purple-red. The shift in the position of the bands in the Raman spectrum of this doped sample revealed the formation of a charge transfer complex. The Raman bands of the pure C,,T(18)TCNQ sample at 14-43 cm(-1) and 2219 cm(-1) were shifted to 1423 cm(-1) and 2203 cm(-1) respectively, after doping with TMB. From a detailed study of these bands, the degree of charge transfer (r) from C(18)TCNQ to TMB has been estimated.