Comparison of the structure property relationships in LB films of zwitterionic TCNQ adducts

Substitution reactions of TCNQ (7,7,8,8-tetracyanoquinodimethane) with suitable quinolinium and picolinium electron donor moieties yielded an extensive analogous series of alpha-bridged quinolinium and picolinium adducts R(2)Q3CNQ and R(2)P3CNQ respectively of which the long chain (Z)-{(beta-[N-(1-hexadecyl)quinolinium-2-yl]-alpha-cyano-4-styryl}-dicyanome thanide (C16H33(2)Q3CNQ) is a typical example. These zwitterionic D-pi-A materials (where D and A are electron donor and acceptor respectively) exhibit properties such as solvatochromism, molecular rectification and second harmonic generation and were compared and contrasted to the existing y-bridged adducts. The behaviour of the materials on the water subphase and their resultant Langmuir-Blodgett (LB) film fabrication were studied. The abrupt change in molecular orientation in LB films of the gamma-bridged adducts occurring at R = C15H31 and above was not seen in the more flatly orientated alpha-bridged adducts. Further characterisation of the LB films was performed using reflectance-absorption infra-red spectroscopy (RAIRS) and surface plasmon resonance (SPR). The crystal structure of the long chain adduct, C10H21(2)Q3CNQ, is also reported.