The synthesis and characterisation of Langmuir-Blodgett film forming TCNQ adducts.

Substitution reactions of TCNQ (7,7,8,8-tetracyanoquinodimethane) with suitable electron donor moieties extended the range of gamma-bridged adducts R(4)Q3CNQ and R(4)P3CNQ of which the short chain Z-beta-(l-butyl-4'-quinolinium)-alpha-cyano-4-styryldicyanomethanide (C[4]H[9](4)Q3CNQ) is a typical example. These zwitterionic D-pi-A materials (where D and A are electron donors and acceptors respectively) exhibit properties such as solvatochromism, molecular rectification and second harmonic generation. Further synthetic work concentrated on modifying the donor, the acceptor and the substitution position within these zwitterions to create a series of diverse materials for non-linear optic research. Modification of the picolinium and quinolinium systems where the TCNQ substitution is in the alpha-position, has created the extensive analogous series-R(2)Q3CNQ and R(2)P3CNQ, their properties being compared and contrasted to the original gamma-bridged adducts. The behaviour of the materials on the subphase and their resultant Langmuir-Blodgett (LB) film fabrication was studied. The abrupt change in molecular orientation in LB films of the gamma-bridged adducts occurring at R= C[15]H[31] and above was not seen in the more flatly orientated alpha-bridged adducts. Further characterisation of the LB films was performed using reflectance-absorption infrared spectroscopy (RAIRS) and surface plasmon resonance (SPR).A number of N-alkylpyridinium benzimidazolate betaine derivatives and the related betaine-TCNQ adducts were prepared and their LB film forming properties were studied.