The synthesis, Langmuir-Blodgett (LB) deposition and charge-transfer spectra of Z-/3-(l-alkyl-4-quinolinium)-acyano-4styryldicyanomethanide (R-Q3CNQ where R = C&i 1 to CzoH41) and four substituted analogues are described. The deposition is Z-type and the properties are dependent upon the hydrophobic chain length. C6H13-Q3CNQ to C14H,,-Q3CNQ form green LB films (A,,, = 614 4 nm; HWHM = 37 k 2 nm) !nd occupy 2&34 A' per molecule at 25 mN m -" . In contrast, Cl,H3,-Q3CNQ to C2,H,,-Q3CNQ occupy 40-50 A' per molecule; their films are purple with A , , , = 565 k 4 nm and HWHM = 22 & l nm. The shift is attributed to a change in molecular tilt which causes the transition to alter from an intermolecular to an intramolecular process. Multilayer films of C, ,H3,-Q3CNQ exhibit strong second-harmonic generation (SHG) and the intensity increases quadratically with the number of LB layers.

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The single crystal conductivity of (N,N'-dimethyl-4,4'-bipyridinium)2+(7,7,8,8-tetracyanop- quinodimethanide)32-, DMBP-TCNQ3, exhibits an anomaly at 170 K which may be attributed to a phase transition and, also, a change in activation energy at 135 K which may be attributed to the onset of extrinsic behaviour. Above 135 K the conductivity varies as σ = σ0 exp(-E2/kT) where σ300K. = 1 S cm-1 and Ea = 0.18 eV. In the high temperature region the thermoelectric e.m.f. saturates to a temperature independent value of S = - 20 μVK-1 whereas for the related monoquaternised salt, [N-phenyl-4-(4'-pyridyl)-pyridinium]+(TCNQ)2-, ØBP-TCNQ2, S = - 55 μVK-1. The thermoelectric data may be interpreted in terms of the Chaikin and Beni model and the results indicate 92% charge transfer in DMBP-TCNQ3 and 100% charge transfer in 0BP-TCNQ2.