SEMICONDUCTING LANGMUIR-BLODGETT-FILMS OF ETHYLENEDITHIOTETRATHIAFULVALENE (EDT-TTF) DERIVATIVES BEARING CHARGED AND UNCHARGED AROMATIC SUBSTITUENTS

Ethylenedithiotetrathiafulvalene (EDT-TTF) derivatives 1-4 functionali sed with a single aromatic ring have been synthesised and their Langmu ir-Blodgett (LB) films have been assembled utilising only 25% molar ra tio of fatty acid. For compounds 1, 3 and 4, predominantly Y-type depo sition onto solid supports was observed with a transfer ratio close to unity. After doping with iodine vapour, the maximum in-plane conducti vity values obtained were sigma(rt) = 10(-3) S cm(-1) for 1 and 3, and 10(-5) S cm(-1) for 4. LB deposition of 2 was not uniform and the con ductivity value after doping was low. UV-VIS spectra of the LB films r eveal the appearance of a charge-transfer (CT) band at lambda(max) = c a. 900 nm for 1 and 4 after iodine doping. A solution of compound 3 ex hibited a weak absorption band at cu. 665 nm which is assigned to an i ntramolecular CT band; the intensity of this band increases on exposur e of the solution to light. This band is not observed in LB films of 3 , neither as-deposited nor after doping. Molecular orbital calculation s indicate that in the minimum energy conformation of 3, the pyridiniu m moiety is practically orthogonal to the TTF unit and this conformati on may be obtained in solution, enabling charge-transfer to occur. A m ore linear conformation of 3 in the LB films may prevent intramolecula r charge-transfer from occurring. Monolayers of 1, 3 and 4 were charac terised by cyclic voltammetry which revealed two redox steps consisten t with the formation of the EDT-TTF cation radical and dication, respe ctively.