GIANT ANALOGS OF TETRATHIAFULVALENE IN LANGMUIR AND LANGMUIR-BLODGETT-FILMS

The behaviour of new giant tetrathiafulvalene (TTF) analogues has been studied at the gas/water interface and in Langmuir-Blodgett films. Th ese compounds, denoted G-TTFCn, have a dihydro-TTF core which bears tw o conjugated side-arms with various alkyl chains (from methyl to octyl ). Langmuir films of these compounds are quite stable versus time and are characterized by a collapse pressure that increases as the length of the alkyl chains decreases. The ability of these compounds to form Langmuir films should then be due to their extended TTF core. Except f or G-TTFC1, transfer of the monolayer onto a solid substrate is easily done at low surface pressure. Doping of the LB films by iodine vapour s changes their spectroscopic (EPR, electronic and vibrational) behavi our and leads to rather poor conducting films. Conductivity of G-TTFC4 films (sigma(RT)approximate to 4 x 10(-7) S cm(-1)) is two orders of magnitude lower than for G-TTFC2 (sigma(RT)approximate to 4 X 10(-4) S cm(-1)), showing the influence of the molecular packing on the electr ical properties of such films. Different results are obtained upon mix ing these G-TTFCn compounds with pentadecyltetracyanoquinodimethane (C (15)TCNQ) in various proportions, which gives rise to charge transfer complexes of adjustable stoichiometry. It is shown that these extended pi-donor molecules give new insights on the redox processes that can lead to conducting films.