Synthesis and study of radical cation salts and TCNQ charge transfer complexes of a series of tetrathiafulvalenes (TTF) substituted by one or two hydroxylated side chain(s): –SCH2CH2OH

Abstract

Unsymmetrically substituted tetrathiafulvalene derivatives containing hydroxy group(s) on side-chain(s) have been synthesized from cyano precursors via either a cross-coupling reaction or a Wittig-type condensation. As deduced from cyclic voltammetry data, the electron donor properties of the obtained compounds have been found to be similar to those of BEDTTTF. A series of radical cation salts derived from these donors has been obtained by electrocrystallization and charge transfer complexes have been prepared chemically by using TCNQ as an electron acceptor. The electrical conductivity of these phases ranges from 3 × 10−2 to 7 × 10−7 S cm−1 which is consistent with their structural features. X-Ray structural analysis of three of the radical cation salts with monovalent closed-shell anions (Br−, ClO4−) indicates a 1 ∶ 1 stoichiometry which implies that, in each case, the donor has been oxidized to the D+ state. In the same way, a crystal structure made of stacks where the donor and the acceptor molecules alternate has been found for a charge transfer complex between TCNQ and a donor derived from EDTTTF. The crystal structure of one of the donors indicates that the flexibility of the hydroxylated side chains appears as a favourable feature for the formation of hydrogen bonds.