Benzothiophene-TCNQ

Attempts to increase the dimensionality by means of interstack sulphur-sulphur contacts led to the synthesis of other TCNQ analogues of thiophene. Thus, the thiophene-TCNQ (23) [46] and its vinilogue (24) [48] were prepared and, more recently, the benzothiophene-TCNQ (25) and its vinilogue (26) as the first electron acceptors derived from isothianaphthene were synthesized [49]. 

A similar analysis has been done91 on CT-complexation of the series benzene, benzothiophene, benzo[l,2-b, 4,3-b ]dithiophene ([3]SBS), and the homologs [5]SBSBS and [7]SBSBSBS with TCNQ as the acceptor. Beside association constants, also AH- and AS-values were determined by measurements at different temperatures (Table 21). It is striking that the gradual increase of the association constant in the series is interrupted at [5]SBSBS the next member has even a lower value. 

The half-wave redox potentials of the novel acceptors are summarized in Table 1.2 and, in general, possess a considerably weak accepting ability compared with that of TCNQ. However, the presence of bromine atoms on the central thienoquinoid ring allows the tuning of the acceptor strength. The single-crystal X-ray analysis of benzothiophene (25) showed the interesting feature of a planar molecule. 

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