Synthesis and properties of π-conjugated dithiafulvene oligomers by addition of a monofunctionalized compound

Dithiafulvene oligomers (3) were prepared by cycloaddition polymerization of aldothioketenes with their alkynethiol tautomers derived from 1,4‐diethynylbenzene (2) with the addition of 1‐ethynyl‐4‐methylbenzene (1) as a monofunctionalized compound. Different feed ratios of 2/1were used to control the molecular weights of 3. The structures of 3 were confirmed by IR and 1H NMR spectroscopies in comparison with those of 2‐(4‐tolylidene)‐4‐tolyl‐1,3‐dithiol (4) as a model compound, which was obtained by the treatment of lithium 2‐tolylethynethiolate with water in Et2O. The number‐average degree of polymerization (DP) and the number‐average molecular weight were measured by gel permeation chromatographic and 1H NMR analysis. DP increased with an increasing feed ratio of 2/1. The ultraviolet–visible spectra of 3 in diluted acetonitrile showed that the absorption maxima of 3 increased with an increasing DP of 3. These redshifts are ascribed to an effective expansion of the π‐conjugation system in 3. The oligomers exhibited a maximum conjugation length of seven repeating units. The redox properties of 3 were examined by cyclic voltammetry. The oxidation half‐peak potentials (Ep/2) of 3 were slightly cathodically shifted with increasing DP. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 708–715, 2003 Dithiafulvene oligomers (3) were prepared by cycloaddition polymerization of aldothioketenes with their alkynethiol tautomers derived from 1,4‐diethynylbenzene (2) with the addition of 1‐ethynyl‐4‐methylbenzene (1) as a monofunctionalized compound. The structures of 3 were confirmed by IR and 1H NMR spectroscopies. Gel permeation chromatographic and 1H NMR analysis suggested that the number‐average degree of polymerization (DP) increased with an increasing feed ratio of 2/1. The ultraviolet–visible spectra of 3 demonstrated that the absorption maxima of 3 increased with increasing DP. These redshifts are ascribed to an effective expansion of the π‐conjugation system in 3. The oligomers exhibited a maximum conjugation length of seven repeating units. The oxidation half‐peak potentials (Ep/2) of 3 were cathodically shifted with increasing DP.