Tris[oligo(1,4‐phenylenevinylene)]methylium Dyes

Abstract

AbstractThe tris[oligo(1,4‐phenylenevinylene)]carbinols 2a–f (n =1–4) and the tris(4‐styrylphenyl)methanes 7a,b have been prepared by Wittig–Horner (3 + 4a–f → 2a–f) and Siegristreactions (5 + 6a,b → 7a,b). The Wittig–Horner reactions in these examples are accompanied by an autoxidation, whereas a reduction occurs in the Siegrist reactions. Compound 2a, the lowest member (n = 1) of the series 2a–d with terminal dialkylamino groups, generates first, on treatment with acids, the methylium dye 2′a, which absorbs far into the NIR region (λmax = 1100 nm). The higher members 2b,c (n = 2,3) of the carbinol series yield by acidic treatment only N‐protonated methylium dyes 2″′b,c. The different behavior is due to a decreasing donor–acceptor interaction with increasing D–A distance. The N‐protonated methylium salts 2″′a–c show long‐wavelength absorptions in the region of the Vis/NIR border. Their values apporach, for increasing numbers n of repeat units, λ∞ = 877 nm. The structures and possible push–pull effects of the salts 2′a and 2″′a–c were studied by NMR and UV/Vis/NIR spectroscopy and compared with the selected model compounds 2e and 7a. The results shed new light on previously published triphenylmethane dyes with extended conjugation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)