A. Ishii, Shota Kobayashi, Yuta Aoki
Nov 1, 2014
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Journal
Heteroatom Chemistry
Abstract
3-Methylene-2,3-dihydrothienothiophene and -selenophenothiophene derivatives incorporated in a rigid dibenzobarrelene skeleton were synthesized by intramolecular Diels–Alder reaction, and their structures, fluorescent properties, and electrochemistry were elucidated. In 3-methylene-2,3-dihydrothieno[3,2-b]thiophene derivatives, silyl and phenyl substituents at the terminal position were effective for strong blue fluorescence (λem = 412–455 nm) with high quantum yields (ΦF = 0.65–0.99), whereas the unsubstituted parent compound was weakly fluorescent (λem = 338 nm, ΦF = 0.03). The phenyl-substituted [3,2-b]-derivative showed strong emission also in the solid state (ΦF = 0.70). The corresponding [2,3-b]-isomer showed blueshifted absorption (λabs = 342 nm) and emission (λem = 436 nm) maxima with low-to-moderate quantum yields in solution (ΦF = 0.24) and in the solid state (ΦF = 0.41). In the case of the selenium congeners (3-methylene-2,3-dihydroselenopheno[3,2-b]thiophene derivatives), the heavy atom effect due to the selenium was decisive to decrease the quantum yields (ΦF = 0.01–0.06). The oxidation of phenyl-substituted [3,2-b]-derivative yielded the corresponding sulfoxide and sulfone, which showed strong emission at around 440 nm with high quantum yields in dichloromethane (ΦF = 0.91 and 0.98, respectively). A dimer of the phenyl-substituted [3,2-b]-derivative was prepared by oxidative coupling of the lithio derivative. The dimer had weak redshifted emission (λem = 547 nm, ΦF = 0.10) and showed a reversible cyclic voltammogram with E1/2 = 0.35 V versus Fc/Fc+ redox couple.