Thiophene-Fused 3-Methylene-2,3-dihydrochalcogenophenes: Fluorescent Dyes Incorporated in a Rigid Dibenzobarrelene Skeleton

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 (lambda(em) = 412-455 nm) with high quantum yields (Phi(F) = 0.65-0.99), whereas the unsubstituted parent compound was weakly fluorescent (lambda(em) = 338 nm, Phi(F) = 0.03). The phenylsubstituted [3,2-b]-derivative showed strong emission also in the solid state (Phi(F) = 0.70). The corresponding [2,3-b]-isomer showed blueshifted absorption (.abs = 342 nm) and emission (lambda(em) = 436 nm) maxima with low-to-moderate quantum yields in solution (Phi(F) = 0.24) and in the solid state (Phi(F) = 0.41). In the case of the selenium congeners (3-methylene2,3-dihydroselenopheno[3,2-b] thiophene derivatives), the heavy atom effect due to the selenium was decisive to decrease the quantum yields (Phi(F) = 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 (Phi(F) = 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 (lambda(em) = 547 nm, Phi(F) = 0.10) and showed a reversible cyclic voltammogram with E-1/2 = 0.35 V versus Fc/Fc(+) redox couple. (C) 2014 Wiley Periodicals, Inc.