4,5,5-Trimethyl-2,5-dihydrofuran-Based Electron-Withdrawing Groups for NIR-Emitting Push–Pull Dipolar Fluorophores

In
the context of molecular engineering of push–pull dipolar
dyes, we introduce a structural modification of the well-known electron-accepting
group 2-dicyanomethylidene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran
(TCF). Introduction of a (benzo­[d]­thiazol-2-yl)
moiety failed, and unexpected structures were obtained. On the other
hand, phenylthio and phenylsulfonyl entities were successfully introduced
at position 3 of the 2-(dicyanomethylidene)-2,5-dihydrofuran ring,
giving access to new electron-acceptor groups and dipolar fluorophores
displaying near-infrared emission in solution or in the solid state,
brighter than their TCF analogues.