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

J Org Chem. 2019 Aug 16;84(16):9965-9974. doi: 10.1021/acs.joc.9b01120. Epub 2019 Aug 1.

Abstract

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.