Dramatically Enhanced and Red-shifted Photoluminescence Achieved by Introducing an Electron-withdrawing Group into a Non-traditional Luminescent Small Organic Compound.

Small organic compounds without any traditional fluorescent chromophores are generally non-emissive, and only very a few are reported to emit weak blue fluorescence. Here we synthesize a non-traditional luminescent small organic compound N-(2,2,2-trifluoroethyl)acrylamide (TFAM) with dramatically enhanced and red-shifted photoluminescence by introducing a strong electron-withdrawing group into acrylamide (AM). Very impressively, TFAM emits cyan (472 nm) and yellow-green (560 nm) fluorescence in solutions and solid state, respectively. TFAM also shows aggregation-induced emission enhancement (AIEE) and excitation-dependent fluorescence (EDF) characteristics, as well as temperature and metal cations-responsive fluorescence. Theoretical calculations show that the introduction of electron-withdrawing group leads to a lower energy gap between the HOMO-LUMO energy levels in TFAM than in AM. And strong cooperative hydrogen bonds are formed in TFAM molecules, resulting in rigidification of molecular conformations. The study provides a strategy for preparing non-traditional luminescent compounds with enhanced and red-shifted photoluminescence.