Furan-π-EWG skeleton for narrowband NIR-emissive fluorescent dyes†
Abstract
A novel D–π–A type skeleton of vinyl-bridged furan/thiophene and an electron-withdrawing group (FVW/TVW) was developed, and showed narrowband-emissive near-infrared (NIR) fluorescence. In particular, dimethylamino-furan/thiophene-π-isophoryl-malononitrile (TV-IM and FV-IM) with low molecular weights of 323 and 307 exhibited large Stokes shifts of 112 nm and 74 nm and NIR-I emissions at 716 nm and 730 nm with narrowband emission with full width at half maxima of 33 nm and 37 nm, respectively. The narrowband emissions of the FVW and TVW dyes were primarily attributed to their rigid and conjugated D–π–A skeleton and heavy-atom effect of sulfur and could be further attributed to the segregated and alternated positive and negative phases of their HOMO and LUMO orbitals in ground (S0) and excited states (S1). Moreover, the narrowband NIR-emissive TVW dyes were successfully used to monitor viscosity and fabricate fluorescent polymeric nanofiber films.