Long-wavelength chromophores with thermally activated delayed fluorescence based on fluorescein derivatives

Long-wavelength chromophores are developed based on fluorescein derivatives by introducing a strong acceptor 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene) malononitrile (TFM). By changing the number of TFM, we obtained two chromophores, which are named DTFM-DCF and STFM-DCF, respectively. Due to the large, rigid π-conjugated structure and strong electron-withdrawing capability of TFM, the maximum emission wavelengths of these molecules span from 681 to 755 nm in dichloromethane. Meanwhile, these two chromophores, which exhibit the property of thermally activated delayed fluorescence, have long-lived luminescence with 9.02 μs for STFM-DCF and 0.43 μs for DTFM-DCF in deaerated dichloromethane at room temperature.