Organic thermally activated delayed fluorescence (TADF) materials are emerging as potential candidates for time-resolved fluorescence imaging in biological systems. However, the development of purely organic TADF materials with bright aggregated-state emissions in the red/near-infrared (NIR) region remains challenging. Here, we report three donor-acceptor-type TADF molecules as promising candidates for time-resolved fluorescence imaging, which are engineered by direct connection of electron-donating moieties (phenoxazine or phenothiazine) and an electron-acceptor 1,8-naphthalimide (NI). Theoretically and experimentally, we elucidate that three TADF materials possessed remarkably small ΔEST to promote the occurrence of reverse intersystem crossing (RISC). Moreover, they all exhibit aggregation-induced red emissions and long delayed fluorescence lifetimes without the influence of molecular oxygen. More importantly, these long-lived and biocompatible TADF materials, especially the phenoxazine-substituted NI fluorophores, show great potential for high-contrast fluorescence lifetime imaging in living cells. This study provides further a molecular design strategy for purely organic TADF materials and expands the versatile biological application of long-lived fluorescence research in time-resolved luminescence imaging.
Bibliographical noteFunding Information:
This study was supported by grants from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIP) (no. 2012R1A3A2048814 for J.Y., no. 2019R1A6A1A11044070 for S.P. and 2020R 1A 6C 101B194 for S.-J.K.). FAB mass spectral data were obtained from the Korea Basic Science Institute (Daegu) on a Jeol JMS 700 high-resolution mass spectrometer.
© 2020 American Chemical Society.
- aggregation-induced emission
- fluorescence imaging
- red emission
- thermally activated delayed fluorescence (TADF)
- time-resolved luminescence imaging