Research On The Fluorescein Derivate With Thermally Activated Delayed Fluorescence

Thermally activated delayed fluorescence (TADF) luminescent materials have attracted considerable attention because of the potential high quantum efficiency achieved via the reverse intersystem crossing process (RISC). It possessed potential application in OLED and bioimaging. However it's still unclear on the luminous mechanism of TADF and the related influencing factors which hindered the further application.In this work, we introduced aromatic ketones such as acetophenone and thienone to synthesize fluorescein derivates C-1,C-2, on the basis of our previous delayed fluorescence compound. To confirm the generation of triplet excited states, nanosecond transient absorption spectroscopy were carried out, C-1,C-2 showed microsecond time scale long-lived triplet. We measured the time-resolved photoluminescence with and without N2 bubbling to confirm the generation of delayed fluorescence. By comparing the normalized steady-state fluorescence spectrum with time-resolved fluorescence spectrum, the emission around 590 nm contains a prompt fluorescence component (PF) and a delayed fluorescence component (DF). We measured the fluorescence lifetime in the nanosecond time scale for PF and in the microsecond time scale for DF, the lifetime of delayed fluorescence is more sensitive to oxygen. We measured the decay rate of DF dependent on temperature and fitted on double exponential to acquire the energy gap between the singlet and triplet states (? EST) for C-1(34.58 mev) and C-2 (25.96 mev).This energy gap was small enough to result in reverse ISC and realize efficient TADF.In all, we designed and synthesized new structure of fluorescein derivates. By researching the photophysical properties, we elucidated the relationship between structure and property of our new TADF molecules. Also the extended long-lived triplet and delayed fluorescence lifetime laid the foundation for better application on time-resolved luminescence imaging measurement.