Dopant-Matrix Afterglow Systems: Manipulation of Room-Temperature
Phosphorescence/Thermally Activated Delayed Fluorescence Afterglow
Mechanism via Mismatch/Match of Intermolecular Charge Transfer between
Dopants and Matrices
Dopant-matrix organic afterglow materials
exhibit ease of fabrication
and intriguing functions in diverse fields. However, a deep and comprehensive
understanding of their photophysical behaviors remains elusive. Here
we report manipulation of a room-temperature phosphorescence/thermally
activated delayed fluorescence (RTP/TADF) afterglow mechanism via
the mismatch/match of intermolecular charge transfer between dopants
and matrices. When dispersed in inert crystalline matrices, the luminescent
dopants show RTP lifetimes up to 2 s. Interestingly, when suitable
organic matrices are selected, the resultant dopant-matrix materials
display a TADF-type afterglow under ambient conditions due to the
formation of dopant-matrix intermolecular charge transfer complexes.
Detailed studies reveal that reverse intersystem crossing from dopants’
T1 states to charge transfer complexes’ S1 states, which features a moderate kRISC of 101–102 s–1, is
responsible for the emergence of a TADF-type organic afterglow in
rigid crystalline matrices. Such less reported delicate photophysics
reveals a new aspect of the excited state property in dopant-matrix
afterglow systems.