Abstract
Time-resolved emission spectra of thermally activated delayed fluorescence (TADF) compounds in solid hosts demonstrate significant temporal shifts. To explain the shifts, two possible mechanisms were suggested, namely, slow solid-state solvation and conformational disorder. Here we employ solid hosts with controllable polarity for analysis of the temporal dynamics of TADF. We show that temporal fluorescence shifts are independent of the dielectric constant of the solid film; however, these shifts evidently depend on the structural parameters of both the host and the TADF dopant. A ≤50% smaller emission peak shift was observed in more rigid polymer host polystyrene than in poly(methyl methacrylate). The obtained results imply that both the host and the dopant should be as rigid as possible to minimize fluorescence instability.
Highlights
Time-resolved emission spectra of thermally activated delayed fluorescence (TADF) compounds in solid hosts demonstrate significant temporal shifts
The most efficient organic light-emitting diode (OLED) devices are made of emissive thermally activated delayed fluorescence (TADF) compounds.[1−3] The high emission yield of TADF compounds is achieved by minimizing the singlet− triplet energy gaps (ΔEST) and enabling thermally activated reverse intersystem crossing of triplet states.[4,5]
A lower ΔEST is achieved by minimizing the electron exchange energy, which depends on the HOMO−LUMO overlap.[9]
Summary
Time-resolved emission spectra of thermally activated delayed fluorescence (TADF) compounds in solid hosts demonstrate significant temporal shifts. Most of the studies analyzing the temporal behavior of solid-state TADF are performed in different hosts, based on either polymer or small-molecule compounds.[15,22,24] various host materials differ in more than one parameter.
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