Journal
ACS ENERGY LETTERS
Volume 2, Issue 7, Pages 1526-1533Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsenergylett.7b00268
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Funding
- Dow Chemical Company [244699]
- National Science Foundation Graduate Research Fellowship [DGE 1106400]
- Philomathia Foundation Postdoctoral Fellowship
- Department of Energy Graduate Research Fellowship [DE-AC05-060R23100]
- Alfred P. Sloan Research Fellowship
- David and Lucile Packard Foundation Fellowship for Science and Engineering
- Camille and Henry Dreyfus Teacher Scholar Award
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
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Solid-state solvation (SSS) is analogous to liquid-phase solvation but occurs within glassy matrices. Organic solutes with singlet charge transfer ((CT)-C-1) excited states are especially susceptible to solvatochromism. Their (CT)-C-1 states and photon emission energies decrease when surrounding molecules with sterically unhindered polar moieties reorient to stabilize them. Thermally activated delayed fluorescence (TADF) organic light-emitting diodes feature such solutes as emitters in the solid state, employing efficient reverse intersystem crossing to harvest the majority of electrogenerated triplets. Here we explore the potential of SSS to manipulate not only these emitters' (CT)-C-1 states but also, concurrently, their singlet-triplet energy gaps (Delta E-ST) that control TADF. By solvating the TADF emitter 2PXZ-OXD with progressively increasing concentrations of camphoric anhydride (CA) in a polystyrene film, we find that it is possible to finely tune the emitter's photophysics. We observe a maximum increase in prompt lifetime and corresponding decrease in delayed lifetime of similar to 60%. By contrast, the photoluminescence quantum yield peaks at an intermediate CA concentration, reflecting competition between increasing reverse intersystem crossing yield and decreasing singlet oscillator strength. Our findings demonstrate technologically relevant fine control of emitter photophysical properties, as varying the extent of SSS reveals the convolved evolution of different kinetic rates as a function of the (CT)-C-1 state energy and Delta E-ST.
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