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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 (1CT) excited states are especially susceptible to solvatochromism. Their 1CT 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’ 1CT states but also, concurrently, their singlet–triplet energy gaps (ΔE 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 ∼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 1CT state energy and ΔE ST.

Solid-state solvation (SSS) is a solid-state analogue of solvent-solute interactions in the liquid state. Although it could enable exceptionally fine control over the energetic properties of solid-state devices, its molecular mechanisms have remained largely unexplored. We use ultrafast transient absorption and optical Kerr effect spectroscopies to independently track and correlate both the excited-state dynamics of an organic emitter and the polarization anisotropy relaxation of a small polar dopant embedded in an amorphous polystyrene matrix. The results demonstrate that the dopants are able to rotationally reorient on ultrafast time scales following light-induced changes in the electronic configuration of the emitter, minimizing the system energy. The solid-state dopant-emitter dynamics are intrinsically analogous to liquid-state solvent-solute interactions. In addition, tuning the dopant/polymer pore ratio offers control over solvation dynamics by exploiting molecular-scale confinement of the dopants by the polymer matrix. Our findings will enable refined strategies for tuning optoelectronic material properties using SSS and offer new strategies to investigate mobility and disorder in heterogeneous solid and glassy materials.

Chemical shifts (6) in p.p.m., coupling constants in Hz. Measurements at ambient temperatures. Measured in CD,Cl,. Proton resonances for the BH groups occur as broad unresolved signals in the range 6 0-3. Hydrogen-1 decoupled, chemical shifts are positive to high frequency of SiMe,, with measurements in CD,CI,-CH,C1,. Peaks for minor isomer, other signals obscured by signals for major isomers. Signal for POMe group obscured by solvent peak. Peaks for major isomer. is likely to be present in (8a) also, since the p-C resonances in the 'C-{ ' H} n.m.r. spectra of the two complexes are so similar and are close to that observed (6 293.8 p.p.m.) for the terminal M o X group in (7). In dimetal complexes with bridging alkylidyne groups the signals for the p-C nuclei are generally significantly more deshielded than 300 ~. p . m . ~~. ~ Compound (8a) appears to be more stable than (8b). In the synthesis of the latter a by-product was the salt [N(PPh,),]-[W2Au(p-CC6H4Me-4)2(CO)4(q5-C2B9H9Me2)2], formed by displacement of the PPh, group in (8b) by the CrW moiety of (lc). No similar trimetal species was observed to form in the reaction between [AuCI(PPh,)] and (7). The reaction between (7) and [Rh(cod)(PPh,>,][PF,] in CH2C1, afforded the compound [MoRh(p-CC6H4Me-4)(p-CO){ P(OMe),}(PPh,),(q5-C,B,H,Me2)] (9a), data for which are summarised in Tables 1-3. The related tungsten-rhodium compound [WRh(p-CC6H4Me-4)(p-CO)(CO)(co)(PPh3)2(q5-c2~ B,H,Me,)] (9b) has been prepared by treating the [N(PPh,),] salt of (lc) with [RhCl(PPh,),] or [Rh(cod)(PPh3),][PF6]. An X-ray diffraction study revealed that it contained a strongly