Endothermic and Exothermic Energy Transfer Made Equally Efficient for Triplet–Triplet Annihilation Upconversion

Abstract

Expanding the anti-Stokes shift for triplet−triplet annihilation upconversion (TTA-UC) systems with high quantum yields without compromising power density thresholds (I th ) remains a critical challenge in photonics. Our studies reveal that such expansion is possible by using a highly endothermic TTA-UC pair with an enthalpy difference of +80 meV even in a polymer matrix 1000 times more viscous than toluene. Carrying out efficient endothermic triplet−triplet energy transfer (TET) requires suppression of the reverse annihilator-to-sensitizer TET, which was achieved by using sensitizers with high molar extinction coefficients and long triplet state lifetimes as well as optimized annihilator concentrations. Under these conditions, the sensitizer-toannihilator forward TET becomes effectively entropy driven, yielding upconversion quantum yields comparable to those achieved with the exothermic TTA-UC pair but with larger anti-Stokes shifts and even lower I th , a previously unattained achievement.

Indirect Red and Near-Infrared Z-to-E Photoisomerization of ortho-Functionalized Azobenzenes via Triplet Energy Transfer

“…14,17,18 Based on the isomerization kinetics, even endothermic TET (as is the case with FPA) is apparently capable of driving isomerization efficiently. This indicates that the whole process of triplet-sensitized isomerization is largely entropy-driven 33,34 , since the rate of the isomerization is fairly decoupled from the change in enthalpy involved in TET. The ).…”

“…This also effectively eliminates the azobenzene-to-sensitizer reverse TET. 34 Therefore, even photosensitizers with considerably lower triplet energies are still capable of sensitizing the Z-to-E isomerization of azobenzenes, which enables the expansion of excitation wavelengths to deeper red and even into NIR.…”

Expanding excitation wavelengths for azobenzene photoswitching into the near-infrared range via endothermic triplet energy transfer

“…26,29,49 Based on the isomerization kinetics, even endothermic TET (as is the case with FPA) is apparently capable of driving isomerization efficiently. This indicates that the whole process of triplet-sensitized isomerization is largely entropy-driven, 51,52 since the rate of the isomerization is fairly decoupled from the change in enthalpy involved in TET. The change in entropy (DS) of TET is 51…”

In silico prediction of annihilators for triplet–triplet annihilation upconversion via auxiliary-field quantum Monte Carlo

“…We comment that endothermic entropically-driven, endothermic TET has previously been reported in the literature. 9,90,91 In these representative instances, TET is found to be up-hill by <0.1 eV, which is a signicantly smaller number than the smallest TDDFT-predicted endothermicity of PtOEP/Ph-BTD, which is 0.25 eV (B3LYP). This very extreme endothermicity, in light of literature precedent, most likely would not allow forward TET.…”