Approaching the Spin-Statistical Limit in Visible-to-Ultraviolet Photon Upconversion

Abstract

Triplet–triplet annihilation photon upconversion (TTA-UC) is a process in which triplet excitons combine to form emissive singlets and holds great promise in biological applications and for improving the spectral match in solar energy conversion. While high TTA-UC quantum yields have been reported for, for example, red-to-green TTA-UC systems, there are only a few examples of visible-to-ultraviolet (UV) transformations in which the quantum yield reaches 10%. In this study, we investigate the performance of six annihilators when paired with the sensitizer 2,3,5,6-tetra(9 H -carbazol-9-yl)benzonitrile (4CzBN), a purely organic compound that exhibits thermally activated delayed fluorescence. We report a record-setting internal TTA-UC quantum yield (Φ UC,g ) of 16.8% (out of a 50% maximum) for 1,4-bis((triisopropylsilyl)ethynyl)naphthalene, demonstrating the first example of a visible-to-UV TTA-UC system approaching the classical spin-statistical limit of 20%. Three other annihilators, of which 2,5-diphenylfuran has never been used for TTA-UC previously, also showed impressive performances with Φ UC,g above 12%. In addition, a new method to determine the rate constant of TTA is proposed, in which only time-resolved emission measurements are needed, circumventing the need for more challenging transient absorption measurements. The results reported herein represent an important step toward highly efficient visible-to-UV TTA-UC systems that hold great potential for driving high-energy photochemical reactions.

Water-soluble ruthenium complex-pyrene dyads with extended triplet lifetimes for efficient energy transfer applications

“…Finally, we turn to studies on photon upconversion via sensitized triplet-triplet annihilation (sTTA), which represents another photochemical application relying on tailor-made sensitizers, [83][84][85][86] in particular in aqueous solution where pronounced solubility and aggregation issues can arise. 29,87 We selected the protonated form of 9-(methylaminomethyl)anthracene (MAMA, see Fig.…”

Progress and perspectives: fluorescent to long-lived emissive multifunctional probes for intracellular sensing and imaging

“…Further, the collision between the two triplet-excited molecules leads to the promotion of a molecule to a higher energy singlet state resulting in upconversion luminescence. 202,203 Li and co-workers reported an inorganic-organic hybrid nanoprobe, TTA-Nd-NPs, for the in vivo ratiometric detection of temperature. 200 The nanoprobe consisted of a temperatureresponsive, triplet-triplet annihilation (TTA) chromophore (PtTPBP, TTA sensitizer), BDM (TTA annihilator), and the reference unit NaYF 4 :Nd (Fig.…”

“…158 The TTA process in such a probe involves the triplet state of an organic molecule as an intermediate excited state. 201,202 Generally, the probe consists of molecules known as a sensitizer and an annihilator having similar triplet energies. The sensitizer absorbs the energy and transfers its triplet energy to the annihilator resulting in a triplet excited state of the annihilator.…”

“…Further, the collision between the two triplet-excited molecules leads to the promotion of a molecule to a higher energy singlet state resulting in upconversion luminescence. 202,203…”

Enhancing photon upconversion with thermally activated sensitization and singlet energy collection

“…Typical TTA upconversion maintains a theoretical spin statistical limit towards an upconversion quantum yield of approximately 20% (out of 50% maximum). Although the TTA upconversion systems in solution have achieved a relatively high upconversion quantum efficiency, [19][20][21] the solid-state TTA upconversion system is attracting more and more attention due to its application relevance and polymeric and crystalline TTA upconversion systems have been realized via various doping approaches. [22][23][24] However, in solid systems with dense chromophores, the singlet energy back transfers from upconverted annihilators to sensitizers become prominent and must be tackled to further improve the upconversion quantum efficiency (Fig.…”