Energy Transfer Dynamics in Triplet–Triplet Annihilation Upconversion Using a Bichromophoric Heavy-Atom-Free Sensitizer

Abstract

A heavy-atom-free triplet sensitizer suitable for triplet-triplet annihilation-based photon upconversion was developed from the thermally activated delayed fluorescence (TADF) molecule 4CzPN by covalently tethering a pyrene derivative (DBP) as a triplet acceptor. The triplet exciton produced by 4CzPN is captured by the intramolecular pyrenyl acceptor and subsequently transferred via intermolecular triplet-triplet energy transfer (TTET) to freely diffusing pyrenyl acceptors in toluene. Transient absorption and time-resolved photoluminescence spectroscopy were employed to examine the dynamics of both the intra- and intermolecular TTET processes, and the results indicate that the intramolecular energy transfer from 4CzPN to DBP is swift, quantitative, and nearly irreversible. The reverse intersystem crossing is suppressed while intersystem crossing remains efficient, achieving high triplet yield and long triplet lifetime simultaneously. The ultralong excited state lifetime characteristic of the DBP triplet was shown to be crucial for enhancing the intermolecular TTET efficiency and the subsequent triplet-triplet annihilation photochemistry. It was also demonstrated that with the long triplet lifetime of the tethered DBP, TTET was enabled under low free acceptor concentrations and/or with sluggish molecular diffusion in polymer matrixes.

Sequentially amplified circularly polarized ultraviolet luminescence for enantioselective photopolymerization

“…Figure 3c showed the dependence of the TTA-UC quantum efficiency Φ UC on the excitation power intensity for the mixed solution of R-TP/4CzIPN, a saturation quantum yield of about 7.9% was obtained by using Coumarin 6 in DMF as a standard when the maximum efficiency is standardized to be 100% (Supplementary Methods) 60 . This value is relatively large compared with previous reports 45,48,50 . The TTA-UC mechanism could also be confirmed by the lifetime measurement.…”

“…Undoubtedly, visible-to-UV upconversion is particularly important because many applications of upconversion deal with the presence of high energy. However, few examples of visible-to-UV TTA-UC can be found in the literatures and their upconversion efficiency is unsatisfactory because of the unsuitable energy levels between sensitizers and annihilators 45 , 48 – 51 . More importantly, the UC-CPUVL with high g lum value, to the best of our knowledge, remains unexploited.…”

“…Photon upconversion affords the possibility to convert low energy photons into high energy photons. The TTA-UC has an expansion to a wider range of scientific fields in terms of applications, such as photovoltaics [37][38][39] , biomolecular systems 40 , and photocatalysis 41,42 primarily due to its high efficiency, low-power excitation [37][38][39][40][41][42][43][44][45][46][47] . Undoubtedly, visible-to-UV upconversion is particularly important because many applications of upconversion deal with the presence of high energy.…”

Discovery of Key TIPS‐Naphthalene for Efficient Visible‐to‐UV Photon Upconversion under Sunlight and Room Light**

“…Highly efficient TTA‐UC from visible/near‐infrared to visible light has been achieved through the great efforts of many groups [1–19] . On the other hand, the TTA‐UC efficiency ( η UC ) from visible light (vis, λ >400 nm) to ultraviolet light (UV, λ <400 nm) at solar irradiance has been low [20–30] . The vis‐to‐UV TTA‐UC is very important for photocatalysis and purification of the indoor environment, so it is strongly expected to improve its efficiency.…”

TIPS-Naphthalene for Efficient Visible-to-UV Photon Upconversion under Sunlight and Room Light

“…While the conversion of visible light (vis, > 400 nm) to ultraviolet light (UV, < 400 nm) is crucial for artificial photosynthesis and photocatalytic environmental cleanup, the efficiency of vis-to-UV TTA-UC (UC) at solar irradiance has been limited. [20][21][22][23][24][25][26][27][28][29][30] Relatively high vis-to-UV UC values of 5.2% and 10.2% have been observed by using semiconductor nanocrystals as donor and 2,5-diphenyloxazole (PPO) as acceptor. 31,32 However, their threshold excitation intensities (Ith), at which half of the maximum UC is obtained, were much higher (ca.…”