Enhancing the Statistical Probability Factor in Triplet Fusion Upconversion via TIPS Functionalization.

Abstract

We investigated the effect of triisopropylsilyl (TIPS) functionalization of annihilators in triplet-triplet annihilation photon upconversion on their spin statistical probability factor. A new green annihilator 3,9-bis((triisopropylsilyl)ethynyl)perylene (TIPS-PY) displaying record red-to-green TTA-UC quantum yield of 13.7% (50% theoretical maximum) is synthesized. This remarkable efficiency was achieved due to the following features of the TIPS functionalization of PY: 1) high fluorescence quantum yield of 95%, 2) reduced triplet energy to 1.29 eV enabling efficient triplet energy transfer (~100%) from the sensitizer, PdTPBP (T1= 1.5 eV), and 3) a high efficiency of singlet generation after triplet coupling, indicated by the statistical probability factor, f = 39.2% ± 2.4%. Notably, the f value of TIPS-PY surpasses other annihilators in the 470-540 nm emission range by ≥1.5-fold. DFT and TDDFT calculations revealed that TIPS-functionalized chromophores (TIPS-PY, TIPS-naphthalene, and TIPS-anthracene), exhibit singlet-like character in their triplet dimer state which can enhance the coupling of the triplet-pair state with the excited singlet-state, thereby increasing the efficiency of singlet generation a phenomenon undisclosed before. Furthermore, the suitable T1 of TIPS-PY enables upconversion of 730 nm light when sensitized with Os(m-peptpy)2(TFSI)2 (T1 = 1.63 eV), demonstrating the broad upconversion range of TIPS-PY in the phototherapeutic window desired for biological applications

L. N. acknowledges the Erasmus + Traineeship Program, P. B. and M. M. acknowledge financial support from the La-Caixa junior research leadership-post doctoral program (ID: 100010434, fellowship code: LCF/BQ/P122/11910023) the State Investigation Agency, through the Severo Ochoa Programme for Centres of Excellence in R&D (CEX2023-001263-S) and project PID2021-123873NB-I00 for financial support. L. N. and A. B. P. acknowledge the start-up funds provided by the University of California San Diego and the use of facilities and instrumentation supported by NSF through the UC San Diego Materials Research Science and Engineering Center (UCSD MRSEC), grant # DMR-2011924. K. M. P. acknowledges funding from the European Research Council (No. 101002131), the Swedish Energy Agency, the Göran Gustafsson Foundation, the Swedish Research Council, Swedish Research Council Formas, the European Research Council (ERC) under grant agreement CoG, PHOTHERM – 101002131, the Catalan Institute of Advanced Studies (ICREA), and the European Union's Horizon 2020 Framework Programme under grant agreement no. 951801. M. D., G. K., K. K., acknowledge the “Universities” Excellence Initiative” programme by the Ministry of Education, Science and Sports of the Republic of Lithuania under the agreement with the Research Council of Lithuania (project No. S-A-UEI-23-6). M. S. is grateful for financial support from the Agencia Española de Investigación (MCIN/AEI/10.13039/501100011033) for projects RED2024-154178-T and PID2023-147424NB-I00 and from the Generalitat de Catalunya for Project 2021SGR623 and ICREA Academia 2025 prize to M. S. N. Y. ackno