Molecular Engineering of Chromophores to Enable Triplet–Triplet Annihilation Upconversion

Abstract

Triplet−triplet annihilation upconversion (TTA-UC) is an unconventional photophysical process that yields high-energy photons from low-energy incident light and offers pathways for innovation across many technologies, including solar energy harvesting, photochemistry, and optogenetics. Within aromatic organic chromophores, TTA-UC is achieved through several consecutive energy conversion events that ultimately fuse two triplet excitons into a singlet exciton. In chromophores where the singlet exciton is roughly isoergic with two triplet excitons, the limiting step is the triplet−triplet annihilation pathway, where the kinetics and yield depend sensitively on the energies of the lowest singlet and triplet excited states. Herein we report up to 40-fold improvements in upconversion quantum yields using molecular engineering to selectively tailor the relative energies of the lowest singlet and triplet excited states, enhancing the yield of triplet−triplet annihilation and promoting radiative decay of the resulting singlet exciton. Using this general and effective strategy, we obtain upconversion yields with red emission that are among the highest reported, with remarkable chemical stability under ambient conditions.

Bidirectional triplet exciton transfer between silicon nanocrystals and perylene

“…This value is comparable to that recently reported for an upconversion system employing t Bu 4 perylene as the triplet fusion emitter and palladium( ii ) meso -tetraphenyl-tetrabenzoporphyrin (PdTPTBP) as the light absorber, which displayed upconversion efficiencies ranging from 0.1–7.6% depending on the relative concentration of t Bu 4 perylene to PdTPTBP. 35 …”

“…This performance is comparable to that recently demonstrated using the same perylene annihilator coupled with a Pd-porphyrin light absorber. 35 Our work demonstrates that the introduction of short, chemical linkers between molecules and Si can enable triplet exciton exchange between these materials for the design of new systems for both photon upconversion and light harvesting.…”

“…This value is comparable to that recently reported for an upconversion system employing tBu 4perylene as the triplet fusion emitter and palladium(II) mesotetraphenyl-tetrabenzoporphyrin (PdTPTBP) as the light absorber, which displayed upconversion efficiencies ranging from 0.1-7.6% depending on the relative concentration of tBu 4 perylene to PdTPTBP. 35 Bolstered by these results, we attempted to push the performance of our upconversion system further into the farred by using a 730 nm laser source to excite Si:3EP. We indeed obtain blue emission upon 730 nm excitation, but over the excitation power range examined, this upconverted emission displayed a dependence on the incident power that lies between a linear and quadratic dependence (slope ¼ 1.27, Fig.…”

Photon Upconversion Hydrogels for 3D Optogenetics

“…There are only a limited number of NIR‐absorbing sensitizers, [ 33 ] but platinum(II) tetraphenyltetranaphthoporphyrin (PtTPTNP; Figure 1 and Figure S3, Supporting Information) can be paired with both TTBP [ 18 ] and TIPS‐An, [ 33 ] exhibiting an apparent anti‐Stokes shift of ≈1.0 eV. While both annihilators work well, we chose to focus on TIPS‐An because it often outperforms TTBP in terms of upconversion efficiency, [ 33,34 ] and it can be more readily prepared on a large scale.…”

Red Light Optogenetics in Neuroscience

“…Therefore, UPNC can help to circumvent the penetration problem. Upconversion systems can be based on upconverting rare earth metals or on triplet–triplet annihilation upconversion from organic chromophores ( Zhu et al, 2019 ; Fallon et al, 2020 ). Both systems are constantly being further developed.…”