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

Research output: Contribution to journalArticleScientificpeer-review


Original languageEnglish
Pages (from-to)318−324
JournalJournal of Physical Chemistry Letters
Issue number1
Early online date2019
Publication statusPublished - 2020
Publication typeA1 Journal article-refereed


Expanding the anti-Stokes shift for triplet–triplet annihilation upconversion (TTA-UC) systems with high quantum yields without compromising power density thresholds (Ith) 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-to-annihilator 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 Ith, a previously unattained achievement.

Publication forum classification

Field of science, Statistics Finland