Reaction amplification with a gain: Triplet exciton-mediated quantum chain using mixed crystals with a tailor-made triplet sensitizer

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 121; no. 14; p. e2401982121
• Main Authors: Paul, Indrajit, Konieczny, Krzysztof A, Chavez, Roberto, Garcia-Garibay, Miguel A
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 02.04.2024
• Subjects: Acetophenone; Adiabatic; Adiabatic flow; Amplification; Atomic energy levels; Benzene; Cations; Crystals; Energy transfer; Ethyl benzene; Ethylbenzene; Excitons; Isomerization; Mixed crystals; Photochemical reactions; Photochemicals; Photochemistry; Solid solutions; Triplet state; mixed crystals; solid-state reaction; exciton-enabled; quantum chain reaction; triplet excited state
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2401982121

Photochemical valence bond isomerization of a crystalline Dewar benzene ( ) diacid monoanion salt with an acetophenone-linked piperazinium cation that serves as an intramolecular triplet energy sensitizer ( ) exhibits a quantum chain reaction with as many as 450 product molecules per photon absorbed (Φ ≈ 450). By contrast, isomorphous crystals of the diacid monosalt of an ethylbenzene-linked piperazinium ( ) lacking a triplet sensitizer showed a less impressive quantum yield of ca. Φ ≈ 22. To establish the critical importance of a triplet excited state carrier in the adiabatic photochemical reaction we prepared mixed crystals with as a dilute triplet sensitizer guest in crystals of . As expected from their high structural similarities, solid solutions were easily formed with the triplet sensitizer salt in the range of 0.1 to 10%. Experiments carried out under conditions where light is absorbed by the triplet sensitizer-linked can be used to initiate a triplet state adiabatic reaction from to , which can serve as a chain carrier and transfer energy to an unreacted where exciton delocalization in the crystalline solid solution can help carry out an efficient energy transfer and enable a quantum chain employing the photoproduct as a triplet chain carrier. Excitation of mixed crystals with as little as 0.1% triplet sensitizer resulted in an extraordinarily high quantum yield Φ ≈ 517.