The Interplay of Strongly and Weakly Exchange-Coupled Triplet Pairs in Intramolecular Singlet Fission

• Published in: Journal of the American Chemical Society Vol. 146; no. 43; pp. 29664 - 29674
• Main Authors: Millington, Oliver, Montanaro, Stephanie, Sharma, Ashish, Dowland, Simon A., Winkel, Jurjen, Grüne, Jeannine, Leventis, Anastasia, Bennett, Troy, Shaikh, Jordan, Greenham, Neil, Rao, Akshay, Bronstein, Hugo
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 30-10-2024
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.4c10483

Singlet fission (SF) and triplet–triplet annihilation upconversion (TTA-UC) nominally enable the interconversion of higher-energy singlet states with two lower-energy triplet states and vice versa, with both processes having envisaged application for enhanced solar power devices. The mechanism of SF/TTA-UC involves a complex array of different multiexcitonic triplet-pair states that are coupled by the exchange interaction to varying extents. In this work a family of bounded intramolecular SF materials, based upon the chromophore 1,6-diphenyl-1,3,5-hexatriene, were designed and synthesized. Their SF behavior was characterized using fluorescence lifetime, transient absorption, and magnetic field dependence studies. The capacity for the formation of weakly exchange-coupled triplet pairs, and subsequent spin-evolution, is shown to be strongly dependent upon the combined factors of oligomer size and geometry. By contextualizing these results with the wider SF literature, we present a general schematic model for SF/TTA-UC of greater completeness than portrayed elsewhere.