Modelling Ultralong Phosphorescence in Molecular Crystals

Organic Phosphorescence (UOP) has generated significant interest because of its applications in several areas such as photovoltaic cells, bioimaging and anticounterfeiting. The molecule of carbazole (Cz) is commonly used as a building block in organic materials for optoelectronic applications, acting as a light-absorbing, electron donor and emitting moiety. Cz and its derivatives display UOP at room temperature. While the processes behind UOP have been associated with the stabilisation of H-aggregates, recent experimental studies indicate the presence of impurities drives the mechanism keeping the excited states alive for long times.1 In this talk, I will discuss the mechanism behind light-induced processes in crystalline and impure Cz and some derivatives using embedding methods developed in our group.[2,3] I will revisit the role of aggregation and isomeric impurities on the excited state pathways and analyse the mechanisms for exciton, Dexter energy transfer and electron transport considering Marcus and Marcus–Levich–Jortner theories.[4,5] Our excited state mechanisms provide a plausible interpretation of the experimental results and support the formation of charge-separated states at the defect/host interface. We believe these results contribute to a better understanding of the factors that enhance the excited-state lifetimes in organic materials and the role of doping with organic molecules.
[1] Chen, C.; Chi, Z.; Chong, K. C. ; Batsanov, A. S.; Yang, Z.; Mao, Z.; Yang, Z.; Liu, B. Nat. Mater., 2021, 20, 175–180.
[2] Rivera, M.; Dommett, M.; Sidat, A.; Rahim, W.; Crespo‐Otero, R. J. Comput. Chem., 2020, 41, 1045–1058.
[3] Rivera, M.; Dommett, M.; Crespo‐Otero, R. J. Chem. Theory Comput., 2019, 15, 2504–2516.
[4] Hernández, F. H.; Crespo-Otero, R. J. Mater. Chem. C, 2021, 9, 11882–11892.
[5] Sidat, A.; Hernández, F. J.; Stojanović, L.; Misquitta, A. and Crespo-Otero, R. Phys. Chem. Chem. Phys. 2022, 24, 29437