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Modulating radiative efficiency in ortho-carboranyl luminophores through electron-donating substituents: insights
Soyeon Kim1, Dong Kyun You1, Namkyun Kim1
1Department of Chemistry, Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon, Gangwon 24341, Republic of Korea. kangmunlee@kangwon.ac.kr.
Abstract:
In this study, we introduce six ortho-carboranyl compounds derived from 9,9-dimethyl-9H-fluorene 1CH-6CP, each possessing substituents with varying electron-donating capabilities. Their geometric features were comprehensively characterised through single X-ray crystallography. In rigid states (solutions at 77 K, films, aggregates, and crystals), these compounds exhibited intense intramolecular charge-transfer (ICT)-based emissions in the bluish-green spectrum. Notably, the emission quantum efficiency and radiative constant in the crystalline state were proportional to their electronic features, particularly the molecular dipole moment. Furthermore, theoretical modeling of the ground (S0) and first excited (S1) state-optimised structures indicated a gradual enhancement in the orbital occupation at each lowest unoccupied molecular orbital (LUMO) level, correlating with an increase in dipole moment. These findings strongly suggest that the ICT-based radiative efficiency in π-conjugated o-carborane is significantly influenced by the electron-donating properties of the substituents attached to the o-carborane.
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