Herein,we compared the optical properties of four compounds with an o-carborane cage linked to 1H-phenanthro[9,10-d]imidazole at the ortho-(oPC),meta-(mPC),or para-position(pPC)of the 2-phenyl ring or at the C2-positi...Herein,we compared the optical properties of four compounds with an o-carborane cage linked to 1H-phenanthro[9,10-d]imidazole at the ortho-(oPC),meta-(mPC),or para-position(pPC)of the 2-phenyl ring or at the C2-position(PC)of the phenanthroimidazole moiety.In the solid state,pPC and PC exhibited intense intramolecular charge transfer(ICT)-based emission centred at∼560 nm,while oPC and mPC exhibited dual emission in high-energy(λ_(em)≈385 nm)and low-energy(λ_(em)≈580 nm)regions due to a locally excited transition and ICT-based emission,respectively.Thus,the quantum efficiency and radiative decay constant of ICT-based emission in the film state were much higher for pPC and PC than for oPC and mPC.Analysis of solid-state molecular structure revealed a notable geometric difference between these two pairs,showing that the C-C bond axis of the o-carborane was orthogonal to the plane of the appended aromatic group for pPC and PC but not for oPC and mPC.Theoretical modelling of the low-energy transition in the first excited states of pPC and PC upon the rotation of the o-carborane cage verified that the above orthogonality plays an important role in the maximisation of ICT-based luminescence.Our findings suggest that the molecular geometry around the o-carborane cage is a major factor determining the efficiency of ICT-based radiative decay in o-carboranyl-substitutedπ-conjugated fluorophores.展开更多
基金supported by the National Research Foundation of Korea(NRF)grant(NRF-2020R1A2C1006400 and NRF-2021M3H4A1A02055684 for K.M.Lee)funded by the Ministry of Science and ICT.
文摘Herein,we compared the optical properties of four compounds with an o-carborane cage linked to 1H-phenanthro[9,10-d]imidazole at the ortho-(oPC),meta-(mPC),or para-position(pPC)of the 2-phenyl ring or at the C2-position(PC)of the phenanthroimidazole moiety.In the solid state,pPC and PC exhibited intense intramolecular charge transfer(ICT)-based emission centred at∼560 nm,while oPC and mPC exhibited dual emission in high-energy(λ_(em)≈385 nm)and low-energy(λ_(em)≈580 nm)regions due to a locally excited transition and ICT-based emission,respectively.Thus,the quantum efficiency and radiative decay constant of ICT-based emission in the film state were much higher for pPC and PC than for oPC and mPC.Analysis of solid-state molecular structure revealed a notable geometric difference between these two pairs,showing that the C-C bond axis of the o-carborane was orthogonal to the plane of the appended aromatic group for pPC and PC but not for oPC and mPC.Theoretical modelling of the low-energy transition in the first excited states of pPC and PC upon the rotation of the o-carborane cage verified that the above orthogonality plays an important role in the maximisation of ICT-based luminescence.Our findings suggest that the molecular geometry around the o-carborane cage is a major factor determining the efficiency of ICT-based radiative decay in o-carboranyl-substitutedπ-conjugated fluorophores.
