A geometric key for enhancing the radiative efficiency of ortho-carboranyl luminophores: Indolocarbazole- and m-terphenyl-ortho-carboranes

In this study, we introduce two ortho-carboranyl compounds, namely ICzCB and mTPCB, which exhibit different planarity in their appended π-conjugated aromatic groups, to investigate the influence of geometric effects on the regulation of the radiative efficiency. Both the compounds are fully characterized, revealing distinct geometric differences (planarity) in their single-crystal structures. While ICzCB presents strong ICT-based emission in the solid (film) state, mTPCB displays dual emission in the high- and low-energy regions that originates from locally excited (LE)- and ICT-based processes, respectively. Quantitative analysis of the photophysical characteristics of the compounds shows that the ICT-based radiative efficiency in ICzCB is higher than that in mTPCB. Consequently, these findings demonstrate that the planarity of the π-conjugated aryl group appended on o-carborane, which is represented by planar ICzCB and distorted mTPCB, is an important key to control the ICT-based radiative decay efficiency.