Influence of Intermolecular Packing on Light Emitting Efficiency and Carrier‐Mobility of Organic Semiconductors: Theoretical Descriptor for Molecular Design

Integration of luminescence and carrier transport is of prime interest for optoelectronics, but full with challenges in organic semiconductors. Previously, it has been demonstrated that intermolecular charge transfer (ICT) in the herringbone H-aggregate can lend oscillator strength to the lowest-lying dark state if electron transfer (t(e)) and hole transfer (t(h)) integrals are in phase (same sign) and greater than 2J$\sqrt 2 J$, where J is exciton coupling. In this work, both herringbone and pi-pi stackings are considered and a universal descriptor I =2teth/[(|te|+|th|)center dot|J|]$I\;{\bf = }2{t_{\rm{e}}}{t_{\rm{h}}}/\left[ {(|{t_{\rm{e}}}|{\bf + }|{t_{\rm{h}}}|)\cdot|J|} \right]$ is proposed. It is found that for pi-pi stacking with I > 1 and for herringbone with I>2$I{\bf > }\sqrt 2 $, respectively, the lowest dark state could become bright through mixing ICT component. Accordingly, it is found that eclipsed packing and use of molecules with acene-like frontier molecular orbital profiles favor larger I value than the other packing patterns. Finally, with the help of the proposed descriptor, 13 high-mobility emissive unit cores from 32 fused ring molecules are effectively screened out.