Non‐Equal Ratio Cocrystal Engineering to Improve Charge Transport Characteristics of Organic Semiconductors: A Case Study on Indolo[2,3‐a]carbazole

Abstract

Rare studies of cocrystal engineering have focused on improving carrier mobility of organic semiconductors mainly because of the generation of ambipolarity, the alteration of the charge carrier polarity or the reduction of electronic couplings. Herein, we utilize indolo[2,3-a]carbazole (IC) as the model compound and 2,6-diphenylanthraquinone (DPAO) and 9-fluorenone (FO) as the coformers to construct IC2-DPAO and IC-FO cocrystals with 2 : 1 or 1 : 1 ratios, respectively, through hydrogen bonds and donor-acceptor interactions. Interestingly, the more appropriate packing structure, possessing not only enhanced electronic couplings but also increased intermolecular distances, is achieved in IC2-DPAO, which shows an improved carrier mobility of 0.11 cm 2 V À 1 s À 1 by four orders of magnitude relative to the IC crystal. These results suggest that non-equal ratio cocrystal engineering opens up the possibility to develop organic semiconductors with enhanced charge transport behaviors.

Transistor Properties of Charge-Transfer Complexes─Combined Requirements from Energy Levels and Orbital Symmetry

“…The observed properties are sometimes susceptible to fabrication and measurement conditions. Nevertheless, applications of the above two criteria to calculations estimated from the crystal structures provide us a good starting point to roughly predict the phenomena in many cases. − Among the “inherently ambipolar” complexes, the actual characteristics and particularly the electron/hole balance considerably depend on the electrode materials and lead to apparently monopolar behavior in some cases …”

Indolocarbazole as a Platform for Concatenated Crystalline Rotors

“…These compounds exhibit exciting optical properties and can be distinguished from each other based on the relative position of the carbazole and indole components . In the field of crystal engineering, MacGillivary, Perepichka, and Hu reported novel crystalline materials using a specific isomer, indolo­[2,3- a ]­carbazole. This isomer has two NH groups that point in the same direction, making it an excellent hydrogen-bond donor.…”