Insights into the Control of Optoelectronic Properties in Mixed‐Stacking Charge‐Transfer Complexes

Abstract

Although cocrystallization has provided a promising platform to develop new organic optoelectronic materials, it is still a big challenge to purposely design and achieve specific optoelectronic properties. Herein, a series of mixed‐stacking cocrystals (TMFA, TMCA, and TMTQ) were designed and synthesized, and the regulatory effects of the acceptors on the co‐assembly behavior, charge‐transfer nature, energy‐level structures, and optoelectronic characteristics were systematically investigated. The results demonstrate that it is feasible to achieve effective charge‐transport tuning and photoresponse switching by carefully regulating the intermolecular charge transfer and energy orbitals. The inherent mechanisms underlying the change in these optoelectronic behaviors were analyzed in depth and elucidated to provide clear guidelines for future development of new optoelectronic materials. In addition, due to the excellent photoresponsive characteristics of TMCA, TMCA‐based phototransistors were investigated with varying light wavelength and optical power, and TMCA shows the best performance among all reported cocrystals under UV illumination.

Rational Control of Charge Transfer Excitons Toward High‐Contrast Reversible Mechanoresponsive Luminescent Switching

“…Thep redicted molecular stacking mode in solid state [40] shows that NDI and Cor. molecules are alternated stacking along [100] axis with the dominated crystal planes of (001), (010) and (100), affording ab lock-like structure (Figure 2f; Supporting Information, Figure S4b).…”

Recent Progress in Polycyclic Aromatic Hydrocarbon‐Based Organic Co‐Crystals

“… [19] In DFT calculation, the frontier molecular orbitals (MOs) of D and A molecules are hybridized with an energy‐level splitting and the degree of charge transfer shows an increasing trend as the strength of acceptors augmented (Figure 4). [19] …”

“… UV/Vis/NIR absorption spectra of a) TMFA, b) TMCA, and c) TMTQ as well as their corresponding constituting single components in the solid state. Spatially enlarged FTIR spectra of powders for d, e) TMIQ, chloranil, and the TMCA co‐crystal, and f,g) TMIQ, fluoranil, and the TMFA co‐crystal [19] . Reproduced by permission of John Wiley and Sons, Copyright 2020.…”

“… MO energy‐level diagram of a) TMFA, b) TMCA, and c) TMTQ co‐crystals and the corresponding single components. Schematic diagram of the simplified simulated orbital energy levels for d) hole charge transport and e) electron charge transport along the mixed stacking direction for co‐crystals TMFA, TMCA, and TMTQ [19] . Reproduced by permission of John Wiley and Sons, Copyright 2020.…”

“…The mechanism of solution‐processing crystallization is that the co‐crystals can be obtained by the usage of the different solubility between the starting components and the co‐crystals at different solvents and/or temperatures. The evaporation of solvents is the most intensively explored technology to prepare PAH‐based co‐crystals [14d,19,24] . After all the host and guest components are dissolved completely, the co‐crystals can be formed through the multiple intermolecular interactions among the different components during slow evaporation of their solution or slow cooling of their hot solution.…”