Influence of Molecular Symmetry and Terminal Substituents on the Morphology and OFET Characteristics of S,N-Heteropentacenes

Abstract

Many heteroacenes have been extensively studied to improve device performances; however, the morphological effects stemmed from the chemical modification on a multiscale remain less explored. In this research, five axisymmetric S,N-heteropentacenes (DTPT, DTPT-Ph, DTPT-CN, DTPT-PYCN, and DTPT-BTCN) are studied to reveal the influences of molecular symmetry and end-capping substituents on the structure–property relationship, the thermal stability, crystallization behavior, film morphology, and OFET performance. Phase behavior was probed by differential scanning calorimetry (DSC), while the quality of the crystal array and structural details was investigated by optical microscopy (OM) and grazing-incidence wide-angle X-ray scattering (GIWAXS). The analytic results reveal that (1) the parent axisymmetric S,N-heteropentacene, DTPT, is hard to crystallize, which hinders the preparation of high-quality crystal arrays for the OFET application. (2) The incorporation of π-conjugated electron-withdrawing (π-EW) endcaps that provide extended conjugation length and enhanced molecular polarity is required to form oriented crystal arrays to deliver reasonable OFET characteristics. (3) The π-EW endcaps with conformational freedom, such as −BTCN, due to the asymmetric feature of benzothiadiazole (BT), can hinder bulk phase crystallization and cause conformational disorder in the crystal array. Hence, the tradeoff of introducing the end-substituents to reinforce the poor crystalline nature of S,N-heteroacenes should be carefully considered.

Chemical Defects and Energetic Disorder Impact the Energy‐Level Alignment of Functionalized Hexaazatriphenylene Thin Films

“…While structural disorder of the thin film is expected to have a similar impact on the DOS broadening of both frontier molecular orbitals, conformational disorder can lead to unequal broadening. [63] Conformational disorder is mainly discussed for polymers [64][65][66] but can also impact oligomer thin films [67,68] for which the broadening of the frontier molecular orbital DOS was shown directly by a combination of STM and scanning tunneling spectroscopy, [69,70] and indirectly by the combination of energy level modeling on the DFT level and UPS. [71,72] While the planar structure of HATNA does not favor molecular distortions, the different symmetries of the HOMO and LUMO (Figure S8, Supporting Information) might lead to a different susceptibility to broadening of the HOMO and the LUMO DOS.…”

Current developments of eco-friendly organic field-effect transistors: from molecular engineering of organic semiconductors to greener device processing

“…74 Meanwhile, Wang and co-workers closely analyzed the changes in the properties of semiconducting materials according to the change in the terminal structure of the heteropentacene moiety. 103 In particular, DTPT-PYCN (structure shown in Fig. 11), which contains pyrimidine with a cyano group substituted as the terminal group, showed excellent solubility in THF, unlike other materials that dissolve in solvents harmful to the human body such as carbon disulfide, 1,2,4-trichlorobenzene, and 1-chloronaphthalene.…”

“…11), which contains pyrimidine with a cyano group substituted as the terminal group, showed excellent solubility in THF, unlike other materials that dissolve in solvents harmful to the human body such as carbon disulfide, 1,2,4-trichlorobenzene, and 1-chloronaphthalene. 103 In addition, including the PYCN end group with DTPT was found to contribute to the charge mobility by lowering the crystallinity of the material. Hence, a design concept involving the inclusion of a small-molecule substituent on the terminus of an OSC was established.…”