Tunable Charge\nTransport Using Heterocycles-Flanked\nAlkoxyphenanthrenes for High-Performing OFETs

A series of new heterocycles-flanked alkoxyphenanthrenes\nwith D′-D-D′\nand A-D-A architecture was synthesized for high-performance solution-processable <i>p</i>-channel, <i>n</i>-channel, and ambipolar organic\nfield-effect transistors. The impact of electron-donating and -accepting\nabilities of the sulfur- and nitrogen-containing heteroaromatics on\nphotophysical, electrochemical, and semiconducting properties was\nanalyzed. The presence of heteroaryl rings improves the extended conjugation,\ntwo-dimensional lattices of π–π stacks, and increased\nmolecular interaction of the functionalized phenanthrenes (<b>PN</b>) to allow better self-assembly. The electronically dynamic <b>PN</b> self-assembles into continuous microdomains, forming percolation\nchannels for holes, electrons, or both reliant on functionalization.\nThe low-lying LUMO levels of the compounds enabled ambipolar transport\nand reduced energy levels for charge injections. Spin-coated devices\nfabricated using functionalized <b>PN</b> with sulfur-containing\nheteroaryl substituted <b>PN</b> exhibited the highest hole\nmobility of 0.85 cm<sup>2</sup>/(V s) with 10<sup>8</sup> on/off current\nratio. Compounds with A-D-A architecture showed n-channel/ambipolar\ncharge transport, especially napthalimide acceptor substituted <b>PN</b> exhibited n-channel electron mobility of 0.78 cm<sup>2</sup>/(V s) and an on/off ratio of 10<sup>6</sup>. X-ray diffraction and\nscanning electron microscopy studies further delineate the impact\nof efficient packing in the film. Quantum chemistry calculations combined\nwith Marcus–Hush electron transfer theory interpret the transport\nparameters, and heteroatoms are established to impact the charge mobility\nintensely.