Thiepin‐Fused Heteroacenes: Simple Synthesis, Unusual Structure, and Semiconductors with Less Anisotropic Behavior

Abstract

The simple one-pot syntheses of sulfur-rich thiepin-fused heteroacences with an alkylidene-fluorene framework, THA1 and THA6 (thiepin-fused heteroacene 1 or 6, in which the thiepin is conjugated at both ortho positions with SCH3 or SC6 H13 , respectively), is reported. Based on electrochemical studies and theoretical calculations, their LUMO energies are relatively low (-3.26 eV), and their HOMO and HOMO-1 orbitals are nearly degenerate. The thiepin ring contributes mainly to HOMO-1 and LUMO orbitals, however, HOMO orbitals dominantly reside on thienoacence rings. Within the crystal of THA1, the molecules adopt a herringbone arrangement and multiple intermolecular interactions lead to the formation of a 2D network. Interestingly, THA6 shows totally different intermolecular arrangements. Organic field-effect transistor (OFET) devices show both compounds exhibiting p-type semiconducting behavior. Thin films or microcrystals of THA1 possess relatively high hole mobility. Moreover, the mobilities of the microcrystal of THA1 along three directions are in the same order, thus the hole-carrier transporting within the hexagonal-plane of microcrystal of THA1 exhibits less anisotropic behavior. In comparison, both thin films and microrods of THA6 show low hole mobilities. This agrees well with the intermolecular arrangements and interactions within crystal of THA6. Further theoretical calculations reveal that significant intermolecular electronic coupling among HOMO-1 orbitals and sulfur atoms play an important role in intermolecular electronic coupling for THA1.

Modification of Side Chains of Conjugated Molecules and Polymers for Charge Mobility Enhancement and Sensing Functionality

“…22,23 We reported sulfur-rich thiepine-fused heteroacenes T1 and T6 (Figure 1a) with alkyl chains of different lengths. 24 Their energy levels and bandgaps are almost the same, and thus the alkyl chains exert no effect on their electronic structures. However, the intermolecular orientation and stacking within the crystals are totally different.…”

“…It is known that tight and multidimensional intermolecular stacking arrangements are beneficial for enhancing semiconducting properties of organic semiconductors . The alkyl chain effect on the intermolecular arrangements and semiconducting properties have been reported for several conjugated molecular systems. , We reported sulfur-rich thiepine-fused heteroacenes T1 and T6 (Figure a) with alkyl chains of different lengths . Their energy levels and bandgaps are almost the same, and thus the alkyl chains exert no effect on their electronic structures.…”

Two Photon Absorption Study of Low-Bandgap, Fully Conjugated Perylene Diimide-Thienoacene-Perylene Diimide Ladder-Type Molecules

“…All reagents purchased commercially were used without further purification except for toluene and tetrahydrofuran (THF), which were dried over sodium/ benzophenone. 1 H NMR and 13 C NMR spectra were recorded on a Bruker DRX-500 spectrometer with tetramethylsilane as an internal reference. High Resolution MALDI-TOF spectra were recorded on Bruker Solarix 9.4T.…”

“…In the past few decades, ladder-type materials have been continuously investigated for their potential applications in organic electronics. − Different types of structures have been developed, ranging from all hydrocarbon polyacenes to systems containing heterocyclic aromatic rings. , In the past years, different polyacenes have been reported, but their stability, solubility, and processability are major issues that prevent them from extensive exploration for applications. , Recently, we reported a novel method to synthesize conjugated heteroacenes with excellent solubility in organic solvents due to the side-chain modification. These molecules were investigated via nonlinear optical techniques and were shown to exhibit a sizable TPA cross-section. − However, these materials are rather electron-rich and can be slowly oxidized due to high HOMO energy level caused by fused thienyl units .…”

Exploration of Syntheses and Functions of Higher Ladder-type π-Conjugated Heteroacenes

“…LHAs containing S atom are among the most popular skeletons for organic semiconductors since S-S interaction can potentially facilitate intermolecular charge transport of the resulting materials. 31 S-bridged LHAs show higher oxidative stability than the all-phenyl polycyclic compounds because diminished aromaticity of the thiophene ring shows broad band gaps and lowers the highest occupied molecular orbital (HOMO) energy levels. In addition, when the 5-membered thieno ring replaces the six-membered benzene ring, the undesired Diels-Alder addition and oxygen addition across the two active CH groups are impossible in S-bridged LHA.…”