Effect of Alkyl Chain Length on Charge Transport Property of Anthracene-Based Organic Semiconductors

Abstract

Anthracene, a simple planar building block for organic semiconductors, shows strong intermolecular interactions and exhibits strong blue fluorescence. Thus, its derivatives have a great potential to integrate considerable charge carrier mobility and strong emission within a molecule. Here, we systematically studied the influence of alkyl chain length on the crystal structures, thermal properties, photophysical characteristics, electrochemical behaviors, and mobilities for a series of 2,6-di­(4-alkyl-phenyl)­anthracenes (C n -Ph-Ants, where n represents the alkyl chain length). Among them, C n -Ph-Ants (n = 0, 1, 2, and 3) display similar layered herringbone (LHB) packing motifs, which facilitate two-dimensional charge transport and thereby enables high-performance organic field-effect transistors (OFETs). All C n -Ph-Ants exhibit similar work functions and show strong blue fluorescence with photoluminescence quantum yields (PLQY) of approximately 40% in toluene. In addition, the absolute powder PLQYs of C0-, C2-, C3-, C4-, and C6-Ph-Ants are 24.6, 8.2, 5.7, 10.9, and 8.6%, respectively. Note that the alkyl chain length shows a significant effect on the charge mobilities of C n -Ph-Ants. Our newly synthesized C1-, C3-, and C4-Ph-Ants show hole mobilities of up to 2.40, 1.34, and 1.00 cm2 V–1 s–1, respectively, with mobilities of 3.40, 1.57, and 0.82 cm2 V–1 s–1 for C0-, C2-, and C6-Ph-Ants, indicating an increasing tendency of mobility with shorter alkyl chain length. This feature is related to the microstructures of the thin films, which reveal the enhanced film order, crystallinity, and grain size with a decrease in the alkyl chain length. Moreover, we theoretically analyze the intermolecular transfer integrals of HOMOs, which increase at T-shaped contacts as the alkyl chain length decreases, which improves the intermolecular charge transport properties, leading to the increases in mobility. Interestingly, the anisotropy of the transfer integral tends to decrease upon substitution with longer alkyl chains, suggesting that alkyl chain adjustments may facilitate isotropic charge transport property in 2,6-alkylated anthracenes.

Insight into the effect of alkyl chain length and substituent bulkiness on the mobility anisotropy of benzothieno[3,2-b][1]benzothiophenes

“…Moreover, it has been found that the balance of the intermolecular transfer integrals is gradually improved by increasing the alkyl chain length of the alkylated phenyl groups in 2,6-Ants. 38 Therefore, we further speculate that the introduction of alkylated phenyl or thiophene groups may beneficial for realizing low-anisotropy of mobility in BTBTs. The reason takes into consideration (1) the alkylated phenyl or thiophene groups are used to extend the molecular π conjugation and tune molecular packing, (2) the variations of the alkyl chain length may gradually adjust the R -value to balance the intermolecular charge transport properties.…”

Recent Advances and Prospects of Small Molecular Organic Thermoelectric Materials

“…Besides the study of side chain polarity, the impact of different alkyl chain lengths on the properties of charge transport had also been investigated. [ 114 ] The results indicated that the mobility has an increasing tendency with shorter alkyl chain length, related to the ordered microstructures of the thin films and crystallinity of the materials.…”

Polarization‐ and Angle‐Dependent Plasmonic Synchronous Fluorescence Spectroscopy to Probe Molecular Vibrational Couplings on an Aluminum Nano‐Film

“…[ 18 ] Some PAHs derivatives have been widely studied in solar cells, light‐emitting diodes, organic photovoltaics, organic transistors, etc. [ 19 ] Since PAHs usually consist of multiple vibrational energy levels in short‐wavelength spectral region, [ 20 ] the investigation of PAHs‐on‐Al devices may pave the way to understand the influence of Al materials on molecular vibrational couplings, which would contribute to the further construction of efficient light‐emitting devices.…”