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

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 photo-luminescence quantum yields (PLQY) of approximately 40% in toluene. In addition, the absolute powder PLQYs of C-0-, C-2-, C-3-, C-4-, and C-6-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 C-1-, C-3-, and C-4-Ph-Ants show hole mobilities of up to 2.40, 1.34, and 1.00 cm(2) V-1 s(-1), respectively, with mobilities of 3.40, 1.57, and 0.82 cm(2) V-1 s(-1), for C-0-, C-2-, and C-6-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.

Automated summary

The derivatives of anthracene show strong emission and charge carrier mobility within a molecule, with the alkyl chain length playing a crucial role in crystal structures, thermal properties, and photophysical characteristics. Adjusting the alkyl chain length can significantly impact the charge mobilities, with shorter chains generally leading to higher mobilities due to enhanced film order and intermolecular charge transport properties.