In this article, interfacial π–π interactions of polystyrene (PS) chains next to aromatic-modified substrates were investigated. The results show that the glass transition temperature (T g) and the modulus of the supported thin PS films increased gradually from phenyltrimethoxysilane-, naphthalenetrimethoxysilyl- to 9-anthracenyltrimethoxysilane-modified substrates with the increasing number of π electrons. For the p-tolyltrimethoxysilane (p-tolyl)-modified substrates, a very weak interfacial effect was observed. As revealed by sum frequency generation (SFG), the phenyl rings in the deuterated PS (dPS) side chains were perpendicular to the interface, which was induced by the anchored aromatic groups on the surface via the parallel-displaced configuration of the π–π interactions. Enhanced interfacial interactions with an increasing number of π electrons on the surface were revealed in which the peak area of the redshifted wavenumber of the ν2 C–D stretching vibration in dPS caused by π–π interactions increased. The SFG spectra of dPS at the p-tolyl-modified substrate interface were similar to those of the octadecyltrimethoxysilane-modified substrate. It suggests that spatial hindrance due to the methyl group at the para position of the phenyl groups prevents the phenyl groups in PS from forming π–π interactions with the p-tolyl group on the substrate surface. A facile method is proposed in our work to regulate the strength of interfacial interactions, which may also be applied to other polymers with aromatic groups.

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