Host–guest interaction-induced emission enhancement of amphiphilic AIEgens: a computational study

Abstract

To achieve the efficient and precise regulation of aggregation-induced emission in supramolecular systems, revealing the role of host–guest interactions in AIEgens is of vital importance. Using the theoretical protocol that combines molecular dynamics simulations and the hybrid quantum mechanics/molecular mechanics calculations, we explored the mechanism of host–guest interaction-induced emission enhancement of amphiphilic guest molecules (AIEgens) as both dispersed monomers and assembled aggregates. We confirmed that the binding pattern of host–guest inclusions between α-cyclodextrin (CD) and three amphiphilic guest molecules is that the interior hydrophobic cavity of CD hosts one phenyl ring of the TPE moiety and part of PEG chain of the guest; simultaneously, the exterior hydrophilic surfaces of CD fasten the PEG chain and adjacent phenyl rings of the TPE moiety of guest molecules by intermolecular hydrogen bonds and O–H⋯π interactions, respectively. The packing density of the assembled aggregates decreases as the CD concentration increases. The analysis of the radiative decay rate constants and the reorganization energy indicate that the monomer emission is enhanced after host–guest complexation; meanwhile, combining host–guest interactions and aggregation effects could further increase the fluorescence efficiency, because both host–guest interactions and the aggregation effect can effectively retard the low-frequency intramolecular phenyl ring rotational motions and CC double bond plane twisting, thus suppressing the nonradiative decay channels. The fluorescence emission spectra are also blue-shifted after complexation. Our theoretical protocol is general and applicable to other AIEgens in the supramolecular field, thus laying a solid foundation for the rational design of advanced AIE materials.