Synthesis, Self-Assembly, Aggregation-Induced Emission, and Antimicrobial Activity of Amphiphilic Tetraphenylethene (TPE) Derivatives

Tetraphenylethene (TPE)-based compounds are widely recognized for their aggregation-induced emission (AIE) behaviour, making them suitable for use in areas such as bioimaging, chemical sensing, and antimicrobial applications. In this work, we designed and synthesized two new amphiphilic compounds TPE-3M and TPE-6M, in which the hydrophilic morpholine head group is attached to a hydrophobic TPE moiety by three and six carbon chain spacers respectively. The structures of the synthesized amphiphilic molecules were characterized using various spectroscopic and microscopic techniques The AIE properties of these molecules were analysed in DMSO/H₂O system. Photophysical studies indicated that both TPE-3M and TPE-6M exhibited AIE properties, as their fluorescence enhanced when these molecules get aggregated under increasing water percentage in organic system. Additionally, antimicrobial activity of TPE-3 M and TPE-6 M were evaluated against Gram-positive and Gram-negative bacterial strains using broth-based growth inhibition assays, supported by minimum inhibitory concentration (MIC) determination and agar diffusion studies. The compound TPE-6M demonstrated concentration-dependent antibacterial activity against Gram-positive bacteria, whereas compound TPE-3M revealed moderate antimicrobial properties. These results, hence demonstrate potential application of TPE-3 M and TPE-6M for designing antimicrobial coatings. Finally, we studied the shapes and energy levels of TPE-3 M and TPE-6M in both air (gas) and a liquid (DMSO) using Density functional theory (DFT) calculation. The results of DFT studies suggest light absorbed by TPE-3 M and TPE-6 M remains in localized excited state due to lack of electronic coupling induced by carbon chain spacers lying between TPE and morpholine moiety causing restricted intermolecular rotation and subsequent AIE characteristics. Hence, the comprehensive studies presented in the manuscript, provides insights into the electronic structure–function relationship in π-conjugated systems and highlights the effect of flexible linkers on localized versus delocalized excitation behaviour.