Exploring Cyclopentannulation as an Effective Synthetic Tool to Design Polycyclic Aromatic Hydrocarbon AIEgens for Bioimaging

Synthesis of various polycyclic aromatic hydrocarbons (PAHs) from a palladium-catalyzed [3 + 2] cyclocondensation reaction is reported herein. The design strategy consisted of reacting the sterically hindered 1,2-bis(3,5-di<i>tert</i>-butylphenyl)acetylene <b>2</b> with myriad brominated anthracene and pyrene surrogates, resulting in the formation of target molecules <b>MCP1-2</b> and <b>DCP1-3</b>, which exhibited excellent solubility in commonly used organic solvents and unveiled prominent aggregation-induced emission (AIE) characteristics in tetrahydrofuran and water solvent mixtures. Calculations using density functional theory (DFT) were utilized to validate both the contorted structures of the target molecules and their electronic conjugation featuring HOMO-LUMO band gaps (Δ<i>E</i>) in the range of ∼2.88 to 2.97 eV for the monocylopentannulated PAHs <b>MCP1-2</b>, and between ∼2.23 to 2.41 eV for the dicyclopentannulated PAHs <b>DCP1-3</b>. Furthermore, the biomedical features of <b>DCP2</b> were investigated in cell-imaging experiments employing the RAW 264.7 macrophage cell line as a model system showing a high biocompatibility for <b>DCP2</b>, thus paving the way for its potential application in bioimaging. These findings underscore the significance of the target compounds as prominent AIEgens with exceptional photophysical properties and biocompatibility, therefore promoting them as valuable tools for bioimaging applications.