Electron Density-Dependent Mallory Photocyclization Constructs Rigid Saddle-Shaped Polycyclic Aromatic Hydrocarbons
Beibei Xiao1, Hongbo Li2, Mengjie An1
1Key Laboratory of Cluster Science, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Ministry of Education of China, Beijing, 102488, P. R. China.
Abstract:
This study reports the synthesis of three saddle-shaped polycyclic aromatic hydrocarbons (PAHs)-bFT-C, bFP-C, and bFP2-C-via Mallory photocyclization of bisfluorenylidene-dihydroacene precursors. The reaction achieved high yields (77-88%) under UV irradiation, with structural characterization confirming enhanced aromaticity and rigid frameworks in the cyclized products. Kinetic studies revealed that anthracene-containing bFP2 exhibited the fastest reaction rate, which we attribute to its elevated electron density. Photophysical studies showed strong solution fluorescence (PLQY: 45-48%) but aggregation-caused quenching (ACQ) in solids due to enhanced π-π stacking. Electrochemical analyses revealed reversible redox processes, while low-temperature spectroscopy identified deep-red phosphorescence (lifetimes: 72.6-270.0 ms). This work demonstrates how precursor architecture governs reaction kinetics and photophysical properties, providing a design strategy for nonplanar PAHs with tailored luminescence characteristics.
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