Structure, property and mechanism study of fluorenone-based AIE dyes

Aggregation-induced emission (AIE) has attracted considerable interest in recent years. An understanding of the underlying mechanisms for the AIE phenomena is also of great importance. Here, we synthesized four fluorenone derivatives, which all show typical AIE properties. Their enhanced solid-state luminescence showed a 160 nm red-shift (from 380 to 540 nm) in comparison to their luminescence in dilute tetrahydrofuran (THF) solutions. The single-crystal structure and photophysical properties revealed that the bathochromic luminescence is due to the formation of static excimers. To further demonstrate the AIE mechanism of static excimers, rather than restricted intramolecular rotation (RIR), we designed a diphenylfluorenone-diboronic acid adduct, which can react with D-glucose to create structurally rigid oligomers, resulting in the restriction of intramolecular rotations. The spectral change in the D-glucose titration of the adduct indicated that the bathochromic AIE of these fluorenone compounds cannot possibly be caused by RIR and conformational planarization. (C) 2016 Elsevier Ltd. All rights reserved.