Aggregation-induced bathochromic fluorescent enhancement for fluorenone dyes

• Two 2,7-diphenylfluorenone derivatives have been designed and synthesized.
• They exhibited aggregation-induced emission (AIE) with high quantum yields.
• Their powder showed a 160 nm red-shifted emission compared to that recorded for their THF solution.
• The crystal structures revealed the red-shifted emission originated from the dimers.
• The AIE mechanism was further verified by a diphenylfluorenone-diboronic acid adduct.

Organic solid-state luminescence materials with aggregation-induced emission enhancement have attracted considerable interest in recent years. In this work, we develop a class of 2,7-diphenylfluorenone derivatives that exhibit prominent aggregation-induced emission properties with high solid-state quantum yields. Their solid-state powders show a ∼160 nm bathochromically shifted fluorescence and longer lifetime compared to their emission in dilute THF solution. The X-ray single structures and photophysical properties reveal that the mechanism of aggregation-induced emission in this class of fluorenone compounds is due to the formation of static excimers through hydrogen bonds in the solid state. The emission of their THF solution peaked at 380 nm and originates from the single molecule and the emission of their solid-state powder peaked at 550 nm originates from the excimers. The aggregation-induced emission properties and luminescence mechanism are further verified by the design of 2,7-diphenylfluorenone-diboronic acid adduct, which exhibited weak luminescence in high pH buffer and red-shifted strong luminescence in acidic buffer.

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