Pairwise Packing of Anthracene Fluorophore: Hydrogen-Bonding-Assisted Dimer Emission in Solid State

Anthracene
derivatives possessing a carbamate group and an ester
group at their 9- and 10-positions, respectively, were prepared to
furnish pairwise packing of anthracene fluorophores in their crystal
structures. They were nonluminescent in ethanol solution and showed
AIE (aggregation-induced emission) in aqueous ethanol solution and
in solid state. Crystal structure analysis of them showed that the
H-bonding networks involved in their crystal structures could be classified
into four patterns, H-bonding between the carbamate and the ester
carbonyl (motif A), H-bonding between the carbamate and the ester
oxygen atom (motif B), H-bonded cyclic dimer of carbamate moieties
(motif C), and H-bonded chain among carbamate moieties (motif D).
Compounds with pairwisely packed anthracene fluorophores showed dimer
emission with the longer fluorescence wavelength than others without
the pair formation. Fluorescence maximum wavelengths and lifetimes
become longer proportional to the degree of overlapping of two facing
anthracene π-planes.

分别在9位与10位带有氨基甲酸酯基团（carbamate group）与酯基（ester group）的蒽（Anthracene）衍生物被合成，以实现其晶体结构中蒽荧光团的成对堆积。该类衍生物在乙醇溶液中无发光性能，在乙醇水溶液及固态下则表现出聚集诱导发光（aggregation-induced emission, AIE）特性。对该类衍生物的晶体结构分析表明，其晶体中的氢键网络可分为四类模式：氨基甲酸酯与酯羰基之间的氢键（基序A）、氨基甲酸酯与酯氧原子之间的氢键（基序B）、氨基甲酸酯基团形成的氢键结合环状二聚体（基序C），以及氨基甲酸酯基团间的氢键链（基序D）。具备成对堆积蒽荧光团的化合物，其发射的二聚体荧光波长较未形成荧光团配对的化合物更长。最大荧光波长与荧光寿命均随两个相对的蒽π平面的重叠程度增大而呈正比增长。