Position of Biphenyl Group Turning The Structure and Photophysical Property of D-π-π-A Prototype Fluorescent Material

Three novel D-π-π-A prototype compounds, namely, (E)-2-(3-([1,1'-biphenyl]-2-yl)-1-(9H-fluoren-2-yl) allylidene) malononitri-le (2-BAM), (E)-2-(3-([1,1'-biphenyl]-3-yl)-1-(9H-fluoren-2-yl)allylidene) malononitri-le (3-BAM), (E)-2-(3-([1,1'-biphenyl]-4-yl)-1-(9H-fluoren-2-yl)allylidene) malononitri-le (4-BAM) were synthesized. Furthermore, the structures and photophysical properties of three compounds were compared. Molecules of 2-BAM were packed into a 1D column structure with H-aggregation. However, both of 3-BAM and 4-BAM were packed into 3D layer structures with J-aggregation, respectively. Although three compounds all showed highly twisted molecular geometries, their molecular packing and intermolecular interactions were different. Because of the differences in electronic structures of molecules, the three compounds displayed different emission behaviors in solid and dilute solution. This study indicated that changing the position of biphenyl groups is an effective way to turn the structures and photophysical properties of such D-π-π-A prototype fluorescent material.