The isomeric effect on structure and photophysical property of organic fluorescent material: synthesis, structures, and photophysical properties of two novel D-π-π-A prototype fluorescent material

Two novel D-pi-pi-A prototype organic fluorescent compounds, namely (E)-2-(3-([1,1 '-biphenyl]-4-yl)-1-(naphthalen-2-yl)allylidene)malononitrile (3-BNM) and (E)-2-(1-([1,1 '-biphenyl]-4-yl)-3-(naphthalen-2-yl)allylidene)malononitrile (1-BNM) were synthesized to examine the isomeric effect on their structures and photophysical properties. The results indicated that 3-BNM and 1-BNM display different crystal packing and optical properties, because of the differences in substitution position. 3-BNM molecules packed into a 2D layer structure, while a 2D layer structure was formed in 1-BNM. Compared to that of 1-BNM, red-shifted emissions were observed in the crystal and dilute solution of 3-BNM. The structure-property relationship of the two isomers showed that it is the differences in electronic structures that lead to their different emission behaviors. The obvious isomeric effect indicated that subtle manipulation of substitution position is indeed a feasible and efficient way for tuning the structures and photophysical properties of D-pi-pi-A prototype organic fluorescent materials.