Constructing a pyrene-based dimer in a crystal by adjusting the steric hindrance over the pyrene plane

The structure-property relationship is always the focus when organic light-emitting materials are used mainly in the aggregated state in some fields, such as optoelectronic devices, sensors, and bioimaging. To clarify a clear structure-property relationship between the aggregate structure and the luminescent property, the intermolecular dimer, which represents the smallest aggregate in a number, is selected as an ideal research model. However, how to achieve an intermolecular dimer by a rational molecular design is rarely found in previous papers in this field. Here, we design and synthesize three pyrene derivatives, aiming at achieving the pyrene-based dimer in a solid state, by bridging pyrene and benzo[d]thiazole (BZT) in a different position on a phenylene. The pyrene and BZT groups are connected with each other in the ortho-, meta-, and para-positions of the phenylene to construct three molecules Py-oBZT, Py-mBZT, and Py-pBZT. Experimental and theoretical investigations demonstrate that only Py-oBZT shows pyrene-based dimer stacking with a discrete feature due to the large steric hindrance provided by the BZT group. Compared to individual pyrenes in the crystal, the pyrene-based dimer in the Py-oBZT crystal exhibits a different molecular orientation, which is verified by the presence of multiple potential wells of the pyrene dimer using a theoretical simulation of the potential energy surface. This work not only examines the effect of steric hindrance on the formation of the pyrene dimer packing, but also provides an understanding of the multiplicity of the pyrene dimer structures. The presence of an ortho-linked substituent in pyrene can lead to steric hindrance on one side of the pyrene plane, which prevents the formation of undesired interactions and promotes the selective formation of dimers in a desired orientation.

Automated summary

In this study, the formation of pyrene-based dimers in a solid state was achieved by designing and synthesizing three pyrene derivatives. The effect of steric hindrance on the formation of the dimer packing was examined, and the multiplicity of pyrene dimer structures was elucidated.