Shape-responsive adsorption of an oval macrocycle co-deposited with guest molecules

Abstract

Shape persistent macrocycles (SPMs) consist of an annular π-conjugated backbone and flexible side chains. They are considered as promising components for generating interesting self-assembly nanopatterns and act as templates to entrap guest molecules on the two-dimensional (2D) surface. Herein, we design and synthesize an oval six-membered macrocycle (M1) with benzo[1,2-b:4,3-b′]dithiophene (BDT) units connected by four acetylenyl and two butanediynyl linkers. M1 molecules were investigated by scanning tunneling microscopy (STM) to illustrate their self-assembly behaviors and interactions with guest molecules (triphenylene (Tp) and pyrene (Py)) on a graphite surface. STM result reveals that the M1 molecules could form three ordered macrocyclic patterns due to their alkyl chains’ different extended orientations on the graphite surface, which were used to entrap selectively guest molecules of Tp and Py. The outline of M1 can be changed from an oval shape to a round shape when Tp molecules are immobilized in the cavities. However, the coadsorption of Py could not change the shape of the conjugated macrocycle. The possible reason is that larger size triphenylene can deform the macrocycle's shape to coadsorb in the cavities while Py does not. Molecular mechanics (MM) simulations were also used to further reveal the host–guest nanopatterns’ formation mechanism and adsorption stability on the graphite surface.