Reversible Photoisomerization of Monolayers of π‐Expanded Oligothiophene Macrocycles at Solid–Liquid Interfaces

Self‐assembled monolayers of a π‐expanded oligothiophene macrocycle undergo photoisomerization between their Z,Z and E,E diastereomers at the interface between octanoic acid solutions and highly oriented pyrolytic graphite (HOPG). The switching process proceeds in situ at the solid–liquid interface and was followed by scanning tunneling microscopy (STM). Upon illumination with light at 365 nm (546 nm), a monolayer of Z,Z‐8mer (E,E‐8mer) photoisomerizes to the E,E‐8mer (Z,Z‐8mer) form with changes in 2D hexagonal packing. These findings provide insight towards the design of photoresponsive surfaces with desirable optoelectronic and structural (host–guest) properties.