Synthesis of Optically Active π-Stacked Molecules: Effect of π-Stacking Position on the Chiroptical Properties

Abstract

Abstract Optically active V-shaped and X-shaped molecules consisting of stacked five-ringed para-phenylene-ethynylenes (PPEs) were prepared using planar chiral [2.2]paracyclophanes as chiral building blocks. Despite having the same absolute configurations, the V- and X-shaped molecules exhibited opposite circular dichroism (CD) and circularly polarized luminescence (CPL) signals. For example, the (Sp)-isomer of the V-shaped molecule and (Sp)-isomers of the X-shaped molecules exhibited negative and positive CPL emissions, respectively. Simulations using time-dependent density-functional theory calculations indicated that the lowest unoccupied molecular orbital (LUMO) of the V-shaped molecule in the S1 state was localized in one of the stacking PPEs, whereas the LUMOs of the two X-shaped molecules in the S1 state were delocalized in both PPEs via the [2.2]paracyclophane moieties. The theoretical results were reproduced and explained the CD and CPL behaviors well.