Controlling the Chiroptical Properties of Pyrene-Based Tweezers by Conformation Locking

Circularly polarized excimer emission is highly sought-after due to its potential in advanced optoelectronic and sensing applications. However, achieving precise control over this phenomenon remains a significant challenge. To address this challenge, we have designed a system where circularly polarized excimer emission could be controlled via conformation locking and aggregation. The structural conformations were extensively examined using circular dichroism spectroscopy, X-ray crystallography, 1H NMR spectroscopy, and molecular modelling. Self-assembly was triggered by adding water to THF solutions, with water-induced aggregation leading to redshifts in absorption bands and excimer emission in T1 (major monomer emission), T2 (minor monomer emission) and T3 at high water content. Additionally, the effects of aggregation on chiroptical properties were studied using circular dichroism and circularly polarized luminescence spectroscopy, revealing a reduction in circular dichroism signal and circularly polarized luminescence quenching with increasing water content. Notably, T3 displayed both excimer and monomer circularly polarized luminescence signals, reflecting two excited-state geometries. This research underscores the impact of rigidity on the photophysical and chiroptical properties of pyrene and opens avenues for further exploration of BINOL-pyrene-based macrocycles and cages.