Size and Geometry Impact the Chiroptical Properties of Double Nanohoops

Conjugated nanohoops have attracted much attention in recent years due to their unique optoelectronic properties. A more complex geometry, in which two nanohoops are covalently linked to form a so-called double nanohoop, can have a significant influence on the morphology, (chir)optical properties and supramolecular interactions compared to a single nanohoop. Herein, we present the systematic design, synthesis, structural and chiroptical analysis of a novel series of three chiral double nanohoops together with their single hoop reference compounds. They each incorporate a tetrahydroindeno[2,1-a]indene-5,10-diol unit as an asymmetric bridge with central chirality. Notably, they display high photoluminescence quantum yields of 79-95%, along with distinct trends in absorption, emission, and energy transfer dynamics. Enantiomers of the double and reference single nanohoops were successfully separated by HPLC using a chiral stationary phase, and their chiroptical properties were investigated through electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) spectroscopy revealing increased asymmetry factors (g_abs) compared to their reference compounds. Our study provides a systematic exploration of how size, geometry, and asymmetry impact the optoelectronic behavior of chiral double nanohoops and offers valuable insight for the development of high-performance chiroptical materials.