Three-in-One π-Conjugated Chiral Macrocycles: Photoswitching, Amplified Chirality, and Photo-Tailored Chiroptics

Chiral macrocycles have attracted considerable attention because of their fascinating circular chiral topologies, circularly distributed electronic structures, and excellent chiroptical features. However, the challenging synthesis and limited cases hinder the understanding, improvement, and regulation of their optoelectronic properties. To avoid this dilemma, we employed cyclic Suzuki-Miyaura coupling between dithienylethene (DTE) and [6]helicene to firstly synthesize donor-acceptor (D-A)-type π-conjugated chiral macrocycles, including m-[1 + 1], m-[2 + 2], and m-[3 + 3], where these compounds displayed photocontrollable ring sizes and chiroptical properties. More importantly, continuous amplification in chirality can be achieved via distinctive multiple chiral-centers-bonding in series within helical rings, giving high |g_abs| and |g_lum| of up to 0.023 and 0.013, respectively. The macrocycles were endowed with a photoswitchable function that is absent in previously documented π-conjugated chiral macrocycles. Both the cavity sizes and chiroptical properties could be photoregulated. As typical examples, the cavity dimension of m-[3 + 3]-PPP was photoadjusted from 25.8 × 19.8 to 22.6 × 18.3 Å, accompanied by reversible photoswitched |g_abs| between 0.023 and 0.014 and remarkable CPL ON/OFF behavior. Moreover, a size-photoswitching correlation was revealed innovatively, i.e., the photoswitching ability increased with increasing ring size. Our study provides a new guidance for developing high-performance chiral systems and novel stimuli-responsive chiral macrocycles and provides ideal platforms for understanding chiral structure-functionality relationships.