Donor-Acceptor Conjugated Macrocycles with Polyradical Character and Global Aromaticity

Polyradical character and global aromaticity are fundamental concepts that govern the rational design of cyclic conjugated macromolecules for optoelectronic applications. Here, we report donor-acceptor (D-A) conjugated macromolecules with and without pi-spacer derivatives to tune the antiferromagnetic couplings between the unpaired electrons. The macromolecules without pi-spacer have a closed-shell electronic configuration and show global nonaromatic character in the singlet and lowest triplet states. However, the derivatives with pi-spacer develop a nearly pure open-shell diradical and a very high polyradical character, not reported for D-A type macromolecules. Furthermore, the pi-spacer derivatives display global nonaromaticity in the singlet ground state, but global aromaticity in the lowest triplet state, according to Baird's rule. The absorption spectra of the open-shell macromolecules calculated with time-dependent density functional theory indicate intensive light absorption in the near-infrared region and broadening to 2,500 nm, making these materials suitable for numerous optoelectronic applications.