Chiral Dibenzopentalene-Based Conjugated Nanohoops through Stereoselective Synthesis

Conjugated nanohoops allow to investigate the effect of radial conjugation and bending on the involved pi-systems. They can possess unexpected optoelectronic properties and their radially oriented pi-system makes them attractive for host-guest chemistry. Bending the pi-subsystems can lead to chiral hoops. Herein, we report the stereoselective synthesis of two enantiomers of chiral conjugated nanohoops by incorporating dibenzo[a,e]pentalenes (DBPs), which are generated in the last synthetic step from enantiomerically pure diketone precursors. Owing to its bent shape, this diketone unit was used as the only bent precursor and novel corner unit in the synthesis of the hoops. The [6]DBP[4]Ph-hoops contain six antiaromatic DBP units and four bridging phenylene groups. The small HOMO-LUMO gap and ambipolar electrochemical character of the DBP units is reflected in the optoelectronic properties of the hoop. Electronic circular dichroism spectra and MD simulations showed that the chiral hoop did not racemize even when heated to 110 degrees C. Due to its large diameter, it was able to accommodate two C60 molecules, as binding studies indicate.

Automated summary

Conjugated nanohoops exhibit unexpected optoelectronic properties and chirality, with bending of the pi-system leading to the synthesis of chiral hoops. By incorporating dibenzo[a,e]pentalenes and using a bent diketone unit, chiral conjugated nanohoops were stereoselectively synthesized with small HOMO-LUMO gap and ambipolar electrochemical character. The chiral hoop showed stability even at high temperatures and was capable of accommodating two C60 molecules, as indicated by binding studies.