Axially Chiral Nonalternant Polycyclic Aromatic Hydrocarbon With Consecutive Pentagons Exhibiting Large Spin-Polarized Current.

Chiral polycyclic aromatic hydrocarbons (PAH) have attracted considerable attention due to their intriguing optical and electrochemical properties. Despite substantial progress in helical PAHs, axially chiral PAHs have received comparatively little attention. Herein, we report the design and synthesis of two novel nonalternant PAHs (1 and 2) featuring two and four consecutive pentagons, respectively. Under acidic conditions, these monomers 1 and 2 undergo dimerization to afford axially chiral dimers AC1 and AC2. Single-crystal x-ray analysis reveals that the central azulene unit in 2 and AC2 displays an unusually short transannular bond (1.366 Å), leading to distinct aromaticity. Notably, dimers AC1 and AC2 exhibit reversible redox behaviors, in contrast to their monomers. In addition, the enantiomers R- and S-AC2b were separated and exhibited mirror-image circular dichroism (CD) spectra extending to 700 nm with a maximum dissymmetry factor of 1.0 × 10-3 at 535 nm. Remarkably, magnetic conductive-probe atomic force microscope measurements reveal that AC2b films support spin-polarized currents up to 300 nA at 1 V with spin polarization (SP) values of 68.7% and -51.4% for the two enantiomers, representing the first observation of chiral-induced spin selectivity (CISS) in axially chiral nonalternant PAHs. These features highlight its potential as a promising candidate for highly spin-conductive elements.