Syntheses and Properties of Two Isomeric Phenanthroacephenanthrylene Derivatives

Cyclopenta-annulated polycyclic aromatic hydrocarbons (CP-PAHs) are of significant interest due to their unique optoelectronic properties and applications in organic electronic devices. Phenanthroacephenanthrylene (PAP) isomers are CP-PAHs that have been rarely investigated, and only the [9,10-e]PAP isomer was explored to date. Herein, we report the syntheses, crystal structure and optoelectronic properties of two PAP isomers, 7-ethoxy[2,1-e]PAP 1 and 9-ethoxy[1,2-e]PAP 2. The structural isomers were synthesized in multi-steps, and structural elucidations were performed using NMR, mass, and single-crystal X-ray diffraction analyses, revealing planar backbone of the isomers. UV-visible absorption and fluorescence spectra of compound 1 were red-shifted than that of 2, suggesting smaller HOMO–LUMO energy gap which is further validated by DFT calculations that suggested the lowering of HOMO–LUMO spacing could be attributed to the greater destabilization of HOMO for 1.