Intermeshed Diphenylacetylenes with Axial Rotation Restricted by Intramolecular Donor–Acceptor Interactions
Year: 2026
Type: preprint
Abstract: Diphenylacetylene (DPA) rotates almost freely around the acetylene axis with rotation mainly restricted by steric repulsion or covalent tethers. We report intermeshed diphenylacetylenes, in which bent π-conjugated units attached to DPA termini cause two donor–acceptor pairs to overlap with each other on opposite sides of the axis. Density functional theory calculations showed that a twisted, stacked conformation with a 36–40° dihedral angle was the most stable for all four molecules. The estimated P/M interconversion barriers (12.8–21.4 kcal/mol) increased with donor and acceptor strength. Upfield shifts in 1H NMR spectra and long-wavelength absorption bands assigned to intramolecular charge-transfer transitions indicated that the stacked conformation predominated in solution. Because rotation was restricted rather than fixed, the molecules exhibited dynamic axial chirality. In a derivative bearing pyridyl groups as acceptors, acid–base interaction with (+)- or (–)-camphorsulfonic acid biased the P/M equilibrium and gave mirror-image induced circular dichroism spectra.
Source: ChemRxiv
Institution: Yamagata University
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7225119389