Unveiling the Full Configurational Landscape of Chiral Phenanthrene-Bridged Diarylethene

Abstract

We report the first complete experimental resolution of the configurational landscape of a phenanthrene-bridged diarylethene (DAE) with unsymmetrical substitution. Four stereoisomers-two antiparallel and two parallel-were isolated and fully characterized by chiral HPLC, circular dichroism, NMR, and single-crystal X-ray diffraction. This study demonstrates that parallel conformers, previously assumed to exist as a single meso form, are in fact distinct enantiomeric pairs. Thermal and kinetic analyses show that antiparallel conformers are both energetically favored and longer-lived, with racemization half-lives of up to one week at room temperature. The photochromic behavior of the phenanthrene-bridged DAE has been investigated in solution and in different condensed phases. In a PMMA matrix, and in the crystalline state, the closed antiparallel form displays significantly enhanced thermal stability at room temperature. These results uncover a previously unexplored stereochemical dimension in DAE chemistry, providing new avenues for the rational design of intrinsically chiral photochromic switches.