Probing the Hidden Photoisomerization of a Symmetric Phosphaalkene Switch

In this study, we present the synthesis and analysis of a novel, air-stable, and solvent-resistant phosphaalkene switch. Using this symmetric switch, we have demonstrated degenerate photoisomerization experimentally for the first time. With a combination of photochemical-exchange NMR spectroscopy, ultrafast transient absorption spectroscopy, and quantum chemical calculations, we elucidate the isomerization mechanism of this symmetric phosphaalkene, comparing it to two other known molecules belonging to this class. Our findings highlight the critical role of the isolobal analogy between C=P and C=C bonds in governing nanoscale molecular motion and break new ground for our understanding of light-induced molecular processes in symmetric heteroalkene systems.