Molecular Switching via Multiplicity-Exclusive E/Z Photoisomerization Pathways

摘要: Mutual exclusivity in the nature of forward and reserve isomerization pathways holds promise for predictably controlling responses photoswitchable materials according to molecular structure or external stimuli. Herein we have characterized E/Z photoisomerization mechanisms visible-light-triggered switch 1,2-dithienyl-1,2-dicyanoethene (4TCE) chlorobenzene with ultrafast transient absorption spectroscopy. We observe that switching occur exclusively by relaxation through electronic manifolds different spin multiplicity: trans-to-cis only occurs via within singlet manifold on a time scale 40 ps; contrast, cis-to-trans is not observed above 440 nm, but two rapid ISC processes into out triplet scales ∼2 ps 0.4 ns, respectively, when excited at higher energies (e.g., 420 nm). Observation cis-4TCE consistent photoinduced dynamics related thiophene-based oligomers. Interpretation photophysical underlying these reactions supported observation efficiently triplet-sensitized energy transfer, whereas does not. Quantum-chemical calculations reveal T1 potential surface barrierless along coordinate central ethylene dihedral angle (θ) from cis Franck-Condon region (θ = 175°) geometries are trans ground-state well; furthermore, S1 surfaces cross substantial spin-orbital coupling. In total, demonstrate photoswitching 4TCE operates multiplicity-exclusive pathways, enabling additional means tailoring performance manipulating spin-orbit couplings variations physical environment.