Thienyl-ethene chromophores have had great success as pericyclic photoswitches by structurally inhibiting the possibility for E/Z photoisomerization. We present the photoresponsive behaviors of a thienyl-ethene chromophore, represented by the base structure 1,2-di(bisthienyl), 1,2-dicyanoethene (4TCE), which in contrast operates exclusively through E/Z photoisomerization following excitation with visible light.  This switch differs from pericyclizing switches according to alpha vs. beta linkage, respectively, between thiophene and ethene groups. Time-resolved spectroscopic measurements reveal signatures of unusual multiplicity-specific isomerization pathways in 4TCE:  whereas trans-to-cis isomerization occurs within the singlet manifold, cis-to-trans isomerization occurs via triplets following a singlet-to-triplet conversion on a sub-ps timescale. We present recent work focused on elucidating possible mechanisms underlying the ultrafast singlet-to-triplet conversion, such as ultrafast intersystem crossing or intramolecular singlet fission. Not only does this switch design offer an alternative to azobenzenes for E/Z photoswitching, it also presents the possibility of harnessing new photophysical pathways to drive photoresponses in materials.

Photochemical pathways for motion in E/Z photoswitchable thienyl-ethenes

253rd National Meeting (2017)

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