Trans-cis photoisomerization of the stilbenes and a reexamination of the positional dependence of the heavy-atom effect

Time-resolved studies on the photoisomerization of a phenylene–silylene–vinylene type compound in its first singlet excited state

“…This behavior cannot be attributed to intersystem crossing based on the absence of triplet-state formation on direct trans-ST excitation. Moreover the relatively low quantum yield of trans-cis isomerization, F trans-cis ¼ 0.28 in hexane [6] compared to 0.40 for trans-stilbene in pentane [15,31] on irradiation at l¼313 nm, cannot explain the short lifetime of trans-ST in its S 1 state. We consider that the main deactivation route of trans-ST in its S 1 state is the repopulation of its ground state directly through internal conversion or with the intermediacy of a species twisted about one of the ethylenic bonds, in agreement with the mechanism proposed for trans-stilbene [15,31].…”

Blue-Fluorescent Antibodies

“…Hence, for 1, there is an increase in fluorescence efficiency with a concurrent decrease in the efficiency of trans + cis photoisomerization (14,15). Similarly, when substitutions are made that constrain or "stiffen" the structure of 1 from twisting as in 10, the isomerization yield is zero and the 4, approaches unity (16,17). If the confines of a specific antibody binding site imparted "stiffness" to 2, then we would expect a reduction in isomerization and an enhanced 4,.…”

Photoisomerization by Hula Twist: 2,2′‐Dimethylstilbene and a Ring‐Fused Analogue

“…Therefore, the ( E )‐ 2 to ( Z )‐ 2 photoisomerization also proceeded efficiently. The quantum yield of the reaction was found to be 0.18±0.02 10. On the basis of the relative irradiation periods, we believe that this value is a good reflection of the ease of isomerization of cis ‐diarylethylenes in low‐temperature glass.…”