New Intramolecular Fluorescence Probes That Monitor Photoinduced Radical and Cationic Cross-Linking

The fluorescence probes trans,trans- 1,4-bis[2-(2‘,5‘-dimethoxy)phenylethenyl)-2,3,5,6-tetrafluorobenzene ( 1 ) and trans,trans- 1,4-bis[2-(3‘,4‘,5‘-trimethoxy)phenylethenyl)-2,3,5,6-tetrafluorobenzene ( 2 ) show solvatochromic behavior yielding slopes in the Lippert−Mataga equation of −13 300 and −13 700 cm -1, respectively. 1 sensitively probes progress in both photoinduced radical and cationic cross-linking. Both 1 and 2 show minor tendencies for trans − cis photoisomerization. Substituted stilbenes such as trans -2-(2‘,5‘-dimethoxyphenyl)ethenyl-2,3,4,5,6-pentafluorobenzene ( 1r ) and trans -2-(3‘,4‘,5‘-trimethoxyphenyl)ethenyl-2,3,4,5,6-pentafluorobenzene ( 2r ) are less solvatochromic in fluorescence but evidence enhanced tendency toward photoisomerization.