New intramolecular fluorescence probes that monitor photoinduced radical and cationic cross-linking

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'-trimeth oxy)phenylethenyl)-2,3,5,6-tetrafluorobenzene (2) show solvatochromic behav ior yielding slopes in the Lippert-Mataga equation of -13300 and -13700 cm( -1), respectively. 1 sensitively probes progress in both photoinduced radic al and cationic cross-linking. Both 1 and 2 show minor tendencies for trans -cis photoisomerization. Substituted stilbenes such as trans-2-(2',5'-dimet hoxyphenyl)ethenyl-2,3,4,5,6,-pentafluorobenzene (1r) and trans-2-(3',4',5' -trimethoxyphenyl)ethenyl-2,3,4,5,6-pentafluorobenze (2r) are less solvatoc hromic in fluorescence but evidence enhanced tendency toward photoisomeriza tion.