title: CCVJ is not a simple rotor probe.
abstract: The photochemistry of the rotor probe 9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ) was studied to elucidate a curious effect of fluid flow previously reported. The apparent sensitivity to fluid motion observed in CCVJ but not in the closely related molecule 9-(dicyanovinyl)julolidine (DCVJ) is found to be an indirect effect of a photoisomerization reaction. The results presented here demonstrate that it is this isomerization, rather than the commonly assumed TICT process, that confers viscosity-sensing ability on these fluorophores. In micromolar solutions in hydroxylic solvents CCVJ exists primarily in the carboxylate form. Only the E isomer of this anion is initially present in solutions prepared from the solid, but in room light such solutions rapidly achieve a photostationary state in which the E isomer and an essentially nonfluorescent Z isomer exist in comparable concentrations. The Z isomer is metastable in S(0) such that in the absence of light the solution reverts slowly to pure E. Unlike DCVJ where only a single isomer is possible, the production of long-lived photoproducts in CCVJ and other asymmetrically substituted styryenyl probes complicates their fluorescence response. Considerable care is needed when such fluorphores are used as steady-state sensors of environmental fluidity are used.
authors.affiliation: Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Rumble
authors.forename: Kacie
authors.initials: K
authors.lastname: Rich
authors.forename: Gang
authors.initials: G
authors.lastname: He
authors.forename: Mark
authors.initials: M
authors.lastname: Maroncelli
mesh_terms: D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D009570:Nitriles / Q000138:chemical synthesis / Q000737:chemistry*; D011807:Quinolizines / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D009570:Nitriles; D011807:Quinolizines; C082390:9-(2-carboxy-2-cyanovinyl)julolidine