Journal of the American Chemical Society, Vol.120, No.7, 1474-1478, 1998
Effect of solvent polarity, pH, and metal complexation on the triple fluorescence of 4-(N-1,4,8,11-tetraazacyclotetradecyl)benzonitrile
Triple fluorescence is observed for 3-(N-1,4,8,11-tetraazacyclotetradecyl)benzonitrile (DMABN-Cyclam) in ethanol, corresponding to a locally excited (LE) singlet state, a twisted intramolecular charge-transfer (TICT) state. and an intramolecular exciplex (E). The LE state emission dominates the spectrum in nonpolar solvents such as n-hexane, while polar solvents stabilize the charge-transfer states, TICT and E. Optimal intramolecular exciplex emission, however, was observed in toluene, while the TICT band was maximal in water. The influence of pH on the fluorescent properties of DMABN-Cyclam were studied, indicating that protonation of cyclam strongly influences the equilibria existing between the three excited-state species, as well as the extent of quenching apparent for each excited-state band. DMABN-Cyclam uniquely responded to the addition of micromolar quantities of transition metal cations with varying changes in the triple fluorescence emission.