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Interactions of Ag+ with naphthalene and pyrene in aqueous solution were investigated using ultraviolet (UV) absorption and steady-state and time-resolved fluorescence spectroscopies. Small red-shifts in the two primary absorption bands of naphthalene and pyrene were observed in the presence of high concentrations of Ag+, indicating that ground-state cation–aromatic π electron interactions occurred. Ag+ complexation constants (K1 and K2) for naphthalene were determined directly from steady-state and time-resolved fluorescence data, whereas the formation of a pyrene–Ag+ exciplex required an additional correction to remove its interference on apparent pyrene complexation constants. The correction utilized ratios of the exciplex and monomer preexponential factors obtained from pyrene fluorescence decay curves measured at several emission wavelengths that were impacted to different degrees by the exciplex emission. The novel approach developed here to quantify ground-state complexes between Ag+ and polycyclic aromatic hydrocarbons (PAHs) offers new opportunities to investigate weak metal–organic complexes such as those resulting from cation–π interactions. [Copyright &y& Elsevier]

The primary mechanism responsible for the dynamic fluorescence quenching of polycyclic aromatic compounds (PACs) by Ag+ ions is enhanced intersystem crossing from the lowest singlet excited state to the lowest triplet excited state. For some PACs, however, exciplex formation with Ag+ in polar organic solvents has also been reported. Quenching of pyrene fluorescence by Ag+ in two polar solvent systems (aqueous and ethanolic solutions) was examined here using steady-state and time-resolved fluorescence techniques. In both solvents, quenching led to the formation of a pyrene–Ag+ exciplex, (1Py⋯Ag+)*, which rapidly equilibrated with excited singlet pyrene molecules (1Py*) and Ag+ ions. The exciplex and pyrene monomer emission spectra strongly overlapped, with the dominant exciplex peaks in water and ethanol red shifted from the 0–0 transition of pyrene by 5.08 and 2.56 kJ/mol, respectively. Rate constants for the formation and dissociation of the exciplex were much larger than the radiative and nonradiative decay rate constants for both the excited state monomer and exciplex. The short exciplex fluorescence lifetimes and very low quantum yields observed in the two solvents can be attributed to enhanced nonradiative decay processes for the exciplex. The emission quantum yield of the exciplex formed in aqueous solution was approximately an order of magnitude larger than that in ethanolic solution, which is likely to be attributable to the higher polarity of water versus ethanol. [Copyright &y& Elsevier]

Abstract: A new, simple, and rapid method to determine Setschenow (i.e., salting-out) constants for luminescent organic compounds in aqueous solutions has been developed using steady-state and time-resolved fluorescence measurements. Application of the new method was demonstrated using pyrene in the presence of nonquenching (K+) and dynamically quenching (Cs+) akali metal chloride salt solutions at room temperature. For these two model systems, Setschenow constants for pyrene salting-out by KCl and CsCl were determined to be 0.211 and 0.355M−1, respectively. We expect that the methodology reported in this paper can be applied equally well to interactions between a variety of salting-out agents and fluorescent biological and/or environmental molecules in aqueous solutions. [Copyright &y& Elsevier]

Abstract: Emission from two different peroxyoxalate chemiluminescence (PO-CL) reaction pathways (i.e., 1,1′-oxalyldiimidazole (ODI) and bis(2,4,6-trichlorophenyl)oxalate (TCPO) CL reactions) is significantly reduced in the presence of increasing Cu2+ concentrations. The CL intensity decrease in the ODI-CL reaction results from deactivation of the high-energy intermediate(s) by Cu2+, whereas the apparent quenching in the TCPO-CL reaction results from both this effect and formation of Cu2+–imidazole (ImH) complexes [Cu(ImH) n=1–4]2+. Because the reaction between Cu2+ and ImH occurs competitively with the formation of a high-energy intermediate (X) in TCPO-CL reactions, accurately determining Cu2+ concentrations with a TCPO-CL-based system is more difficult versus an ODI-CL-based system. Using ODI-CL, the detection limit of Cu2+ dissolved in water was determined to be 5.0×10−8 M (signal:noise=3) in a 1cm fluorescence flow micro-cell. ODI-CL-based systems are expected to be useful for the rapid quantification of many quenchers in environmental and biological samples because the interactions between the high-energy intermediate(s) and quencher are very rapid relative to other competitive reactions. [Copyright &y& Elsevier]