Journal of Photochemistry and Photobiology A: Chemistry 163 (2004) 165–170 Quantifying ground-state complexation between Ag + and polycyclic aromatic hydrocarbons in dilute aqueous solution via fluorescence quenching Ji Hoon Lee a , Mark A. Schlautman a,b,∗ , Elizabeth R. Carraway a,b,1 , Soobin Yim a , Bruce E. Herbert c a Clemson Institute of Environmental Toxicology, Clemson University, Pendleton, SC 29670, USA b School of the Environment, Clemson University, Clemson, SC 29634-0919, USA c Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843, USA Received 30 July 2003; received in revised form 11 November 2003; accepted 20 November 2003 Abstract 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 ob- served in the presence of high concentrations of Ag + , indicating that ground-state cation–aromatic  electron interactions occurred. Ag + complexation constants (K 1 and K 2 ) 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 complex- ation 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– interactions. © 2004 Elsevier B.V. All rights reserved. Keywords: Pyrene; Naphthalene; Silver ion; Metal complexation; Dynamic quenching; Exciplex; Time-resolved fluorescence; Steady-state fluorescence 1. Introduction Ever since single ring aromatic compounds were reported to form 1:1 complexes with silver ions [1–3], polycyclic aromatic hydrocarbons (PAHs) have been recognized as potential donor molecules for preparing Ag + –aromatic  complexes in aqueous [4–7] and organic solvents [5,8,9]. The Ag + –aromatic  interaction has also been studied in gas [10,11] and solid [12–18] phases. Mulliken [19] for- mulated a theoretical model for the bonding between silver perchlorate and benzene and Fukui et al. [20] provided a molecular orbital theoretical treatment of the electronic requirements of Ag + –aromatic  interactions. Based on these results [19,20], cation–aromatic  interactions are ∗ Corresponding author. Tel.: +1-864-656-4059; fax: +1-864-656-0672. E-mail addresses: mschlau@clemson.edu (M.A. Schlautman), ecarraw@clemson.edu (E.R. Carraway). 1 Co-corresponding author. Tel.: +1-864-646-2189; fax: +1864-646-2277. expected to consist of charge-quadrupole, charge-dipole, charge-induced dipole, charge transfer, dispersion force, electostatic interaction, and hydrophobic components. Re- cently, Munakata et al. [21] provided a review on the formation of Ag + ion–PAH complexes in various phases. Andrews and Keefer [4] suggested that the water soluble aromatic  complexes AgAr + and Ag 2 Ar 2+ are in equilib- rium with the aromatic compound and free Ag + , and that the monosilver complex is predominant in the ground-state. In other words, the complexation constant for Ag 2 Ar 2+ is a minor component in calculating the overall speciation. Kofahl and Lucas [5] determined Ag + complexation con- stants of various PAHs in an aqueous medium containing KNO 3 and AgNO 3 at unit ionic strength and in equimolal water–methanol solutions containing NaNO 3 and AgNO 3 at ionic strength 0.5 using a solubility enhancement method. They found that Ag + complexation constants of phenan- threne (Phen) depended significantly on the polarity of the solvent systems. For example, the complexation constant for formation of AgPhen + in aqueous medium was 3.3 1010-6030/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/S1010-6030(03)00443-X