Interpretation of the Emission Fluorescence Spectra of Two Fluoroionophores: DMABN-Crown4 and DMABN-Crown5

We discuss an interpretation of the emission signal of a class of dimethylaminobenzonitrile (DMABN) derivatives, based on a stochastic model approach. This study is prompted by the interest in building relatively simple theoretical tools for understanding the static and dynamic properties of metal chelation-controlled fluorescent molecular systems with internal flexibility and solvation effects, which can be used as fluorescent sensors of metal ions. We proceed by extending a stochastic modeling approach, previously used for DMABN, in which internal degrees of freedom are coupled to an effective solvent relaxation variable. The model is based on an integrated approach that combines stochastic methods and QM calculations. The static and dynamic properties of the molecule are obtained by a combination of a continuum treatment and a detailed solute dynamics. Simple computational approximations lead to a semianalytical treatment of the resulting equations, which reproduce correctly the static spectra at room temperature of 4-(1-aza-4,7,10-trioxacyclododecyl) benzonitrile (DMABN-Crown4) and 4-(1-aza-4,7,10,13-tetraoxacyclododecyl) benzonitrile (DMABN-Crown5) in solvents with different polarity. A qualitative analysis of the dynamic spectra of the DMABN-Crown4 is also presented. A discussion is finally provided on how combined quantum and classical methods can be used to define a general robust and reliable computational approach for predicting fluorescence properties of organic molecules in solution. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 110: 368-375, 2010