SPECTROCHEMICAL INVESTIGATIONS OF PREFERENTIAL SOLVATION .3. EXTENSION OF THE KHOSSRAVI-CONNORS-SKWIERCZYNSKI 2-STEP COMPETITIVE SOLVATION MODEL TO FLUORESCENCE EMISSION BEHAVIOR OF POLYCYCLIC AROMATIC HYDROCARBON SOLVENT POLARITY PROBES DISSOLVED IN BINARY SOLVENT MIXTURES

The Khossravi-Connors-Skwiernynski step-wise competitive exchange mode l, which has previously led to successful descriptive expressions for solvent effects on solubility, surface tension and molecular complex f ormation, is modified to model fluorescence emission behavior of polyc yclic aromatic hydrocarbon solutes dissolved in binary solvent mixture s. Expressions are derived for calculating numerical values of the var ious step-wise exchange equilibrium constants from measured emission i ntensity ratios in mixed solvents and from measured absolute emission intensities in both pure solvents. Computation procedure is illustrate d using measured fluorescence properties of pyrene, benzo[e]pyrene, be nzo[ghi] perylene, coronene, methylcoronene and 1, 2-dimethylcoronene in n-heptane + 1, 4-dioxane and n-heptane + tetrahydrofuran mixtures. Also discussed are similarities and differences between the newly-deri ved expressions and ones based upon a recently published spectrfluorom etric probe method, and the special conditions under which both models become mathematically equivalent.