Temperature dependence of phenanthrene cavity radius in apolar solvents and in water

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Phenanthrene, a three ring aromatic hydrocarbon, is used as a model substance for study of intermolecular interactions in dilute solutions of organic solvents and water by spectroscopic method. Temperature dependencies of shift of the S₂₀ spectrum of phenanthrene dissolved in apolar solvents and in liquid water are studied in this work. The spectroscopic data are used for analysis of the cavity radius R for phenanthrene molecule in solvents. It is shown that the value of R increases with temperature in organic solvents. In contrast, for water solution, the value of R initially grows with temperature increase (in the interval of 273.3-296 K), but becomes constant at higher temperatures. The changes of water structure in the neighbourhood of a phenanthrene molecule and probable hypothesis about causes of R value constancy in high-temperature region are discussed. Conclusion about strengthening of the water structure in an aqueous cage with phenanthrene molecule inside is done.