Two-photon excitation of dioxane: time-resolved measurements of excited state complex formation with water

We observed emission from the non-aromatic hydrocarbon 1,4-dioxane upon illumination with ps pulses at 380 nm. The emission intensity depended quadratically on incident power at 380 nm, indicating a two-photon process. In the absence of water the intensity decay was close to a single exponential, but displayed some evidence of an excited state process. In the presence of 1% water the emission spectra shifted dramatically to long wavelength. Water also resulted in wavelength-dependent intensity decays with negative pre-exponential factors on the long wavelength side of the emission, demonstrating the presence of an excited state reaction. At this water concentration the results are consistent with a two-state model due to emission from dioxane and a dioxane and a dioxane-water complex.