Two-dimensional fluorescence correlation spectroscopy. I. Analysis of polynuclear aromatic hydrocarbons in cyclohexane solutions

Generalized two-dimensional (2D) correlation spectroscopy was applied to the analysis of fluorescence spectra of anthracene-phenanthrene (AN-PH) and anthracene-pyrene (AN-PY) mixtures in cyclohexane solutions. These aromatic hydrocarbons are commonly used fluorescence probes. They have fine-structured and well-characterized spectra suitable for investigating basic features of the 2D fluorescence correlation spectroscopy. The AN-PH pair was examined as an example in which the component spectra are not heavily overlapped, while the AN-PY pair is an example in which the component spectra an heavily overlapped. We used two types of perturbation to induce the intensity variations of fluorescence spectra: one is concentration change, and the other is excitation-wavelength change. Both perturbations gave a series of systematically varying spectra, which led to the development of clear synchronous and asynchronous maps. By using the 2D correlation maps thus obtained, the vibronic bands in the complicated fluorescence spectra of the mixture of the probes were successfully analyzed. This study demonstrates the usefulness and potentiality of the 2D correlation technique in the field of fluorescence spectroscopy.