Applications of chemometric methods to spectroscopic studies of aggregate formation and twisted intramolecular charge transfer in the gas phase and in non-polar solvents

Principal component analysis—self-modelling and non-linear least-squares spectral resolution methods were applied to quantitative fluorescence studies of the aggregate formation and the twisted intramolecular charge transfer (TICT) state emission of p-(N,N-diethylamino)ethylbenzoate (DEAEB) in the gas phase and in low-density supercritical ethane. A broad Gaussian-like fluorescence band at approximately 400 nm was obtained and assigned to the emission of DEAEB microcrystals or microsolids. It is shown that the red-shifted band can essentially be eliminated by keeping the sample undisturbed for a period of time and by selecting appropriate excitation wavelengths. The results support the conclusion that even in the gas phase the contribution of DEAEB TICT state emission is still significant. It is also demonstrated that a quantitative characterization of the excited state equilibium between the locality excited and TICT states of DEAEB in non-polar solvents can be accomplished by application of a spectral resolution method.