Data from: Fluorescence and photophysical properties of xylene isomers in water: with experimental and theoretical approaches

A thorough analysis of the photophysical properties involved in electronic
transitions in excitation–emission spectra of xylene isomers has been
carried out using the time-dependent density functional theory
(PBEPBE/6-31 + G(d,p)) method. For the first time a structural and
spectroscopic investigation to distinguish isomers of xylene, a widespread
priority pollutant, was conducted experimentally and theoretically. The
fluorescence properties of xylene isomers (sole and mixture (binary and
ternary)) in water were studied. The fluorescence peak intensities of
xylenes were linearly correlated to concentration, in the order of
p-xylene > o-xylene > m-xylene at an excitation/emission
wavelength (ex/em) of 260 nm/285 nm for o-, m-xylene and ex/em
265 nm/290 nm for p-xylene at the same concentration. The theoretical
excitation/emission wavelengths were at ex/em 247 nm/267 nm, 248 nm/269 nm
and 251 nm/307 nm for o-, m- and p-xylene, respectively. The vertical
excitation and emission state energies of p-xylene (ex/em 4.94 eV/4.03 eV)
were lower and the internal conversion energy difference (0.90 eV) was
higher than those of m-xylene (ex/em 5.00 eV/4.60 eV) (0.4 eV) and
o-xylene (ex/em 5.02 eV/4.64 eV) (0.377 eV). The order of theoretical
emission and oscillator strength (0.0187 > 0.0175 > 0.0339)
for p-xylene > o-xylene > m-xylene was observed to be in
agreement with the experimental fluorescence intensities. These findings
provide a novel fast method to distinguish isomers based on their
photophysical properties.