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

Abstract

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.

On the impact of a phosphoryl group in the recognition capabilities of 2-aminopyridines toward carboxylic acids

“…The introduction of a methyl group at position 4 leads to a decrease in the oscillator strengths, whereas, on the other hand, the presence of methyl groups in positions 3, 5 and 6 results in a net enhancement of the predicted oscillator strengths. These results, being in good agreement with experimental findings (see the ESI section 4 for more details), follow the already reported trends with the 2AP analogs, 29,42,43 suggesting that the presence of the phosphoryl group does not significantly modify the way in which the methyl substitution of the aromatic ring affects the observed trend in the spectroscopic properties of the methyl substituted 2PAP derivatives.…”

“…Such deviation has already been previously described employing other computational methods in analogous systems. 29,43…”

Unprecedented Enzymatic Synthesis of Perfectly Structured Alternating Copolymers via “Green” Reaction Cocatalyzed by Laccase and Lipase Compartmentalized within Supramolecular Complexes

“…The significant differences in quantum yield of the m -xylylenediamine and p -xylylenediamine polymers can be explained by the intrinsic fluorescent differences of the xylylenediamine monomers with the para isomer displaying fluorescence approximately 15 times greater than the meta isomer (Figures S17 and S18). The difference in monomer fluorescent intensity is further amplified by the increased rigidity (thus increased fluorescence), of the p -xylylenediamine repeating unit when incorporated into the polymer chain. The molecular mass of the copolymers has insignificant influence on the fluorescence intensity.…”

Dark matter-electron scattering from aromatic organic targets

“…and where B ψ is a prefactor defined in terms of the coefficients c ψ i for each of the six HMO's Ψ i , the expressions for which are given in Appendix A 1 [44,45].…”