Condensed aromatics—XIV. Fluoranthene

Microextraction based on microplastic followed by SERS for on-site detection of hydrophobic organic contaminants, an indicator of seawater pollution

Microplastics (MPs) have been proven to concentrate hydrophobic organic contaminants (HOCs) from seawater as the sorbent phase, and the concentration of HOCs in aqueous solutions could be estimated from MPs preloaded with HOCs by equilibrium partition coefficient. This study firstly proposed to in situ quantify fluoranthene (a representative HOCs) pre-concentrated on MPs using surface enhance raman scattering (SERS) in combination with mathematical models, as an efficient monitoring tool for fluoranthene pollution in the aquatic environment. AgNPs-coated quartz (AgNPs@SiO2) substrate was fabricated. The SERS substrate was tested using fluoranthene standard solution with the minimal detectable concentration of 1 ng/mL achieved. Applying SERS for the detection of fluoranthene sorbed on MPs, the detection limit of fluoranthene on MPs was 3.3 ng/g, where the concentration in the corresponding equilibrium seawater was 0.97 ng/mL. Since more than one fluoranthene peak was observed, the quantitative detection was investigated by interval partial least square model. Eight characteristic peak ranges were selected to develop the model for predicting fluoranthene concentration, with R²c and R²v of 0.90 and 0.82, respectively. The study provides a promising solution to monitor trace level of contaminations in aquatic environment, using MPs as the passive sampler.

Photoelectron spectroscopy of anthracene and fluoranthene radical anions

We report the slow electron velocity map imaging spectroscopy of cryogenically cooled anthracene and fluoranthene radical anions, two similarly sized polycyclic aromatic hydrocarbon molecules. The results allow us to examine the lowest energy singlet and triplet states in the neutral molecules on equal footing from the anionic ground state. The analysis of the experimental spectra is aided by harmonic calculations and Franck-Condon simulations, which generally show good agreement with experimental values and spectra. The electron affinity of fluoranthene is measured to be 0.757(2) eV, which is larger than that of anthracene at 0.532(3) eV. The lowest energy triplet state in anthracene is observed at 1.872(3) eV above the singlet ground state, while that of fluoranthene is observed at 2.321(2) eV above its singlet ground state. Comparisons of experimental and calculated spectra show that in addition to the Franck-Condon active modes, there is a clear presence of vibrational modes that gain intensity via vibronic coupling in both the singlet and triplet states in both molecules. In addition, the triplet state generally exhibits increased vibronic coupling compared to the singlet state, with the fluoranthene triplet state exhibiting evidence of distortion from C_2v symmetry.

Electronic Spectroscopy of Nonalternant Hydrocarbons Inside Helium Nanodroplets

We have recorded the electronic spectra of three polycyclic aromatic hydrocarbons (acenaphtylene, fluoranthene, and benzo(k)fluoranthene) containing a five-member ring and their van der Waals complexes with argon and oxygen with a molecular beam superfluid helium nanodroplet spectrometer. Although the molecules, which differ by addition of one or two fused benzene rings to acenaphtylene, have the same point group symmetry, the spectral lineshapes show distinct differences in the number of zero phonon lines and shapes of the phonon wings. Whereas the smallest molecule (acenaphtylene) has the most complicated line shape, the largest molecule (benzo(k)fluoranthene) shows different lineshapes for different vibronic transitions. The van der Waals complexes of fluoranthene exhibit more peaks than the theoretically allowed number of isomeric complexes with argon/oxygen. The current models of molecular solvation in liquid helium do not adequately explain these discrepancies.