Experimental and Calculated Spectra of π-Stacked Mild Charge-Transfer Complexes: Jet-Cooled Perylene·(Tetrachloroethene) n , n = 1,2

The S0 ↔ S1 spectra of the mild charge-transfer (CT) complexes perylene·tetrachloroethene (P·4ClE) and perylene·(tetrachloroethene)2 (P·(4ClE)2) are investigated by two-color resonant two-photon ionization (2C-R2PI) and dispersed fluorescence spectroscopy in supersonic jets. The S0 → S1 vibrationless transitions of P·4ClE and P·(4ClE)2 are shifted by δν = −451 and −858 cm–1 relative to perylene, translating to excited-state dissociation energy increases of 5.4 and 10.3 kJ/mol, respectively. The red shift is ∼30% larger than that of perylene·trans-1,2-dichloroethene; therefore, the increase in chlorination increases the excited-state stabilization and CT character of the interaction, but the electronic excitation remains largely confined to the perylene moiety. The 2C-R2PI and fluorescence spectra of P·4ClE exhibit strong progressions in the perylene intramolecular twist (1au) vibration (42 cm–1 in S0 and 55 cm–1 in S1), signaling that perylene deforms along its twist coordinate upon electronic excitation. The intermolecular stretching (Tz) and internal rotation (Rc) vibrations are weak; therefore, the P·4ClE intermolecular potential energy surface (IPES) changes little during the S0 ↔ S1 transition. The minimum-energy structures and inter- and intramolecular vibrational frequencies of P·4ClE and P·(4ClE)2 are calculated with the dispersion-corrected density functional theory (DFT) methods B97-D3, ωB97X-D, M06, and M06-2X and the spin-consistent-scaled (SCS) variant of the approximate second-order coupled-cluster method, SCS-CC2. All methods predict the global minima to be π-stacked centered coplanar structures with the long axis of tetrachloroethene rotated by τ ≈ 60° relative to the perylene long axis. The calculated binding energies are in the range of −D0 = 28–35 kJ/mol. A second minimum is predicted with τ ≈ 25°, with ∼1 kJ/mol smaller binding energy. Although both monomers are achiral, both the P·4ClE and P·(4ClE)2 complexes are chiral. The best agreement for adiabatic excitation energies and vibrational frequencies is observed for the ωB97X-D and M06-2X DFT methods.

Transfer and effects of 1,2,3,5,7-pentachloronaphthalene in an experimental food chain.

Polychlorinated naphthalenes are environmentally relevant compounds that are measured in biota at concentrations in the μg/kg lipid range. Despite their widespread occurrence, literature data on the accumulation and effects of these compounds in aquatic ecosystems are sparsely available. The goal of this study was to gain insights into the biomagnification and effects of 1,2,3,5,7-pentachloronaphthalene (PeCN52) in an experimental food chain consisting of benthic worms and juvenile rainbow trout. Worms were contaminated with PeCN52 by passive dosing from polydimethylsiloxane silicone. The contaminated worms were then used to feed the juvenile rainbow trout at 0.12, 0.25 or 0.50 μg/g fish wet weight/day, and the resulting internal whole-body concentrations of the individual fish were linked to biological responses. A possible involvement of the cellular detoxification system was explored by measuring PeCN52-induced expression of the phase I biotransformation enzyme gene cyp1a1 and the ABC transporter gene abcb1a. At the end of the 28-day study, biomagnification factors were similar for all dietary intake levels with values between 0.5 and 0.7 kg lipid(fish)/kg lipid(worm). The average uptake efficiency of 60% indicated that a high amount of PeCN52 was transferred from the worms to the fish. Internal concentrations of up to 175 mg/kg fish lipid in the highest treatment level did not result in effects on survival, behavior, or growth of the juvenile trout, but were associated with the induction of phase I metabolism which was evident from the significant up-regulation of cyp1a1 expression in the liver. In contrast, no changes were seen in abcb1a transcript levels.