Journal of Physical Organic Chemistry最新文献

The development of biomimetic electron transfer catalysts based on proton-coupled electron transfer (PCET), which is characterized by quinone–hydroquinone π-conjugation, represents a promising approach for achieving highly efficient artificial energy conversion. Herein, I report a density functional theory (DFT)-based analysis of the electronic inductive (I) and resonance (R) effects of substituents on concerted two-proton-coupled electron transfer (2PCET) between benzene-1,2-diol (catechol) derivatives and the superoxide radical anion (O₂^•−). In this study, I investigated the relationship between the type and number of substituents and their effects on 2PCET using 12 catechol derivatives. Four types of substituents—methyl (+I, +R), chloro (−I, +R), methoxy (−I, +R), and cyano (−I, −R)—were selected in mono-, di-, tri-, and tetra-substituted forms to isolate and analyze their electronic effects without additional functionalities. My DFT results confirmed that substituent effects selectively enhance either proton or electron transfer along a sequential PCET pathway. Further analysis revealed that the R effect is the primary driving force for concerted 2PCET, where an increasing number of methyl or chloro substituents promotes the reaction, whereas cyano substituents suppress it. The I and R effects influence the electronic properties of the catechol molecule in proportion to the number of substituents. However, free energy calculations indicated kinetic and thermodynamic deviations, suggesting that the substituents directly affected the two hydroxyl groups—the reaction sites of 2PCET—as well as their solvation environment.

The remarkable applications of the nonfullerene acceptors (NFAs) make them highly favorable for commercialization as the organic photovoltaic materials. Herein, new perylene diimide-based compounds (PDFD1–PDFD9) with A₁–π–A₂–π–A₁ configuration were structurally designed by altering the π–bridges and end-capped acceptors for efficient perovskite materials for organic solar cells (OSCs). Density functional theory (DFT) and time-dependent DFT (TD-DFT) approach were employed to calculate the photophysical, optoelectronic and photovoltaic properties of the designed molecules. The results showed that these chromophores exhibited remarkably reduced E_gap (2.36–3.05 eV) and red-shifted absorption (λ_max) values, that is, 462–752 nm in the gas and 475–756 nm in the chloroform solvent phases. Moreover, the transition density matrix (TDM) plots along with the lower exciton binding energies (0.44–0.74 eV) showed efficient charge separation and recombination, which demonstrated significant charge transfer (CT). Furthermore, the donor: acceptor complex (PBDB-T:PDFD8) revealed prominent charge shift from the HOMO to LUMO. Among the proposed organic chromophores, the compound (PDFD8) showed the most promising results, that is, least E_gap (2.36 eV) and highest λ_max (756 nm). From the photovoltaic insights, significant results of the open-circuit voltage (V_oc) were obtained for these compounds. Therefore, these compounds exhibited outperforming attributes due to which they can serve as suitable electron transport materials (ETMs) for solar cell applications.

Formation of carbon–carbon bonds is the main tool for building skeletons of organic compounds. This review article endeavors primarily toward the development of sustainable synthetic tactics to build up new carbon–carbon bonds by electrochemical approaches. During the electrochemical formation of carbon–carbon bonds, Barbier-like addition protocols are only included in the review. Among the Barbier-like reactions, the addition of allylic and propargylic moieties to the different electrophilic centers is incorporated. These electrochemical processes have several obvious advantages, including simplicity, effectiveness, and environmental friendliness.

Methyl pyropheophorbide-a, one of the chlorophyll-a derivatives, was reacted with thallium(III) trifluoroacetate in tetrahydrofuran at room temperature to yield the corresponding Tl(III) complex with trifluoroacetate as an axial ligand. The anionic trifluoroacetate ligand was readily exchanged for chloride by treatment with brine. The resulting five-coordinated complex with Cl⁻ was fully characterized by ¹H NMR and visible absorption spectroscopies as well as mass spectrometry. Notably, the meso-protons of trifluoroacetate and chloride complexes coupled strongly with the stable Tl isotopes (the nuclear spin quantum numbers = 1/2) through four bonds to give doublet peaks (the coupling constants = 40–58 Hz). Their ¹H NMR spectra in deuterated chloroform indicated that the Tl(III) chlorins with an axial ligand were epimeric mixtures around the chiral central metal. Molecular model calculation proposed their absolute configurations at the asymmetric Tl(III) atom. The α-ligated complexes were estimated to be preferable over the β-ligated epimers. The epimeric ratios varying from 1.6 to 2.0 were dependent on the axial ligands. The obtained Tl(III) complex in dichloromethane efficiently absorbed violet and red lights but hardly emitted red-to-far-red light due to the heavy atom effect.

UV–Vis and X-ray crystallographic measurements, together with the analysis of the potential energy surfaces, demonstrated a critical role of halogen-bonded (HaB) complexes in the electron transfer (ET) reactions between diiodine and aromatic amines. Specifically, UV–Vis spectral studies showed that the addition of I₂ to solutions of tetramethyl-p-phenylenediamine (TMPD) or various N,N-dimethylanilines resulted in the immediate formation of HaB complexes. In systems with TMPD, this was followed by rapid ET—even at −85°C—resulting in the formation of persistent TMPD^+• cation radicals (which were crystallized as salts with iodide counterions). The formation of HaB complexes upon mixing I₂ with dimethylanilines was followed by the generation of I₃⁻, indicating the occurrence of redox processes. Subsequent chemical reactions led to the crystallization of triiodide salts of protonated m-methoxy-N,N-dimethylaniline, p-iodo-N,N-dimethylaniline (from the reaction with N,N-dimethylamine), or, surprisingly, 4,4′-bis(dimethylamino)benzhydrylium cations (from the reaction of I₂ with p-bromo-N,N-dimethylaniline). Most notably, the rates of the redox processes in all these systems were many orders of magnitude faster than those predicted by the classical Marcus (outer-sphere) ET theory. These high rates were accounted for by considering the donor–acceptor electronic coupling in the HaB precursor complexes, which drastically lowers the activation barriers for inner-sphere ET. These results confirm that HaB complexes are vital intermediates in the ET reactions of halogenated electrophiles, and their role should be taken into account when analyzing potential ET steps in chemical transformations involving such molecules.

In this study, synthesis, characterization, photophysical properties, and DFT calculations of a new tetraaryl-1,4-dihydropyrrolo[3,2-b]pyrrole (TAPP) derivative molecule of A-π-D-π-A type containing benzoxazole as an acceptor group at 1,4-positions have been carried out. The target A-D-A type molecule was synthesized using 4-(benzo[d]oxazol-2-yl)aniline by the method known in the literature, and it was aimed to obtain the classical TAPP structure in an iron-catalyzed environment. No product was obtained with the first method; therefore, the reaction conditions were optimized. The reaction time and temperature were varied in a controlled manner; the optimum conditions were determined with a reaction time of 7 h at 60°C. The photophysical behavior of the synthesized benzoxazole-substituted TAPP derivative was investigated by UV–vis and fluorescence spectroscopy depending on different solvent polarities. In the absorption spectra, the maximum absorption band observed around 330 nm in low polarity solvents shifted to 340 nm in polar solvents. Similarly, fluorescence emissions systematically red-shifted from hexane to DCM (470–550 nm), and quantum yields decreased significantly (0.41 in hexane and 0.03 in DCM). This bathochromic shift and decrease in intensity indicate that the molecule has high polarity in the excited state whereas the intrinsic charge transfer (ICT) and twisted ICT (TICT) states stabilize with increasing solvent polarity. At the same time, nonluminescent transition channels such as loss of planarity, oxygen-induced quenching, and internal conversion in the solvent-excited state also decrease the fluorescence intensity. The findings reveal that this TAPP derivative forms a strong donor-acceptor system and exhibits high sensitivity to solvent environment.