Journal of Physical Organic Chemistry最新文献

Triplet–triplet annihilation upconversion (TTA-UC) is a promising strategy for converting low-energy photons into high-energy photons. Among emitter molecules, 9,10-diphenylanthracene (DPA) is widely used owing to its rigid aromatic structure, high fluorescence quantum yield (Φ_FL), and favorable triplet energy levels for efficient TTA-UC. However, only a few systematic studies have examined how chemical substitutions at the 4-positions of DPA affect their UC efficiency. Here, we investigate the effect of electron-donating and electron-accepting substituents at the 4-positions of DPA on its fluorescence and TTA-UC properties. DPA derivatives with substituents at the two 4-positions of the phenyl rings were synthesized. The fluorescence properties of solutions of these DPA derivatives and the TTA-UC properties of mixed solutions containing the DPAs and a sensitizer molecule were evaluated under a nitrogen atmosphere. The Φ_FL of DCl-DPA was the highest, followed by DCN-DPA. The UC quantum efficiency (η_UC) was estimated, with the highest value obtained for unsubstituted DPA, followed by DCl-DPA and DCN-DPA. Moreover, the saturated UC quantum efficiency (η_UC^∞), the quantum yield of triplet–triplet energy transfer, and the quantum yield of TTA (Φ_TTA) were also estimated. The results indicate that the Φ_TTA value primarily governs the η_UC^∞ values. These findings provide insight into the rational design of emitter molecules for optimizing TTA-UC efficiency.

Previous NMR ¹J(C13,H)–s correlations exhibited only marginal degrees of success. Presented here is a new such correlation where it is proposed NMR coupling data is passed by H–C–H and H–H pathways as suggested by the theoretical results of Provasi et al. Used where the current best values of the ¹J(C13,H)'s and molecular structure data for the hydrocarbons methane (1), ethane (2), ethene (3), benzene (4), propadiene (5), and ethyne (6). Simple equations for calculation of s character and bond angles are presented. The correlation has been extended to the case of a fluorine substituent. How the s character frameworks of molecules can be mapped out is demonstrated and compared to natural bond orbital (NBO) analysis estimations from density functional theory calculations. The definitions and calculation of the parameters in the master equation, ¹J(C13,H) = A s + n B + m C + o D + E + F, are explained in detail.

The results are reported of potential energy surface (PES) analyses of six symmetrical azines Y_p − Ph − RC=N − N=CR − Ph − Y_p, namely, the benzaldehyde azines 1H, 2H, and 8H with R = H and the acetophenone azines 1M, 2M, and 8M with R = Me. The Y substituents Cl (1), Br (2), and Me (8) were studied because sets of polymorphs I (C₂-symmetry, azine twist τ ≈ 135 ± 10°, disrotatory phenyl twists ϕ_i ≠ 0°) and II (C_i-symmetry, τ = 180°, conrotatory ϕ_i ≠ 0°) were crystallized for these three azines. The azine-Me groups in (E,E)-acetophenone azines cause steric strain with the N lone pairs, and this strain is reduced by small rotations about the Az-CH₃ bonds and geared phenyl twisting may lead to C₂- or C_i-structures. The in-depth exploration of the (τ, ϕ₁, ϕ₂) conformational space on the MP2(full)/6-311G* PES of 1M shows that the enantiomerization of C₂-1M to C₂-1M’ involves, first, one Ph twist inversion to a C_i-like structure, the subsequent inversion of the azine twist in, and the, second, Ph twist inversion on the path to C₂-1M’. The essential characteristics of this enantiomerization mechanism apply in general to disubstituted acetophenone azine.

Density functional theory (DFT) with the ωB97X-D exchange-correlation functional and the 6-311G(d,p) basis set together with the Bonding Evolution Theory (BET) have been enacted to unravel the mechanism of the catalytic aza-Wittig reaction leading to the formation of 2-methylbenzoxazole 3. The exploitation of the potential energy surface has shown that this reaction takes place following two main Channels, a and b, where favorable Channel a leads to the targeted product and takes place following four steps. A panoply of computational chemistry tools has been employed, leading to comprehensive and consistent results and interpretations: (i) BET analysis has highlighted the successive formation and breaking of chemical bonds leading to the synthesis of 3 and the liberation of a carbon dioxide molecule from the attack of phosphine oxide on the aryl isocyanate; (ii) moreover, BET has revealed that the synthesis of 3 takes place in four steps, with asynchronous transition states; (iii) characterized by large electron density transfers (larger than for the synthesis of the parent 2-methylbenzothiazole, owing to the larger electronegativity of the O vs. S atoms); (iv) the relative energies of the transition state and intermediate isomers have been substantiated by carrying out a NonCovalent Interaction (NCI) analysis, pointing out the role of specific H-bonds and π-π interactions; and (v) the key elements of this NCI analysis have further corroborated the results of the Distortion Interaction/Activation Strain (DIAS) approach.

The ruthenium complex catalyzed self-coupling reaction of secondary alcohols is an environmentally friendly strategy for the synthesis of β-branched ketones. In order to understand the reaction mechanism, a density functional theory (DFT) study was carried out using 1-phenylethanol as substrate. The catalytic cycle is mainly composed of three stages. The first stage is the dehydrogenation of 1-phenylethanol and hydrogen generation, the second stage is the self-coupling of aldehydes, and the third stage is hydrogenation of α,β-unsaturated ketone. DFT calculations indicate that 1-phenylethanol-assisted dehydrogenation is superior to direct dehydrogenation. The hydrogenation of α,β-unsaturated ketone via 1, 4-addition is more favorable than that via 1,2-addition, and the corresponding product is more stable. The mechanistic insights gained in this study would be helpful in improving the current reaction system or designing new catalysts.

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.