High-Performance Ultraviolet Organic Light-Emitting Diodes Enabled by Double Boron-Oxygen-Embedded Benzo[m]tetraphene Emitters.

Ultraviolet organic light-emitting diodes (UV OLEDs) have attracted increasing attention because of their promising applications in healthcare, industry, and agriculture; however, their development has been hindered by the shortage of robust UV emitters. Herein, we embedded double boron-oxygen units into nonlinear polycyclic aromatic hydrocarbons (BO-PAHs) to regulate their molecular configurations and excited-state properties, enabling novel bent BO-biphenyl (BO-bPh) and helical BO-naphthyl (BO-Nap) emitters with hybridized local and charge-transfer (HLCT) characteristics. They could be facilely synthesized in gram-scale amounts via a highly efficient two-step route. BO-bPh and BO-Nap showed strong UV and violet-blue photoluminescence in toluene with full width at half-maximum values of 25 and 37 nm, along with quantum efficiencies of 98 and 99%, respectively. A BO-bPh-based OLED showed high color purity UV electroluminescence peaking at 394 nm with Commission Internationale de l'Eclairage (CIE) coordinates of (0.166, 0.021). Moreover, the device demonstrated a record-high maximum external quantum efficiency (EQE) of 11.3%, achieved by successful hot exciton utilization. This work demonstrates the promising potential of double BO-PAHs as robust emitters for future UV OLEDs.

Mechanistic Insights into Oxidation of Benzaldehyde by Co-Peroxo Complexes.

Transition metal-peroxide complexes play a crucial role as intermediates in oxidation reactions. To unravel the mechanism of benzaldehyde oxidation by the Co-peroxo complex, we conducted density functional theory (DFT) calculations. The identified competing mechanisms include nucleophilic attack and hydrogen atom transfer (HAT). The nucleophilic attack pathway involves Co-O cleavage and nucleophilic attack, leading to the formation of the benzoate product. And the HAT pathway comprises O-O cleavage and HAT, ultimately resulting in the benzoate product. DFT calculations revealed that the formation of the end-on Co-superoxo complex 2 through Co-O cleavage, starting from the side-on Co-peroxo complex 1, is much more favorable than the formation of the two-terminal oxyl-radical intermediate 3 through O-O cleavage. Compared with the nucleophilic attack of benzaldehyde by 2, the abstraction of a hydrogen atom from benzaldehyde by 3 requires higher energy. The nature of the nucleophilicity of 2 and 3 accounts for the reactivity of the reaction.

Pt-S Bond-Enabled Temperature-Dependent Phosphorescence in S-Heteroaryl Tetradentate Pt(S

This study presents the rare examples of S-heteroaryl tetradentate Pt(S^C^N^O) luminescent complexes (PtSZ and PtSZtBu) containing a Pt-S bond. The presence of the Pt-S bond allows the novel Pt(S^C^N^O) complexes to exhibit temperature-dependent phosphorescent emission behavior. The PtSZtBu exhibits dual-emission phenomena and biexponential transient decay spectra above 250 K, indicating the presence of two minimal excited states in the potential energy surface (PES) of the T1 state. Through complementary experimental and computational studies, we have identified changes in orbital composition between Pt(dxy)-S(px) and Pt(dyz)-S(pz) in excited states with increasing temperature. This results in two energy minima, enabling the excited states to decay selectively and radiatively at different temperatures. Consequently, this leads to remarkable steady-state and transient emission spectra changes. Our work not only provides valuable insights for the development of novel Pt-S bond-based tetradentate Pt(II) complexes but also enhances our understanding of the distinctive properties governed by the Pt-S bond.

Perimidocarbene-Based Tetradentate Platinum(II) Complexes with an Unexpectedly Negligible 3MLCT Character.

Two novel six-membered perimidocarbene (PIC)-based tetradentate Pt(II) complexes were designed and successfully synthesized. Systematical experimental and theoretical studies suggest that the PIC moiety greatly affects the frontier orbitals, as well as the photophysical and excited-state properties of the Pt(II) complexes. PtYK2 has a broad emission spectrum peaking at 576 nm with a shoulder band at 620 nm, along with a full width at half-maximum (FWHM) value of 100.0 nm at 77 K in 2-MeTHF; however, the emission spectrum is slightly red-shifted with a dominant peak at 610 nm and a FWHM value of 125.0 nm at room temperature in a poly(methyl methacrylate) (PMMA) film. Time-dependent-density functional theory and natural transition orbital analyses reveal that PtYK2 has a 3LC (3πPIC* → πPIC)-dominated character with an unexpectedly negligible contribution of 3MLCT transition (0.68%) in the T1 state, which results in a broad emission spectrum and a relatively low quantum efficiency of 7.4% in the PMMA film.

Molecular Dynamics of Iron Porphyrin-Catalyzed C-H Hydroxylation of Ethylbenzene.

Quasi-classical molecular dynamics (MD) simulations were carried out to study the mechanism of iron porphyrin-catalyzed hydroxylation of ethylbenzene. The hydrogen atom abstraction from ethylbenzene by iron-oxo species is the rate-determining step, which generates the radical pair of iron-hydroxo species and the benzylic radical. In the subsequent radical rebound step, the iron-hydroxo species and benzylic radical recombine to form the hydroxylated product, which is barrierless on the doublet energy surface. In the gas-phase quasi-classical MD study on the doublet energy surface, 45% of the reactive trajectories lead directly to the hydroxylated product, and this increases to 56% in implicit solvent model simulations. The percentage of reactive trajectories leading to the separated radical pair is 98-100% on high-spin (quartet/sextet) energy surfaces. The low-spin state reactivity dominates in the hydroxylation of ethylbenzene, which is dynamically both concerted and stepwise, since the time gap between C-H bond cleavage and C-O bond formation ranges from 41 to 619 fs. By contrast, the high-spin state catalysis is an energetically stepwise process, which has a negligible contribution to the formation of hydroxylation products.

Mechanistic Investigation of Ni-Catalyzed Reductive Cross-Coupling of Alkenyl and Benzyl Electrophiles.

Mechanistic investigations of the Ni-catalyzed asymmetric reductive alkenylation of N-hydroxyphthalimide (NHP) esters and benzylic chlorides are reported. Investigations of the redox properties of the Ni-bis(oxazoline) catalyst, the reaction kinetics, and mode of electrophile activation show divergent mechanisms for these two related transformations. Notably, the mechanism of C(sp3) activation changes from a Ni-mediated process when benzyl chlorides and Mn0 are used to a reductant-mediated process that is gated by a Lewis acid when NHP esters and tetrakis(dimethylamino)ethylene is used. Kinetic experiments show that changing the identity of the Lewis acid can be used to tune the rate of NHP ester reduction. Spectroscopic studies support a NiII-alkenyl oxidative addition complex as the catalyst resting state. DFT calculations suggest an enantiodetermining radical capture step and elucidate the origin of enantioinduction for this Ni-BOX catalyst.

8-Phenylquinoline-Based Tetradentate 6/6/6 Platinum(II) Complexes for Near-Infrared Emitters.

A series of novel tetradentate 6/6/6 Pt(II) complexes containing an 8-phenylquinoline-benzo[d]imidazole-carbazole ligand was designed; the Pt(II) complexes could be synthesized by metalizing the corresponding ligand with K2PtCl4 in high isolated yields of 60-90%. Experimental and theoretical studies suggested that the ligand modification of the quinoline moieties of the Pt(II) complexes could tune their electrochemical, photophysical, and excited-state properties. Notably, all the Pt(II) complexes exhibited highly electrochemical stabilities with reversible redox processes except the quasi-reversible reduction of PtYL3. The large π-conjugation of the ligand together with increased metal-to-ligand charge-transfer (3MLCT) characters in T1 states enabled the Pt(II) complexes to show broad Gaussian-type NIR emission spectra with high photoluminescence quantum efficiencies of 1.2-1.5% and short τ of 0.8-1.5 µs in dichloromethane at room temperature. This work should provide a valuable reference for the design and development of monomer NIR emitters.

Deep transfer learning for predicting frontier orbital energies of organic materials using small data and its application to porphyrin photocatalysts.

Machine learning (ML) models have received increasing attention as a new approach for the virtual screening of organic materials. Although some ML models trained on large databases have achieved high prediction accuracy, the application of ML to certain types of organic materials is limited by the small amount of available data. On the other hand, metalloporphyrins and porphyrins (MpPs) have received increasing attention as potential photocatalysts, and recent studies have found that both HOMO/LUMO energy levels and energy gaps are important factors controlling the MpP photocatalysts. Since the training data of MpPs are insufficient and limited to porphyrin-based dyes, in this study, we proposed a deep transfer learning approach to rapidly predict the HOMO/LUMO energy levels and energy gaps of MpPs. To complement the open-source Porphyrin-based Dyes Database (PBDD), we curated a new database, the Metalloporphyrins and Porphyrins Database (MpPD), in which MpPs were specifically designed as potential photocatalysts and the HOMO/LUMO energies were calculated by advanced DFT functionals. We proposed PorphyBERT, a BERT-based regression model that was pre-trained with PBDD and fine-tuned with MpPD. The model performed satisfactorily in predicting HOMO and LUMO energies and energy gap with RMSEs of 0.0955, 0.0988, and 0.0787 eV and MAEs of 0.0774, 0.0824, and 0.0549 eV. Furthermore, due to its unique unsupervised pre-training phase, the model is not affected by the difference in computational functionals between pre-training and fine-tuning databases. Finally, we recommended 12 MpPs as potential photocatalysts for CO2 reduction with out-of-sample model predictions of energy gaps close to the values calculated by DFT.

Computational Exploration of Dirhodium Complex-Catalyzed Selective Intermolecular Amination of Tertiary vs. Benzylic C-H Bonds.

The mechanism and origins of site-selectivity of Rh2(S-tfpttl)4-catalyzed C(sp3)-H bond aminations were studied using density functional theory (DFT) calculations. The synergistic combination of the dirhodium complex Rh2(S-tfpttl)4 with tert-butylphenol sulfamate TBPhsNH2 composes a pocket that can access both tertiary and benzylic C-H bonds. The nonactivated tertiary C-H bond was selectively aminated in the presence of an electronically activated benzylic C-H bond. Both singlet and triplet energy surfaces were investigated in this study. The computational results suggest that the triplet stepwise pathway is more favorable than the singlet concerted pathway. In the hydrogen atom abstraction by Rh-nitrene species, which is the rate- and site-selectivity-determining step, there is an attractive π-π stacking interaction between the phenyl group of the substrate and the phthalimido group of the ligand in the tertiary C-H activation transition structure. By contrast, such attractive interaction is absent in the benzylic C-H amination transition structure. Therefore, the DFT computational results clearly demonstrate how the synergistic combination of the dirhodium complex with sulfamate overrides the intrinsic preference for benzylic C-H amination to achieve the amination of the nonactivated tertiary C-H bond.

P/N-Heteroleptic Cu(I)-Photosensitizer-Catalyzed [3 + 2] Regiospecific Annulation of Aminocyclopropanes and Functionalized Alkynes.

We report here a regiospecific [3 + 2] annulation between aminocyclopropanes and various functionalized alkynes enabled by a P/N-heteroleptic Cu(I) photosensitizer under photoredox catalysis conditions. Thus, a divergent construction of 3-aminocyclopentene derivatives including methylsulfonyl-, arylsulfonyl-, chloro-, ester-, and trifluoromethyl-functionalized aminocyclopentenes could be achieved with advantages of high regioselectivity, broad substrate compatibility, and mild and environmentally benign reaction conditions.

Fused 6/5/6 Metallocycle-Based Tetradentate Pt(II) Emitters for Efficient Green Phosphorescent OLEDs.

Pt(II) complexes are promising phosphorescent materials for organic light-emitting diode (OLED) applications in the fields of display, lighting, healthcare, aerospace, and so on. A series of novel biphenyl (bp)-based tetradentate 6/5/6 Pt(II) emitters using oxygen or carbon as a linking atom was designed and developed. The intermolecular interactions in crystal packing, electrochemical, and photophysical properties of the bp-based Pt(II) emitters and also their excited-state properties were systematically studied, which could be effectively regulated by ligand modification through linking group control; however, their emission spectra nearly showed no change. All the bp-based Pt(II) emitters exhibited vibronically featured emission spectra with dominant peaks at 502-505 nm and photoluminescent quantum yields of 24-34% in dichloromethane solution. Green OLED using Pt(bp-12) as an emitter achieved a maximum brightness (Lmax) of 16,644 cd/m2.

Mechanistic Investigation of Palladium-Catalyzed meta-C-H Bond Activation of Arenes with a Carboxyl Directing Group.

The mechanism of Pd(II)-catalyzed meta-C-H bond olefination of arenes with a carboxyl directing group (DG)-containing template has been investigated with density functional theory. The reaction includes three major steps: C-H bond activation, alkene insertion, and ß-hydride elimination. The C-H activation step, which proceeds via a concerted metalation-deprotonation pathway, is found to be the rate- and regioselectivity-determining step. We proposed a mono-N-protected amino acid (MPAA)/DG-assisted C-H activation model, in which the carboxyl DG coordinates with the Pd center and delivers it to the meta-position of arene, and the bidentate dianionic MPAA acts as a base for deprotonation. There is a hydrogen bonding interaction between the carboxyl DG and the carboxylate group of MPAA. An alternative Pd(OAc)2-catalyzed mechanism without involvement of MPAA is also operative. The template is conformationally flexible, and multiple low-energy transition-state conformations contribute to the regioselectivity.

Tetradentate Platinum(II) and Palladium(II) Complexes Containing Fused 6/6/6 or 6/6/5 Metallocycles with Azacarbazolylcarbazole-Based Ligands.

A series of novel tetradentate Pt(II) and Pd(II) complexes containing fused 6/6/6 or 6/6/5 metallocycles employing azacarbazolylcarbazole (ACzCz)-based ligands was developed. Systematic experimental and theoretical studies suggest that both the ligand structures and the central metal ions have great influences on the electrochemical and photophysical properties of the complexes. The time-dependent density functional theory (TD-DFT) calculations and natural transition orbital (NTO) analyses reveal that the Pt(II) complexes possess 10.8-15.2% metal-to-ligand charge transfer (3MLCT) mixed with ligand-centered (3LC) characters, by contrast, the Pd(II) complexes exhibit significantly decreased 4.2-7.1% 3MLCT characters and enhanced 3LC compositions. All of the Pt(II) and Pd(II) complexes possess various channels for the intersystem crossing (ISC) on the basis of small energy gaps ΔES1-Tn and matching transition orbital compositions; moreover, Pd(ACzCz-1) and Pd(ACzCz-2) also possess efficient reverse intersystem crossing (RISC) to show both delayed fluorescence (DF) and phosphorescence in PMMA films at room temperature (RT). Pt(ACzCz-3) has ΦPL values of 57% with a τ of 5.1 µs in dichloromethane at RT and 50% with 3.9 µs in PMMA at RT. Notably, Pd(ACzCz-1) exhibits ultralong low-temperature phosphorescence with a τ of 1307 µs. Pt(ACzCz-2)-based green OLED employing 26mCPy as the host demonstrated a peak EQE of 8.2% and a Lmax of 24065 cd/m2.

Conversion of amides to esters by the nickel-catalysed activation of amide C-N bonds.

Amides are common functional groups that have been studied for more than a century. They are the key building blocks of proteins and are present in a broad range of other natural and synthetic compounds. Amides are known to be poor electrophiles, which is typically attributed to the resonance stability of the amide bond. Although amides can readily be cleaved by enzymes such as proteases, it is difficult to selectively break the carbon-nitrogen bond of an amide using synthetic chemistry. Here we demonstrate that amide carbon-nitrogen bonds can be activated and cleaved using nickel catalysts. We use this methodology to convert amides to esters, which is a challenging and underdeveloped transformation. The reaction methodology proceeds under exceptionally mild reaction conditions, and avoids the use of a large excess of an alcohol nucleophile. Density functional theory calculations provide insight into the thermodynamics and catalytic cycle of the amide-to-ester transformation. Our results provide a way to harness amide functional groups as synthetic building blocks and are expected to lead to the further use of amides in the construction of carbon-heteroatom or carbon-carbon bonds using non-precious-metal catalysis.

Computational Studies on the Mechanism and Origin of the Different Regioselectivities of Manganese Porphyrin-Catalyzed C-H Bond Hydroxylation and Amidation of Equilenin Acetate.

The manganese porphyrin-catalyzed C-H bond hydroxylation and amidation of equilenin acetate developed by Breslow and his co-worker have been investigated with density functional theory (DFT) calculations. The hydroxylation of C(sp2)-H bond of equilenin acetate leading to the 6-hydroxylated product is more favorable than the hydroxylation of C(sp3)-H bond of equilenin acetate, leading to the 11ß-hydroxylation product. The computational results suggest that the C(sp2)-H bond hydroxylation of equilenin acetate undergoes an oxygen-atom-transfer mechanism, which is more favorable than the C(sp3)-H bond hydroxylation undergoing the hydrogen-atom-abstraction/oxygen-rebound (HAA/OR) mechanism by 1.6 kcal/mol. That is why, the 6-hydroxylated product is the major product and the 11ß-hydroxylated product is the minor product. In contrast, the 11ß-amidated product is the only observed product in manganese porphyrin-catalyzed amidation reaction. The benzylic amidation undergoes a hydrogen-atom-abstraction/nitrogen-rebound (HAA/NR) mechanism, in which hydrogen atom abstraction is followed by nitrogen rebound, leading to the 11ß-amidated product. The benzylic C(sp3)-H bond amidation at the C-11 position is more favorable than aromatic amidation at the C-6 position by 4.9 kcal/mol. Therefore, the DFT computational results are consistent with the experiments that manganese porphyrin-catalyzed C-H bond hydroxylation and amidation of equilenin acetate have different regioselectivities.

Phosphorescent Tetradentate Platinum(II) Complexes Containing Fused 6/5/5 or 6/5/6 Metallocycles.

A series of phenylpyridine (ppy)-based 6/5/5 N*C^N^O and biphenyl (bp)-based 6/5/6 N*C^C*N Pt(II) complexes employing tetradentate ligands with nitrogen or oxygen atoms as bridging groups have been developed. Ligand structural modifications have great influences on the electrochemical, photophysical, and excited-state properties, as well as photostabilities of the Pt(II) complexes, which were systematically studied by experimental and theoretical investigations. The time-dependent density functional theory calculations and natural transition orbital analyses reveal that Pt(bp-6), Pt(bp-7), and Pt(bp-8) have dominant ligand-centered (3LC) mixed with small metal-to-ligand charge-transfer (3MLCT) characters in T1 states, resulting in relatively low quantum efficiencies (ΦPL) of 5-33% and 12-32% in dichloromethane solution and PMMA film, respectively. By contrast, Pt(ppy-1) possesses much more 3MLCT character in the T1 state, enabling a high ΦPL of 95% in dichloromethane and 90% in DPEPO film, and large radiative decay rates. The strength of the Pt-N1 coordination bond plays a critical role in the photostability. Pt(ppy-1)- and Pt(bp-6)-doped polystyrene films demonstrate long photostability lifetimes of 150 min for LT97 and LT98.5, respectively. A Pt(ppy-1)-based green OLED using 26mCPy as host realized a peak EQE of 18.5%, which still maintained an EQE of 10.4% at 1000 cd/m2, and an Lmax of over 40 000 cd/m2 was achieved. This study should provide a valuable reference for the further development of efficient and stable phosphorescent Pt(II) complexes.

Highly Efficient Phosphorescent Tetradentate Platinum(II) Complexes Containing Fused 6/5/6 Metallocycles.

A series of neutral tetradentate Pt(II) complexes with fused 6/5/6 metallocycles and biphenyl (bp)-containing ligands have been designed and synthesized. All bridging atoms adopt nitrogens designed as an acridinyl group (Ac), an aza acridinyl group (AAc), and an aza carbazolyl group (ACz), which can effectively tune their LUMO energy levels. Their HOMO energy levels can be well-controlled through molecular modifications on the bp moieties with electron-donating and electron-withdrawing groups. These molecular modifications also have profound effects on the electrochemical and photophysical properties and photostabilities of the Pt(II) complexes. The ground-states and excited states are systematically studied by density functional theory (DFT), time-dependent density functional theory (TD-DFT), and natural transition orbital (NTO) calculations. All the Pt(II) complexes exhibit admixed 3(LC/MLCT) characters in T1 states with various proportions, which are strongly structure-dependent. These 6/5/6 Pt(II) complexes demonstrate high quantum efficiencies in dichloromethane solutions (ΦPL = 27-51%) and in doped PMMA films (ΦPL = 36-52%) at room temperature with short luminescence lifetimes of 1.6-9.5 µs and 7.6-9.0 µs, respectively. They emit green light with dominant peaks of 512-529 nm in solutions and 512-524 nm in doped PMMA films, respectively. Importantly, Pt(bp-2) exhibits highly stable emission colors with the same dominant peaks at 512 nm in various matrixes and also demonstrates a long photostability lifetime, LT80, at 80% of initial luminance, of 190 min, which is doped in polystyrene films (5 wt %) excited by UV light of 375 nm at 500 W/m2. These studies indicate that these 6/5/6 Pt(II) complexes can act as good phosphorescent emitters for OLED applications and should provide a viable route for the development of efficient and stable Pt(II)-based phosphorescent emitters.

Tuning the Excited State of Tetradentate Pd(II) Complexes for Highly Efficient Deep-Blue Phosphorescent Materials.

Deep-blue-light-emitting materials are urgently desired in high-performance organic light-emitting diodes (OLEDs) for full-color display and solid-state lighting applications. However, the development of stable and efficient deep-blue emitters remains a great challenge. Herein, a series of stable and efficient tetradentate Pd(II)-complex-based deep-blue emitters with rigid 5/6/6 metallocycles and no F atom were designed and synthesized. These deep-blue emitters employ various isoelectronic five-membered heteroaryl-ring-containing ligands to exhibit extremely narrow emission spectra peaking at 439-443 nm with a full width at half-maximum (fwhm) of only 22-38 nm in 2-methyltetrahydrofuran at room temperature. In particular, the design of an intramolecular hydrogen bond enabled the 1-phenyl-1,2,3-trazole-based Pd(II) complexes to achieve CIEy < 0.1 (0.069-0.078; CIE is Commission Internationale de L'Eclairage). Theoretical calculation and natural transition orbital analysis reveal that these deep-blue materials emit light exclusively from their ligand (carbazole)-centered (3LC) states. Moreover, the triplet excited-state property can be efficiently regulated through ligand modification with isoelectronic oxazole and thiazole rings or pyridine rings, resulting in sky-blue-to-yellow materials, which emit light originating from an admixture of metal-to-ligand charge-transfer (3MLCT) and intraligand charge-transfer states. The newly developed Pd(II) complexes are strongly emissive in various matrixes with a quantum efficiency of up to 51% and also highly thermally stable with a 5% weight-reduction temperature (ΔT5%) of up to 400 °C. Deep-blue OLEDs with CIEy < 0.1 employing Pd(II) complexes as emitters were successfully fabricated for the first time. This study demonstrates that the Pd(II) complexes can act as excellent phosphorescent light-emitting materials through rational molecular design and also provide a valuable method for the development of Pd(II)-complex-based efficient and stable deep-blue emitters.

Understanding the structures and aromaticity of heteroporphyrins with computations.

Heteroporphyrins are porphyrin derivatives with replacement of the pyrrolic NH moiety by other heteroatom-containing groups, such as PH, AsH, SiH2, O, S, etc. For all studied heteroporphyrins, the macrocycle structure is distorted due to the presence of large heteroatoms. The HOMO-LUMO gap of heteroporphyrins is generally decreased compared to regular porphyrins. Both nucleus independent chemical shifts values and visualized anisotropy of induced current density were computed to describe the aromaticity of heteroporphyrins. The plots of anisotropy of induced current density suggest that the ring current diverged into an outer and an inner pathway at each ring. The current mainly passes through the outer path at the pyrrolic rings with inner hydrogen and through the inner path at the pyrrolic rings without inner hydrogen. In both regular porphyrin and O-substituted heteroporphyrins, the aromatic pathway is mainly contributed by the 22π-electron aromatic route model. Heteroatoms such as PH, AsH, S, Se and Te have little contribution to the aromaticity of heteroporphyrins. In addition, the π conjugation is also interrupted at the CH2 and SiH2 moiety, and the ring current mainly passes through the outer path of the heteroporphyrins with CH2 and SiH2 replacing the pyrrolic NH moiety. Therefore the 18π-[18]annulene model is dominated in PH-, AsH-, S-, Se-, Te-, CH2- and SiH2-substituted heteroporphyrins. These computational studies shed new light on the aromatic characters of heteroporphyrins, and will facilitate the further development of various novel heteroporphyrins.

Mechanism and stereoselectivity of benzylic C-H hydroxylation by Ru-porphyrin: a computational study.

The mechanism and origin of the stereoselectivity of asymmetric benzylic C-H hydroxylation by Ru-porphyrin were elucidated with density functional theory calculations. The reaction proceeds via a hydrogen-atom abstraction/oxygen-rebound pathway, wherein a high-valent ruthenium-oxo species abstracts a hydrogen atom from ethylbenzene to generate a radical pair intermediate, followed by the oxygen-rebound process to form 1-phenylethanol. The hydrogen-atom abstraction step is the rate- and stereoselectivity-determining step. Based on the mechanistic model, the computed stereoselectivity is in agreement with the experimental observations. Analysis of the distortion/interaction model suggests that stereoselectivity is determined by both the distortion energy of the ethylbenzene and the interaction energy between the ethylbenzene and the chiral Ru-porphyrin. The steric repulsion between the phenyl group of ethylbenzene and the bulky substituent of Ru-porphyrin is the leading cause of chiral induction.