Smaller Rate Constants Research Articles

Room‐Temperature Afterglow Nanostructures via Block Copolymer Self‐Assembly

AbstractMiniaturization of organic afterglow materials has shown promising application in biomedical and other areas. Current technologies, such as nanoprecipitation, mechanical treatment, and emulsion polymerization, lack the capability of facile control on the morphology and dimension of the miniaturized organic afterglow materials. Here we report the fabrication of organic afterglow nanostructures via block copolymer self‐assembly at room temperature. The fabrication is based on two‐component design strategy where hydrophobic luminescent emitters with small rate constants of phosphorescence decay or reverse intersystem crossing are designed as the first component. Amphiphilic block copolymers that can form spherical core‐shell micelles and worm‐like micelles with glassy hydrophobic cores are used as the second component. Upon addition of water into a dimethylformamide solution that contains the two components, the amphiphilic block copolymers self‐assemble into well‐defined nanostructures and accommodate the hydrophobic luminescent emitters in nanostructure's hydrophobic cores. After switching to pure water by dialysis, room‐temperature afterglow nanostructures have been obtained because of the excellent protection of organic triplets by the glassy hydrophobic cores. The afterglow nanostructures exhibit intriguing afterglow mechanism modulated by the types of luminescent emitters, controlled dimensions and morphologies by the structural parameters of the block copolymers.

Transformation of organic afterglow mechanism from room-temperature phosphorescence to thermally-activated delayed fluorescence in intramolecular charge transfer systems

Organic afterglow materials have emerged as an important class of luminescent materials. These afterglow systems feature small rate constants of key photophysical processes, such as phosphorescence decay and nonradiative decay of triplet excited states. When coupled to other photophysical processes, these afterglow systems would give rise to intriguing photophysical behaviors. Here we report the transformation of afterglow mechanism from room-temperature phosphorescence (RTP) to thermally-activated delayed fluorescence (TADF) in intramolecular charge transfer (ICT) systems. Detailed studies reveal that the increase of the acceptor strength of ICT molecules can reduce singlet-triplet splitting energy and consequently open reverse intersystem crossing (RISC) pathway with moderate kRISC of 1–10 s−1 to harvest triplet energies, leading to the RTP-to-TADF afterglow transformation. Such observations provide deep understanding on the behaviors of organic triplets with small photophysical rate constants. Besides, these organic ICT molecules have been incorporated into aqueous emulsion systems to exhibit promising applications.

Kinetics of Na- and K- uranyl arsenate dissolution

We integrated aqueous chemistry analyses with geochemical modeling to determine the kinetics of the dissolution of Na and K uranyl arsenate solids (UAs(s)) at acidic pH. Improving our understanding of how UAs(s) dissolve is essential to predict transport of U and As, such as in acid mine drainage. At pH 2, Na0.48H0.52(UO2)(AsO4)(H2O)2.5(s) (NaUAs(s)) and K0.9H0.1(UO2)(AsO4)(H2O)2.5(s) (KUAs(s)) both dissolve with a rate constant of 3.2 × 10−7 mol m−2 s−1, which is faster than analogous uranyl phosphate solids. At pH 3, NaUAs(s) (6.3 × 10−8 mol m−2 s−1) and KUAs(s) (2.0 × 10−8 mol m−2 s−1) have smaller rate constants. Steady-state aqueous concentrations of U and As are similarly reached within the first several hours of reaction progress. This study provides dissolution rate constants for UAs(s), which may be integrated into reactive transport models for risk assessment and remediation of U and As contaminated waters.

Friedel-Crafts acylation of anisole with acetic anhydride over single- to multiple-layer MWW zeolites: Catalytic behavior and kinetic mechanism

Numerous efforts have been dedicated to develop solid acid catalysts with higher activity and stability replacing the homogeneous catalysis for Friedel-Crafts (FC) acylation reaction. In this study, single- to multiple-layer MWW zeolites are employed as well-defined model catalysts to investigate the influencing mechanism of microscale structure of MWW zeolites on the kinetics for acylation of anisole with acetic anhydride. It is found that the acylation of anisole is solely carried out on the external acid sites of MWW zeolites and follows Langmuir-Hinshelwood mechanism. The single-layer MWW (SL-MWW) with more external acid sites exhibits lower catalytic activity for acylation of anisole in batch reaction, whereas the recycle stability of SL-MWW is clearly higher than that of multiple-layer MWW (ML-MWW). Kinetics results reveal that a large equilibrium constant of product adsorption together with the confinement effect within 12MR pockets on surface of SL-MWW results in difficult desorption of product and small rate constant. Therefore, the favorable mass-transfer and diffusion of SL-MWW is restrained in batch reaction and at low temperature condition. Based on these findings, the continuous flow fixed-bed process under an elevated temperature (493 K) was conducted to underline the structural advantages of SL-MWW zeolite. The lifetime of SL-MWW can reach to 300 h in the optimal reaction conditions, which is potential catalyst for industrial application in the field of FC acylation reactions.

Unusually Kinetically Inert Monocationic Neptunyl Complex with a Fluorescein-Modified 1,10-Phenanthroline-2,9-dicarboxylate Ligand: Specific Separation and Detection in Gel Electrophoresis

We found a singly charged Np(V)O2+ complex with unprecedented kinetic inertness in aqueous solution, one million times slower than the widely accepted fast kinetics of neptunyl complexes. An inert NpO2+ complex with a fluorescent 1,10-phenanthroline-2,9-dicarboxylate derivative was found by kinetic selection using polyacrylamide gel electrophoresis (PAGE) from a small chemical library. Autoreduction from Np(VI)O22+ to Np(V)O2+ via complexation was observed. A remarkably small spontaneous dissociation rate constant of 8 × 10-6 s-1 (half-life of 23 h) was determined using PAGE. Selective detection of Np(V)O2+ was achieved in PAGE with a detection limit of 68 pmol dm-3 (17 fg). This system was successfully applied to simulated radioactive waste samples. Our finding that electron-rich NpO2+ forms a uniquely inert complex with no strong electrostatic interaction reveals a new aspect of actinide chemistry for developing a novel separation system of real radioactive material samples.

A thermodynamically consistent monte carlo cross-bridge model with a trapping mechanism reveals the role of stretch activation in heart pumping.

Changes in intracellular calcium concentrations regulate heart beats. However, the decline in the left ventricular pressure during early diastole is much sharper than that of the Ca2+ transient, resulting in a rapid supply of blood to the left ventricle during the diastole. At the tissue level, cardiac muscles have a distinct characteristic, known as stretch activation, similar to the function of insect flight muscles. Stretch activation, which is a delayed increase in force following a rapid muscle length increase, has been thought to be related to autonomous control in these muscles. In this numerical simulation study, we introduced a molecular mechanism of stretch activation and investigated the role of this mechanism in the pumping function of the heart, using the previously developed coupling multiple-step active stiffness integration scheme for a Monte Carlo (MC) cross-bridge model and a bi-ventricular finite element model. In the MC cross-bridge model, we introduced a mechanism for trapping the myosin molecule in its post-power stroke state. We then determined the rate constants of transitions for trapping and escaping in a thermodynamically consistent manner. Based on our numerical analysis, we draw the following conclusions regarding the stretch activation mechanism: (i) the delayed force becomes larger than the original isometric force because the population of trapped myosin molecules and their average force increase after stretching; (ii) the delayed force has a duration of more than a few seconds owing to a fairly small rate constant of escape from the trapped state. For the role of stretch activation in heart pumping, we draw the following conclusions: (iii) for the regions in which the contraction force decreases earlier than the neighboring region in the end-systole phase, the trapped myosin molecules prevent further lengthening of the myocytes, which then prevents further shortening of neighboring myocytes; (iv) as a result, the contraction forces are sustained longer, resulting in a larger blood ejection, and their degeneration is synchronized.

Organic Afterglow Emulsions Exhibiting 2.4 s Phosphorescence Lifetimes and Specific Protein Binding Property

AbstractAqueous afterglow dispersions display promising biomedical applications due to their long‐lived excited states, whereas it is a common problem in the research field that processing and transferring solid‐state afterglow materials into aqueous medium can cause significant drop and even complete loss of their afterglow properties. Here, aqueous afterglow dispersions are fabricated from liquid precursors by dopant–matrix strategy and emulsion polymerization, which avoids the processing procedures on solid‐state materials and achieves 2.4 s long phosphorescence lifetimes in aqueous medium. Luminescent difluoroboron β‐diketonate dopants are first designed with small rate constant of phosphorescence decay and then dissolved in monomers. After emulsion polymerization, the as‐formed polymer latex particles not only assist dopants’ intersystem crossing but also provide a glassy microenvironment to largely suppress nonradiative decay of dopants’ triplets, leading to in situ formation of aqueous afterglow dispersions. This provides a robust method for constructing afterglow emulsions with long‐term colloidal stability, relatively high solid contents, tunable sizes, and diverse compositions. Through emulsion copolymerization, afterglow emulsions decorated with specific ligands are obtained to exhibit specific protein binding properties. Such decorated afterglow emulsions address the issue that afterglow materials lack biorecognition property and can pave the way for their applications in immunoassay and immunoimaging.

Fate of the Gas-Phase Reaction Between Oxirane and the CN Radical in Interstellar Conditions

The escalating identification of new complex molecules in the interstellar medium claims for potential formation routes of such species. In this regard, the present work considers the reaction between oxirane and the CN radical as a feasible formation mechanism of species having the C3H3NO molecular formula. Indeed, the compounds of this family are elusive in the interstellar medium and suggestions on which species could be formed at low temperature and low pressure conditions might aid their discovery. The c-C2H4O + CN reaction has been investigated from the thermodynamic and kinetic points of view. The thermodynamic has been studied by means of a double-hybrid density functional and revealed the presence of several mechanisms submerged with respect to the reactants energy, with the potential formation of oxazole and cyanoacetaldehyde. However, the kinetic results suggest that the main reaction pathway is the H-extraction, leading to 2-oxiranyl radical and HCN. The formation of cyanoacetaldehyde + H and of H2CCN + H2CO is also possible with smaller rate constants, while the production of oxazole is negligible due to the presence of a high energy barrier.

Applicability of the second-order rate law for modeling dissolved O2 consumption by Fe(II)-bearing geologic media

Fe(II)-bearing geologic media are promising agents for the consumption of dissolved oxygen (DO) remaining in geologic formations after the backfilling of radioactive waste repositories, which helps prevent redox-sensitive radionuclides from becoming soluble and mobile in groundwater. A second-order rate law has been proposed to describe DO consumption due to the oxidation of structural Fe(II) at the mineral surface; however, it has only been tested against a few Fe(II)-bearing geologic media via DO consumption experiments. Thus, this study investigates the applicability of the second-order rate law to Fe(II)-bearing geologic media and minerals by reanalyzing data from previous batch experiments of DO consumption. Additional DO consumption experiments were also performed on diatomaceous and siliceous mudstones to examine the influence of clay components and coexisting Fe(II)-bearing minerals on the DO consumption rate constant. The reanalysis results showed that the second-order rate law can effectively describe DO consumption by both natural geologic media and purified minerals. The derived consumption rate constants are relatively similar for natural geologic media and purified minerals, but not for media with a high clay content. In particular, the rate constants for sedimentary rocks with smectite components exhibit large variations and tend to be smaller than the theoretical lower limit for structural Fe(II) on silicate minerals. Conversely, the rate constants for mudstones containing non-swelling chlorite exhibit small variations. This implies that, in batch experiments on powdered samples containing smectite, DO is consumed not only by structural Fe(II) at the external surface but also by Fe(II) in the interlayers of the smectite, which is less accessible to DO in bulk solution. This may explain the prolonged reaction time and relatively small rate constants of sedimentary rocks with smectite components. This study suggests that the second-order rate law can be applied to model DO consumption in a variety of Fe(II)-bearing rocks. However, the rate constants may be underestimated with large variations when testing powdered rocks containing smectite.

Kinetics and Mechanism of E. Coli Transcription Initiation

In transcription initiation, specific contacts between RNA polymerase (RNAP) and promoter DNA are disrupted as the RNA-DNA hybrid advances into the cleft, resulting in promoter escape of RNAP. From the pattern of large and small rate constants for steps of initiation at λPR promoter at 19°C, we proposed that in-cleft interactions are disrupted in extending 3-mer to 5-mer RNA, −10 interactions are disrupted in extending 6-mer to 9-mer, and −35 interactions are disrupted in extending 10-mer to 11-mer, allowing RNAP to escape.

Degradation of emerging pharmaceutical micropollutants in municipal secondary effluents by low-pressure UVC-activated HSO5− and S2O82− AOPs

Abstract The degradation of six representative emerging pharmaceuticals (PhACs) (carbamazepine (CBZ), crotamiton (CRMT), N,N-diethyl-meta-toluamide (DEET), gemfibrozil (GEM), ibuprofen (IBP) and trimethoprim (TMP)) mixture in municipal secondary effluents by UVC-activated HSO5− and S2O82− were investigated and compared to UV/H2O2 process. The results showed that the PhACs degradation efficiencies by UV/HSO5− were typically smaller than those obtained by UV/H2O2. In contrast, UV/S2O82− offered larger degradation efficiencies of CBZ, GEM, IBP and TMP in comparison to UV/H2O2, which however was less effective in degrading CRMT and DEET. The electron spin resonance (ESR) and radical scavenging tests indicated that hydroxyl radical (HO•) was the major reactive species responsible for the degradation of PhACs by UV/HSO5−, while both sulfate radical (SO4•−) and HO• contributed to PhACs degradation by UV/S2O82−. The rate constants of PhACs reacting with HO•/SO4•− were determined on the basis of their degradation kinetics. All PhACs have large rate constants with HO• over the range of (7.66–9.86) × 109 M−1 s−1. Among of them, CBZ, GEM, IBP and TMP have large rate constants with SO4•− at (1.48–4.59) × 109 M−1 s−1. However, CRMT and DEET have smaller rate constants with SO4•− at 2.84 × 108 and 2.95 × 108 M−1 s−1, respectively, thereby resulting in limited degradation efficiencies by UV/S2O82−. The degradation intermediates of PhACs were investigated and tracked by LC-QTOF-MS. Evolution of effluent organic matters (EfOM) was investigated by means of excitation-emission fluorescence matrices (EEFM), indicating successful destruction of EfOM by HO•/SO4•−. The reaction stoichiometric efficiencies (RSE) of Δdissolved organic carbon (DOC)/Δoxidants were compared, suggesting high oxidant utilization efficiencies for UV/HSO5− and UV/S2O82− at 66.8% and 52.0%, respectively.

Quantum dynamics study of isotope effects of the OD/OH + CH3 reactions

ABSTRACT A six-degrees-of-freedom, time-dependent quantum dynamics calculation is employed to study the integral cross sections, full-dimensional cumulative reaction probabilities and full-dimensional rate constants for the isotopic reactions of the OD and OH with CH3 reactions. The full-dimensional cumulative reaction probabilities and full-dimensional rate constants are obtained using the energy and J-K shifting approaches based on the six-degrees-of-freedom calculations. The comparison of integral cross sections shows that the OD + CH3 reaction has a larger energy threshold and a smaller tunnelling effect than the OH + CH3 reaction. The corrected rate constants using the experimental zero-point energy have a very good agreement with the experimental results. The comparison of the rate constants shows that the OD + CH3 has smaller rate constants than the OH + CH3 reaction, which indicates a smaller reactivity due to the isotope substitution.

Импеданс реакции выделения водорода по механизму Фольмера-Гейровского при различной форме зависимости теплоты адсорбции водорода от степени заполнения

The steady-state polarization curves and overpotential dependences of the equivalent circuit elements (R1, R2, C2) were calculated for the hydrogen evolution at nonlinear variation of the free energy of hydrogen adsorption DGadswith increasing coverage q. It was shown that the polarization curves depend weakly on the function g(q) = DGads/RT while the values of the Faradaic impedance parameters depend markedly on g(q). When DGads is coverage-dependent, the following differences from Langmuir adsorption are observed: (i) inductive behavior of impedance at small rate constant of the Heyrovsky reaction compared with rate constant of the Volmer reaction and at equal transfer coefficients of the steps; (ii) logR1–h curve is off parallel with logR2–h curve at high cathodic polarizations.

Determination of Proton-Coupled Electron Transfer Reorganization Energies with Application to Water Oxidation Catalysts.

The reorganization energy, λ, for interfacial electron transfer (ET) and for proton-coupled electron transfer (PCET) between a water oxidation catalyst and a conductive In2O3:Sn (ITO) oxide were extracted from kinetic data by application of Marcus-Gerischer theory. Specifically, light excitation of the water oxidation catalyst [RuII(tpy)(4,4'-(PO3H2)2-bpy)OH2]2+ (RuII-OH2), where tpy is 2,2':6',2″-terpyridine and bpy is 2,2'-bipyridine, anchored to a mesoporous thin film of ITO nanocrystallites resulted in rapid excited-state injection ( kinj > 108 s-1). The subsequent reaction of the injected electron (ITO(e-)) and the oxidized catalyst was quantified spectroscopically on nanosecond and longer time scales. The metallic character of ITO allowed potentiostatic control of the reaction free energy change -Δ Go over a 1 eV range. At pH values below the p Ka = 1.7 of the oxidized catalyst, ET was the primary reaction. Within the pH range 2 ≤ pH ≤ 5, an interfacial PCET reaction (ITO(e-) + RuIII-OH + H+→ RuII-OH2) occurred with smaller rate constants. Plots of the rate constants versus -Δ Go provided a reorganization energy of λPCET = 0.9 eV and λET = 0.5 eV. A second water oxidation catalyst provided similar values and demonstrated generality. The utilization of conductive oxides is shown to be a powerful tool for quantifying PCET reorganization energies at oxide surfaces for the first time.

RNA Polymerase: Step-by-Step Kinetics and Mechanism of Transcription Initiation.

To determine the step-by-step kinetics and mechanism of transcription initiation and escape by E. coli RNA polymerase from the λPR promoter, we quantify the accumulation and decay of transient short RNA intermediates on the pathway to promoter escape and full-length (FL) RNA synthesis over a wide range of NTP concentrations by rapid-quench mixing and phosphorimager analysis of gel separations. Experiments are performed at 19 °C, where almost all short RNAs detected are intermediates in FL-RNA synthesis by productive complexes or end-products in nonproductive (stalled) initiation complexes and not from abortive initiation. Analysis of productive-initiation kinetic data yields composite second-order rate constants for all steps of NTP binding and hybrid extension up to the escape point (11-mer). The largest of these rate constants is for incorporation of UTP into the dinucleotide pppApU in a step which does not involve DNA opening or translocation. Subsequent steps, each of which begins with reversible translocation and DNA opening, are slower with rate constants that vary more than 10-fold, interpreted as effects of translocation stress on the translocation equilibrium constant. Rate constants for synthesis of 4- and 5-mer, 7-mer to 9-mer, and 11-mer are particularly small, indicating that RNAP-promoter interactions are disrupted in these steps. These reductions in rate constants are consistent with the previously determined ∼9 kcal cost of escape from λPR. Structural modeling and previous results indicate that the three groups of small rate constants correspond to sequential disruption of in-cleft, -10, and -35 interactions. Parallels to escape by T7 RNAP are discussed.

A density functional theory study of the free‐radical scavenging activity of aminoguanidine. Comparison with its reactive carbonyl compound and metal scavenging activities

AbstractSince protein glycation is related to several human diseases, it is very important to develop molecules that can inhibit its effects. This work adds the reaction of Aminoguanidine (AG) with the methoxy (˙OCH3) and hydroperoxyl (˙OOH) radicals at the UM05‐2X‐SMD/6‐311+G(d,p) level of theory in water and pentyl ethanoate to simulate the physiological aqueous and lipidic environments. At physiological pH, AG is an effective ˙OCH3 and a moderate ˙OOH scavenger in nonpolar solvents (where AG is predominantly neutral), acting exclusively by hydrogen‐atom transfer. However, reactions in a polar solvent (where AG is predominantly cationic) have smaller rate constants. Therefore, the ability of AG to scavenge free radicals seems to depend on the polarity of the environment. Taken together, the results reported herein and in previous works suggest that the scavenging of reactive carbonyl species is the main mechanism of action of aminoguanidine in the context of protein glycation inhibition.

Understanding propyl cyanide and its isomers formation: ab initio study of the spectroscopy and reaction mechanisms.

Recent detection of propyl cyanide (C3H7CN) with both linear and branched structures has stimulated many experimental and theoretical studies. In this theoretical work, we present the spectroscopic properties of the far infrared spectra of these species and we investigate their different paths of formation in the gas phase. Our spectroscopic study concerns the far infrared spectra of iso, anti and gauche propyl cyanide isomers. The equilibrium structures and the potential energy surfaces are calculated using explicitly correlated cluster ab initio methods (CCSD(T)-F12) and a variational procedure designed for non-rigid species and large amplitude motions. Accurate rotational constants, centrifugal distortion constants, potential energy barriers and surfaces are provided. The rovibrational parameters in the ground vibrational states compare very well with experimental data. The low energy vibrational levels correspond to torsional modes. Far infrared energies are calculated up to 500 cm-1 using the variational approach and the vibrational second order theory (VPT2), and a good agreement with previous experimental values is found. We have also investigated the gas phase formation of the different C3H7CN isomers. After several trials of reacting gaseous species, we considered that a possible formation route of the C3H7CN isomers can be from the bimolecular reaction of HCN with propene. At the UMP2(full)/aug-cc-pVTZ level of theory, this reaction involves two steps for each isomer; the first one corresponds to the association of the two radicals while the second one corresponds to H transfer. From highly correlated ab initio calculations by means of CCSD(T)/aug-cc-pVTZ//UMP2(full)/aug-cc-pVTZ, the geometries, energetics and minimum energy paths of the reactions are obtained. Also, the first step's transition state disappears, as the diradical minimum is much less stabilized with UCCSD(T) than by UMP2(full). We employ the zero curvature tunneling and canonical variational (CVT/ZCT) semiclassical method to predict rate constants for propyl cyanide isomers formation in the gas phase. However, due to the presence of a significant barrier, this reaction leads to very small rate constants. Very recently, we probed reaction mechanisms involving radical addition and we found that these reactions are barrierless and highly exothermic leading to expected fast reactive processes for the formation of propyl cyanide products. The kinetics of such diradical reactions is under study.

Thermal inactivation kinetics of microencapsulated microbial transglutaminase by ultrasonic spray-freeze drying

Partially purified microbial transglutaminase (mTG) was microencapsulated by ultrasonic spray-freeze drying (USFD) as a novel method, using a 48 kHz ultrasonic nozzle. The microencapsulated samples, which used a mixture of inulin and gum arabic as coating materials, were compared to microencapsulated samples by conventional freeze-drying (CFD) and conventional spray drying (CSD) in terms of thermal stability. Thermal inactivation kinetics of the microencapsulated and as well as crude enzymes obtained by USFD process (USFD-crude) were evaluated according to first-order reaction kinetics in the range of 40–60 °C at different pH values (5.0–7.0), and the activation energy (Ea, kJ/mol) and free energy for thermal inactivation (ΔG, kJ/mol) were calculated. Furthermore, the specific surface area (SSA, m2/g) of the samples was determined, and a relationship between SSA and thermal stability was established. The results showed that the thermal stability of microencapsulated mTG by USFD was higher than all samples, having smaller rate constants and Ea values with higher half-life times and ΔG values. In addition, the thermal stability of the samples decreased when the SSA increased, as in USFD-crude and CSD samples.

Influence of restricted rotation of small-sized substituent on phosphorescence efficiency for Pt(II) complexes: A theoretical investigation

Abstract Herein, the radiative and non-radiative decay processes of six carborane-based Pt(II) complexes were explored with the help of the density functional theory and time-dependent density functional theory. In order to interpret the influence of non-metal heavy atoms on the phosphorescent quantum yields, the determined factors, i.e., the ZFS (zero-point filed splitting) parameters, radiative decay rate constants and photodeactivation mechanisms, were unveiled. The results indicate that the spin-orbital coupling effects can be slightly regulated via introducing the non-metal heavy atoms into the carborane. Also, the non-metal heavy atoms substituents could cause slightly decrease of the energy barriers between the 3ES and 3MC excited states, and thus, for Pt-6, a fast non-radiative decay process may occur. Moreover, compared with the Pt-1, the rotation of methyl in Pt-2 ∼ 5, can be effectively restricted with the aid of hydrogen bonding and halogen bonding, which is beneficial for obtaining small non-radiative decay rate constants. Accordingly, it provides a strategy for realizing the restriction of small group rotation to achieve the high-efficient phosphorescent emitters.

Excited state intersystem crossing and the relaxation dynamics of phosphorescent Ir(III) complexes bearing bipyridine-based C^N ligand

Abstract The photo-deactivation mechanism of heteroleptic Ir(III)(C^N)2 (LX) complexes [(dfpypy)2Ir(pic)](1) and [(dfppy)2Ir(pic)](2) [where dfpypy = 2′,6′-difluoro-2,3′-bipyridine, dfppy = 2-(2,4-difluorophenyl)pyridine, pic = 2-picolinate] were elucidated by density functional theory/time-dependent density functional theory (DFT/TD-DFT) to rationalize the nature of the significant differences in luminescence efficiency between 1 and 2. Specifically, the radiative deactivation was formulated through the calculation of zero-field splitting (ZFS) and the radiative decay rate constant (kr) based on spin-orbit coupling (SOC). Meanwhile, the non-radiative deactivation was estimated by considering the structural distortion, the SOC between the emitting state and the ground state, as well as the thermal deactivation process via metal-centered excited 3MC state. Based on the results, 1 has much smaller SOC matrix elements between T1 and S0 than 2, which determines its small non-radiative decay rate constant, thus one may understand why 1 has higher phosphorescence quantum efficiency than 2. To further explore the structure-property relationship of Ir(III) complexes, four other new complexes 3–6 were designed by incorporating trimethylphenyl(R1), phenyl(R2), ter-butyl (R3), diphenylamine(R4) to the pyridine rings of dfpypy ligand of 1, respectively. Through analyzing, complex 4 with larger radiative decay rate and smaller non-radiative decay rate may be considered as a potential candidate as robust blue-emitting material applied in organic light emitting diodes (OLEDs).