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The electronic structures and photophysical properties of Ir(tpy)2(acac) complex (1) and the derivative (2, 3) with thiophene at different positions of tpy ligands have been investigated with density functional theory (DFT) and time-dependent density functional theory (TD-DFT), where tpy = 2,2-thienylpyridine, acac = acetylacetonate. 3a and 3b are studied to get insight into the influence of different positions of fluorine atoms on the photophysical properties of 3. The calculated results reveal that the introduction of thiophene are beneficial to enhance absorption intensity, decrease LUMO energy levels, and reduce the energy barrier for electron injection compared with 1. However, the decreased amount of metal orbitals involved in the transitions, small participation of metal to ligand charge transfer contribution in both the absorption (MLCT%) and emission spectra (3MLCT%), large energy difference between the S1 and Tm (ΔES1−Tm) for 2 (m = 1–2) and 3 (m = 1–3) compared with those of 1 account for their relatively low phosphorescence quantum yields (Φp) observed experimentally. Moreover, the incorporation of F atoms into complex 3 (3a, 3b) can be efficient approach of tuning the electron injection ability, balance of charge transfer process, and emitting color. Especially, the high quantum yield of 3b compared with 3a is explained based on the detailed analysis of the triplet energy (ET1), transition dipole moment (μS1) upon the S0 → S1, SOC matrix element between the Tm and Sn states, ΔES1−Tm, 3MLCT% in the phosphorescent spectra, energy difference between 3MLCT and electronic configurations of the triplet metal-centered (3MC) d–d excited states. These structure-property relationship is expected to provide useful information for synthesis highly efficiency phosphorescence emitters.

Theoretical investigation on a series of Pt(Ⅱ) complexes to evaluate the influence of diphenylamine group on the optical properties and their potential applications in PhOLEDs. The effect of different substituent positions (1a-1c) on the electronic structures and optical properties were fully explored by compared with the experimental synthesized complex 1. The functionalized diphenylamine moiety can tune the geometrical structures, frontier molecular orbitals, absorption and emission spectra, radative rate (kr), possbile nonradative process T1(3MLCT/π → π*) → TS(d-d)→3MC(d-d) → MECP(d-d), charge injection and transfer properties. The findings could help to understand the influnece of dipenylamine group and design high efficient red guest emitters in PhOLEDs.

Quantum-chemistry methods are used to investigate the effect of phenylamine chromophore on the electronic structure, optical properties, and phosphorescence efficiencies of a series of fac -iridium(III) complexes, Ir-(g0) 3 (1) , meta-substituted Ir compounds [Ir-(g0) 2 -(g1) 1 ] (1a) , [Ir-(g0) 1 -(g1) 2 ] (1b) , [Ir-(g1) 3 ] (1c) and para-substituted Ir compounds [Ir-(g0) 2 -(g1′) 1 ] (2a) , [Ir-(g0) 1 -(g1′) 2 ] (2b) , [Ir-(g1′) 3 ] (2c) , where g0 = l -phenylisoquinolinato, g1 = 4-(isoquinolin-1-yl)- N , N -diphenylbenzenamine, g1′ = 3-(isoquinolin-1-yl)- N , N -diphenylbenzenamine. The calculations show that introduction of phenylamine chromophore at meta position of phenyl ring ( 1a – 1c ) slightly changes the ground-states geometries but largely increases the energy of HOMO and decreases IP values hence improves the ability of hole injection, which is consistent with the experimental report. The introduction of diphenylamine substitutions on the para position ( 2a – 2c ) is effective for extending the π-electron delocalization, which results in strengthening metal-ligand bond and dramatically increasing the HOMO energy. More important, the 2a – 2c have enhanced metal-to-ligand charge transfer 3 MLCT participation in the phosphorescent spectra, decreased the singlet-triplet splitting energy (Δ E S1–T1 ), as well as dramatically small energy differences between the highest occupied orbitals splitting (Δdd occ ) and large lowest unoccupied d-orbitals splitting (Δdd*) at the both S 0 and T 1 geometries, these account for the quantum yield and efficiency of phosphorescence. The calculated ionization potentials (IPs), electronic affinities (EAs), and reorganization energy ( λ ) confirm that the hole and electron injection and transfer ability were enhanced by importing the diphenylamine. Furthermore, based on the analyses of triple energy differences between host and guest, charge carrier mobility, optical overlap, it is found that these Ir complexes maybe good guest materials in CBP. Thus, the introduction of phenylamine at para position is effective approach to obtain highly efficient red phosphorescent emitters.

The electronic structures and photophysical properties of a series of Ir(III) complexes, Ir(C^C)(ppy)2, Ir(C^C)(ppy)(OrtCF3), Ir(C^C)(ppy)(MeCF3) and Ir(C^C)(ppy)(ParCF3), where ppy=2-phenylpyridine, C^C=1-(2,4-difluorophenyl)-1H-imidazole, OrtCF3=2-(2-(trifluoromethyl)phenyl)pyridine, MeCF3=2-(3-(trifluoromethyl)phenyl)-pyridine, and ParCF3=2-(4-(trifluoromethyl)phenyl)pyridine, were investigated by density functional theory calculation employing the mPW1PW91 density functional. The simulated electronic structure, absorption spectra, and phosphorescence of Ir(C^C)(ppy)2 were in good agreement with the experimental values. Compared with Ir(C^C)(ppy)2, it was found that introduction of the CF3 substituent on the ortho -and para -position of ppy was more useful to strength the metal-ligand bond, enhance the electron injection ability, as well as red-shifted the absorption spectra and phosphorescence. Furthermore, Ir(C^C)(ppy)(OrtCF3) had increased participation of triplet metal to ligand charge transfer (3MLCT) contributions, large transition dipole moment ( m S1) and d orbital splitting, small singlet-triplet splitting energy (D E S1-T1) compared with other complexes, which indicated Ir(C^C)(ppy)(OrtCF3) would be potential phosphorescence emitters with high quantum yield.

The electronic structures and photophysical properties of a series of blue-emitting Ir(Ⅲ) complexes, Ir(ppy) 2 (C ∧ C)]( 1′ ), Ir(ppy) 2 (CF ∧ C)]( 1 ), [Ir(ppy) (MeFPP) (CF ∧ C)]( 2 ), [Ir(MeFPP) 2 CF ∧ C)]( 3 ), [Ir(ppy) (PaOrFPP) (CF ∧ C)]( 4 ), [Ir(PaOrFPP) 2 (CF ∧ C)]( 5 ), where C ∧ C = 2,3-dihydro-1-methyl-3-phenyl-1H-imidazole, CF ∧ C = 1-(2,4-difluorophenyl)-2,3-dihydro-3-methyl-1H-imidazole, ppy = 2-phenyl- pyridine, MeFPP = 2-(3,5-difluorophenyl)pyridine and PaOrFPP = 2-(2,4-difluorophenyl)pyridine, were investigated by density functional theory and time-dependent density functional theory calculations employing the mPW1PW91 density functional. The simulated electronic structure, absorption spectra, and phosphorescent of complex 1′ and 1 were in good agreement with the experimental values. The calculated energy values of HOMO, LUMO, ionization potential (IP), electron affinity (EA), and reorganization energy (λ) showed that the abilities of electron injection and transport were dramatically improved by introducing electron-withdrawing fluorine atoms. Additionally, those Ir complexes containing fluorine atoms strengthened the metal-ligand bond and increased the participation of MLCT contribution in absorption spectra compared with 1 ′ and thus further improved the collection of light energy participation from metals. Furthermore, the detailed analysis of participation of 3 MLCT contributions, E T1 , ΔE S1-T1 , d-orbital splitting revealed that the quantum yield was effectively enhanced both by introducing the fluorine atoms at 2,4-position of phenyl on the ppy ligand and by increasing the number of fluorine atoms. We hope this work is useful to gain the structure-property relationship and provide valuable information for designing highly blue phosphorescent materials for organic light-emitting diodes (OLEDs).

To design efficient organic sensitizer, a series of D-π-A indoline dyes with different donor parts have been investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT) approach. The molecular geometries, frontier molecular orbitals, and absorption spectra of these dyes have been systematically investigated to provide comprehensive understanding of the structure-property relationships. Compared with D149, our designed dyes have proper HOMO and LUMO energy level, narrowed HOMO-LUMO energy gap, and broadened absorption band by introducing the N(CH3)2and N(phenyl)2groups at the donor part. Furthermore, the dimeric dyes and dye-(TiO2)6systems have been optimized by DFT method to simulate the intermolecular interactions, as well as interaction between the dyes dimmers and semiconductor interface, respectively. Through the analyses of absorption energies (Eads), energy levels of the HOMO and LUMO, light harvesting efficiency (LHE), and the driving force of electrons injections (ΔGinject), it is found that the designed dyes should have improved optical properties by importing the N(CH3)2group. This work is hoped to provide a theoretical guiding role in design of new dyes for dye-sensitized solar cells.

As a key factor for promoting electron transfer to the semiconductor, the intramolecular charge transfer (ICT) process in dye-sensitized solar cells (DSSCs) is crucial to enhancing the conversion efficiency. In this study, the effects of anchoring groups on charge transfer during dye excitation and interfacial electron injection from the dyes to the semiconductor were theoretically investigated. The calculation results indicate that the sensitizers with hydantoin anchoring groups, namely HY-4, HY-3, HQ-4, and HQ-3, can significantly adjust the orbital energy levels and increase the HOMO-LUMO energy gaps. Importantly, the ICT process of sensitizers before and after binding TiO2 cluster were detected via frontier molecular orbitals, electronic transition processes and transferred charges on the basis of the excitation (qCT), the transferred charge distance (dCT) and the dipole moment (μCT). The calculation results confirm that HY-4 and HY-3 greatly improve ICT performances relative to CA-4, which successfully interprets the experimentally observed efficiency difference. Moreover, the inserting acceptor moiety quinoxaline and hydantoin anchoring groups, namely HQ-4 and HQ-3, play an important role in raising the efficiency of ICT process. The finding can promote further understanding of the relationship between structure and performance of organic dyes containing hydantoin anchoring groups, so as to help them become more efficient dyes for DSSCs.

The stepwise hydrogenation of the C=C bond and C=O group of acrolein on Au3 and Au5 model systems is investigated using the density functional theory(DFT) PW91 functional. Our results show that the C=C hydrogenation is more favorable than that of C=O bond on Au3 with the barriers of the rate-determining step being 0.35 and 0.62 eV respectively. On the other hand, the C=O reduction is preferred over the hydrogenation of the C=C bond on Au5. The corresponding barriers of the rate-determining steps are 0.45 and 0.54 eV, respectively. This demonstrated that the second hydrogenation step controls the reaction on both Au3 and Au5 for C=O and C=C hydrogenation and the C=O hydrogenation on Au5 is preferred over the hydrogenation of the C=C bond, which is helpful to address the reactivity of small size-selected supported gold clusters.

A density functional theory and time-dependent density functional theory approaches were used to understand the structure–property relationships of a series of Ir(III) complexes Ir(x-NHC)(y-ppy)2 [where NHC = 2,3-dihydro-1-methyl-3-phenyl-1H-imidazole, ppy = 2-phenylpyridine, x = Cl, y = H (1a); x = Cl, y = Cl (1a-Cl); x = Cl, y = F (1a-F); x = Cl, y = CN (1a-CN); x = Cl, y = CF3 (1a-CF 3 ); x = F, y = CF3 (2-CF 3 )]. The investigations on the electronic structures in the ground and lowest triplet excited states, the frontier molecular orbitals, the absorption and emission spectra, as well as charge injection and transport of these Ir complexes provided a good understanding of the structure–property relationships. Furthermore, the full details of the metal character in the phosphorescent spectra(3MLCT %), triplet energy (E T1), the singlet–triplet splitting energy (ΔE S1–Tn), 3MLCT–3MC energy gap, as well as d orbitals splitting revealed that quantum yield was effectively enhanced by introducing CN and CF3 groups on the ppy ligands. The designed complexes 1-CN, 1-CF 3 , and 2-CF 3 are expected to be highly efficient phosphorescent materials in organic light-emitting diodes.

A new series of triphenylamine-based indoline dye sensitizers were molecularly designed and investigated for their potential use in dye-sensitized solar cells (DSSCs). Theoretical calculations revealed that modifying donor part of D149 by triphenylamine significantly altered the electronic structures, MO energies, and intramolecular charge transfer (ICT) absorption band. Key parameters associated with the light-harvesting efficiency at a given wavelength LHE(λ), the driving force ΔG inject, and the open-circuit photovoltage V oc were characterized. More importantly, these designed (dimeric) dye sensitizers were found to have similar broad absorption spectra to their corresponding monomers, indicating that modifying the donor part with triphenylamine may stop unfavorable dye aggregation. Further analyses of the dye-(TiO2)9 cluster interaction confirmed that there was strong electronic coupling at the interface. These results are expected to provide useful guidance in the molecular design of new highly efficient metal-free organic dyes.

The geometrical structures and photophysical properties of Ir(4,6-dFppy)2(pic) (FIrpic) and its derivative (o-FIr, m-FIr, p-FIr) with dimethylamine substituted at the picolinic acid (N∧O) ligand were fully investigated by density functional theory and time-dependent density functional theory. The simulated electronic structure, as well as absorption and emission spectra of FIrpic are in good agreement with the experimental observations. The introduction of dimethylamine at the N∧O ligand at different positions is beneficial to extend the π-electron delocalization, increase HOMO energy levels, and hence improve the hole injection and transfer ability compared with those of FIrpic. Furthermore, o-FIr, m-FIr, and p-FIr have large absorption intensity and participation of metal-to-ligand charge transfer (MLCT) contribution in the main absorption spectra, which would be useful to improve the intersystem crossing (ISC) from the singlet to triplet excited state. More importantly, the high quantum yield of o-FIr (which is explained based on the detailed analysis of triplet energy, ET1), participation of 3MLCT contribution in the phosphorescent spectra, and energy difference between 3MLCT and triplet metal centered (3MC) d-d excited state compared with m-FIr and p-FIr indicate that o-FIr is expected to be an excellent blue phosphorescence emitter with high efficiency.