Theoretical studies on the hole transport property of tetrathienoarene derivatives: The influence of the position of sulfur atom,substituent and π-conjugated core

Chemical modifications such as changing the position of heteroatom, introducing different substituents and π-conjugated cores are powerful molecular design tools to modulate their optical and electrochemical performance. In this context, in-depth density functional theory investigations on the geometries, frontier molecular orbitals, reorganization energies, transfer integrals, anisotropic mobilities and band structures of tetrathienoarene derivatives were carried out to provide insights into the effects of these chemical modifications on their hole transport properties. The electrostatic potential, Hirshfeld surface analysis, energy decomposition analysis (EDA) and anisotropic mobility were also employed to shed light on the intricate interplays among molecular packings, intermolecular interactions and transport properties. It is found that compared with 2, 1a with sulfur atom inside has lower frontier orbital energy level, smaller reorganization energy and larger transfer integral and hole mobility. However, more S⋯S interactions in 2 could provide more effective transport channels for charge carrier transport. The introduction of hexylthienyl groups (1c) results in an enhancement of π–π interaction and leads to an increase in the highest occupied molecular orbital (HOMO) and transfer integrals. Meanwhile, the strongest intermolecular interaction energy of pathway A in 1c renders its transport behavior with typical one-dimensional (1D) transport. Moreover, anthracene as the π-conjugated core seemed to possess better transport properties in comparison with dibenzothiophene or chrysene acting as core. In addition, the dispersion energy of all investigated compounds plays a leading role in determining the energetically accessible stacking motifs. We hope that our speculation would facilitate the future design and preparation of high-performance charge-transport materials.     

Unveiling photophysical properties of phenanthro[9,10-d]imidazole derivatives for organic light-emitting diodes

Recently, two phenanthro[9,10-d]imidazole derivatives exhibited excellent advantages in organic light-emitting devices (i.e. high luminous efficiency, high carrier mobility, and low turn-on voltage). However, the relationship between their photophysical properties and the structural characters or intermolecular interactions remain elusive, which is considerable importance to further performance improvement. Currently, density functional theory (DFT) and time-dependent DFT (TD-DFT) have become powerful tools to rationalize photophysical properties and to design new materials with improvement performance. The simulated electron absorption and emission wavelengths of compounds 1 and 2 are in good agreement with the experimental ones. For the studied compounds, the involvement of tert-butyl moiety has negligible effect on energy level and distribution of frontier molecular orbitals (FMOs), whereas greatly affects electron transition of deep energy level and charge transport property. Synergy of π-π and CH···π intermolecular interactions is responsible for the bipolar carrier transport, while CH···π for hole transport. The incorporation of NH₂ on phenanthro[9,10-d]imidazole and NO₂ on diphenylamino part is an effective way to tune FMOs energy level and intramolecular charge transfer, leading to the substantial enhancement of the second-order nonlinear optical (NLO) response. Our work is also important for understanding photophysical properties and designing photoelectric materials of phenanthro[9,10-d]imidazole derivatives.     

The substituent effect on charge transport property of triisopropylsilylethynyl anthracene derivatives

The charge transport property of two triisopropylsilylethynyl anthracene (TIPSAnt) derivatives TIPSAntBt and TIPSAntNa (bithiophene and naphthalene are introduced at the 2, 6-positions of the TIPSAnt core) were explored through quantum chemical method. To gain a better understanding of the substituent effect on the charge transport property, the results of the parent molecule TIPSAnt was also provided here for comparison. The substituent effect on the molecular geometry, reorganization energy, frontier orbitals, ionization potential (IP) and electronic affinity (EA), crystal property, transfer integrals and charge mobility, band structure and effective mass of the two compounds were investigated to establish the relationship between structures and properties. The introduced bulky TIPS groups made the two compounds adopt two-dimensional, face-to-face, π-stacking structures. The efficient overlaps of π-orbital and smaller π-stacking distance are proved to be the main reason for the high charge mobility of TIPSAntBt and TIPSAntNa. The hole mobilities of TIPSAntBt and TIPSAntNa are 0.88 and 3.60 cm² V⁻¹ s⁻¹, respectively, which is well consistent with experiment values (0.2 and 3.7 cm² V⁻¹ s⁻¹, respectively). For TIPSAntBt, the electron mobility (1.29 cm² V⁻¹ s⁻¹) is a little higher than that of hole due to the more effective transfer integrals of electron. On the contrary, the hole mobility of TIPSAntNa is 20 times larger than that of electron because of the smaller reorganization energy and larger transfer integral of hole, indicating that TIPSAntNa could be used as p-type semiconductor. For TIPSAntBt, the transfer integral is smaller than the reorganization energy, so the hopping mechanism plays a key role in the charge transport property. While the bandwidths and effective mass of TIPSAntNa agreed well with the calculated transfer integrals and charge mobility results. The introduced small substituents to TIPSAnt core contributed to the dramatically different charge transport property from an n-type semiconductor of TIPSAntBt to p-type semiconductor of TIPSAntNa, which shed light on molecular design for an n-type semiconductor through simple chemical structural modification.     

High-performance room-temperature NO2 sensors based on microstructures self-assembled from n-type phthalocyanines: Effect of fluorine–hydrogen bonding and metal–ligand coordination on morphology and sensing performance

To investigate the effect of fluorine–hydrogen bonding and metal–ligand coordination on the morphology and gas sensing properties of self-assembled nanostructures, metal free 2,3,9,10,16,17,24,25-octakis(heptafluorobutoxy)phthalocyanine H₂[Pc(OCH₂C₃F₇)₈] (1) and its zinc complex counterpart Zn[Pc(OCH₂C₃F₇)₈] (2) are synthesized and fabricated into organic microstructures by a phase-transfer method. The self-assembling properties have been comparatively investigated by electronic absorption and Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and current–voltage (I–V) measurements. Competition and cooperation between the inter-molecular π-π interaction and C-H⋯F-C hydrogen bonding in the direction perpendicular to the π-π interaction direction for metal-free phthalocyanine 1 lead to the formation of uniformed two-dimensional helical microribbons with an aspect ratio (length/width) of ca 20. The additional Zn-O coordination interactions between the central zinc ion and the oxygen atom of the adjacent molecule increases the intermolecular interaction, and results in the formation of long one-dimensional nanowires for 2 with an aspect ratio of more than 200. Notably, the resulting microstructures were revealed to show good semiconducting properties with the increasing conductivity from 5.99 × 10⁻⁵ S cm⁻¹ for the nanowires of 2 to 1.68 × 10⁻⁴ S cm⁻¹ for the helical ribbons of 1. Moreover, the excellently sensitive, stable and reproducible responses to NO₂ in 50–900 ppb range are observed for the helical ribbons of 1 at room temperature, implying the excellent potential as the NO₂ sensor for applications in practical environments. Both sensitivity and detection limit of the helical ribbons of 1 for NO₂ gas at room temperature was found to be better than those of the nanowires of 2. This suggests that the analyte-phthalocyanine interaction is dominated by not only high conductivity and great surface area but more importantly binding strength of analyte to the central cavity of the phthalocyanine.     

Merocyanines for vacuum-deposited small-molecule organic solar cells

We report here synthesis and photovoltaic properties of three merocyanines dyes (DPPT, DTPT, 1-NPPT) which are functionalized with electron withdrawing thiazolidenemalononitrile and electron rich diarylamine functionalities. It is found that structural feature of the diarylamino groups has a profound effect on the physical properties such as the absorption spectrum, oxidation potential, and HOMO/LUMO energy levels. The compound DTPT containing a better electron-donating ditolyl group, exhibits red-shifted absorption with relatively higher molar extinction coefficient, indicating its better light-harvesting ability. Hole mobility of these compounds is found to be strongly dependent on the various intermolecular interactions. Interestingly, single crystal structures reveal that the crystal packing motifs are rather closely related to the observed hole mobility in a trend of DPPT > DTPT > 1-NPPT. Vacuum-processed small-molecule organic solar cells were fabricated using the title merocyanines as p-type materials (donor) in combination with fullerene (C₆₀ or C₇₀) as n-type material (acceptor) with various device configurations. Among them, the DPPT-based devices outperform the devices based on DTPT and 1-NPPT. The power conversion efficiency (PCE) of DPPT-based device was improved from 1.55% of a BHJ device to 2.63% of a PMHJ device and 3.52% of a PMHJ device without the thin donor layer.     

Theoretical study on charge transport properties of cyanovinyl-substituted oligothiophenes

When the oligothiophene is substituted by dicyanovinyl (DCV) or tricyanovinyl (TCV) group, how does its transport property change? Here, we will mainly focus on exploring the influence on charge transport properties of introducing a strong electron-withdrawing DCV/TCV group to the thiophene units within Marcus–Levich–Jortner formalism at the level of density functional theory. The results show that the introduction of cyanovinyl-substituents improves the molecular π-stacking, decreases the frontier molecular orbital energy levels and reorganization energies, and increases the transfer integrals and mobilities, comparing with their parent thiophene molecules. It is interesting to find the phenomenon that enriching intermolecular interactions can be favorable for controlling the transport channel and thus get high mobility, which would be shown by the angular resolution anisotropic mobilities analysis. Besides, the simulated packing motifs of dimers for 3a and 3b without crystal structures reported indicate that their packing may form the slip π–π stacking, and that 3b may be a good ambipolar material. In a word, compared with corresponding thiophene analogues and tetracyanoquinodimethane, these compounds may become the candidates for the n-type or ambipolar organic semiconductor materials.     

A highly emissive distyrylthieno[3,2-b]thiophene based red luminescent organic single crystal: Aggregation induced emission,optical waveguide edge emission,and balanced ambipolar carrier transport

A highly emissive red luminescent single crystal which shows aggregation induced emission (AIE) property and optical waveguide edge emission based on small organic functional molecule, cyano-substituted 2,5-di((E)-styryl)thieno[3,2-b]thiophene (CNP2V2TT) has been prepared by the physical vapor transport (PVT) method. The fluorescence quantum efficiency of crystal is up to 37% and an emission peak maximum (λ_max) locates at 645 nm. Cystallographic data indicate that uniaxially oriented molecular packing with slipped face-to-face π-π stacking forms by the hydrogen bonding network among CNP2V2TT molecules. The single crystal FET devices were fabricated using Au and Ca as hole and electron injection electrodes, respectively. The molecular design, introducing cyano groups into molecular skeleton, effectively lower the LUMO level and achieve well-balanced ambipolar electron (0.13 cm² V⁻¹ s⁻¹) and hole (0.085 cm² V⁻¹ s⁻¹) mobilities.     

Donor–acceptor–acceptor–donor small molecules for solution processed bulk heterojunction solar cells

We report on the optical and electrochemical characterization (experimental and theoretical) of two donor substituted benzothiadiazole with different cyano based acceptor π-linkers, tetracyanobutadiene (TCBD) SM1 and dicyanoquinomethane (DCNQ) SM2, and explore them as the donor component for solution processed bulk heterojunction organic solar cells, along with PC₇₁BM as the electron acceptor. The solution bulk heterojunction (BHJ) solar cells based on dichloromethane (DCM) processed active layer with SM1 and SM2 as donor and PC₇₁BM as acceptor achieve power conversion efficiency (PCE) of 2.76% and 3.61%, respectively. The solar cells based on these two small molecules exhibit good Voc, which is attributed to their deep HOMO energy level. The higher PCE of the device based on SM2 compared to SM1 is attributed to the its small bandgap, broader absorption profile and enhanced hole mobility. Additionally, the PCE of the SM2:PC₇₁BM based solar cells processed with 1-chloronaphthalene CN (3 v%)/DCM is further improved reaching upto 4.86%. This increase in PCE has been attributed to the improved nanoscale morphology and more balanced charge transport in the device, due to the solvent additive.     

A dπ-pπ Conjugated System with High Mobility and Strong Emission Simultaneously

Strong intermolecular interactions usually facilitate charge transport, but impede photoluminescence, therefore, the development of organic π-conjugated materials that exhibit both semiconducting and light-emissive properties remains challenging. Herein, a series of perylene diimide (PDI)-based carbolong complexes with d_π-p_π conjugation is synthesized. The resulting alcohol-soluble products exhibit broad and strong absorption combined with outstanding electronic and optical properties, and are applied as electron transport layer materials in organic solar cells, achieving power conversion efficiencies up to 17.36%. In addition, these complexes exhibit an uncommon aggregation-induced emission phenomenon. These results will aid in future design of π-conjugated materials with increased functionality.     

New soluble porphyrin bearing a pyridinylethynyl group as donor for bulk heterojunction solar cells

Bulk heterojunction solar cells were fabricated using the blend films of a porphyrin bearing pyridinylethynyl group (POR) as electron donor and PC₆₀BM or PC₇₀BM as electron acceptor. Photoluminescence measurement of the blend films of POR with fullerene derivatives indicated that charge transfer was possible between POR and fullerene derivatives. The solution processed bulk heterojunction solar cells using the blend of POR with PC₆₀BM and PC₇₀BM exhibit overall power conversion efficiency (PCE) of 1.96% and 2.54%, respectively. The PCE of the BHJ solar cell has been further improved up to 3.27% when thermally annealed POR:PC₇₀BM was used as active layer, which is attributed mainly to the increase in short circuit current. The increase in J_sc is attributed to the enhanced crystallinity of the blend (particularly POR) and efficient π-electron conjugation of POR, resulting to an improvement in hole mobility, leading to more balance charge transport. The PCE of the device based on as cast POR:PC₇₀BM has been further improved up to 4.06% when DMF treated PEDOT:PSS buffer layer was used.     

Effect of linker used in D–A–π–A metal free dyes with different π-spacers for dye sensitized solar cells

Two novel D–A–π–A metal free dyes with triphenylamine as donor, dithiophene-diketo-pyrrolo-pyrrole as acceptor unit, thiophene and phenyl π-conjugated bridges and a cyanoacetic acid as electron acceptor (TDPP1 and TDPP2 were denoted for thiophene and phenyl π-conjugated bridge, respectively) have been designed and used as sensitizers for DSSCs. Incorporation of dithiophene-diketo-pyrrolo-pyrrole, reduces the band gap significantly. The influence of π-conjugated bridge on optical and electrochemical properties were investigated. Results demonstrated that the absorption band of TDPP with thiophene π-conjugated bridge has red shifted due to the enhancement of electron donating ability of π-conjugated bridge. The DSSC based on TDPP1 shows prominent power conversion efficiency about 4.81%, which is higher that for TDPP2 (3.42%). The electrochemical impedance spectroscopy analysis reveal that the charge recombination resistance at the TiO₂/dye/electrolyte interface for the DSSC based on TDPP1 is higher than that for TDPP2, which improves both J_sc and V_oc. The PCE of the DSSC based on TDPP1 is further improved up to 6.34%, when deoxycholic acid (DCA) was employed as coadsorbant.     

Hydrogen bond directed assembly of oligothiophene/fullerene superstructures on Au(1 1 1)

We previously reported that a branched quaterthiophene donor chromophore functionalized with a phthalhydrazide hydrogen bonding (H-bonding) unit (MeBQPH) gives twofold more efficient bulk heterojunction organic solar cells (with C₆₀ acceptors) compared to a nearly identical donor incapable of H-bonding (MeBQPME). Here, scanning tunneling microscopy (STM) studies confirm the formation of MeBQPH trimer rosettes on Au(1 1 1) through phthalhydrazide H-bonding interactions that are sufficiently strong to compete with adsorbate/substrate interactions. The MeBQPME comparator molecule void of hydrogen bonding functionality does not similarly assemble on the metal surface. Complementary density functional theory (DFT) calculations facilitate a structural understanding of the MeBQPH donor assemblies and their strong stabilization through formation of six hydrogen bonds. STM studies also reveal the templated growth of C₆₀ on ordered MeBQPH monolayers with C₆₀ molecules preferentially occupying the threefold interstitial sites of the MeBQPH monolayer. This work supports the idea that H-bonding interactions can be used to control the morphology of organic donor–acceptor blends to potentially create efficient and stable bulk heterojunction photovoltaic devices.     

Thieno[2,3-b]indole-based organic dyes for dye-sensitized solar cells: Effect of π-linker on the performance of isolated dye and interface between dyes and TiO2

A series of novel D-π-A type organic dyes with different π-linker are theoretically designed and investigated for their potential applications in dye-sensitized solar cells (DSSCs). We mainly focused on the influence of the extension of π-linker on the overall efficiency. The discussions are classified into two aspects: one is the isolated dyes and the other is the dye-TiO₂ system. The calculated results indicate that the isolated dyes THI-2T-C, THI-4T-3C, and THI-6T-5C have the better overall efficiency. Further, the THI-4T-3C and THI-5T-4C have the acceptable performance if the dye-TiO₂ system is considered. Combination of the isolated and the adsorbed systems, the THI-4T-3C with the moderate π-linker is considered to be more suitable choice for thieno[2,3-b]indole-based dyes rather than the longest π-linker.     

Metal-free photosensitizers based on benzodithienothiophene as π-conjugated spacer for dye-sensitized solar cells

A novel series of metal-free organic photosensitizers based on D-π-A or D-A₁-π-A structure motif namely, BD-n, (where n = 1–5) bearing a high hole-transporting benzodithienothiophene as the π-bridge for the first time, carbazole or triarylamine as the electron-donor and benzothiadiazole or quinoxaline as the auxiliary electron-deficient unit was synthesized and investigated for DSSC applications. DSSCs based on these five photosensitizers were also fabricated which exhibited efficiencies ranging from 3.92% to 5.46%. Among these DSSCs, devices based on D-A₁-π-A type dye, BD-3 and bidenate dye, BD-5 as a photosensitizer afforded the best efficiencies of 5.34%–5.46%. Our results suggested that an incorporation of a proper auxiliary accepting group (A₁) into the D-π-A conjugation system to enhance light harvesting and charge transfer as well as the use of V-shaped di-anchoring strategy to suppress aggregation on the TiO₂ surface were found to be useful and effective strategies to enhance the photovoltaic performance of a DSSC. These devices exhibited relatively long electron lifetimes suggesting the slow charge recombination kinetics and thus better DSSC performance. Our findings also suggest that benzodithienothiophene is a promising π-bridge to construct organic photosensitizers for high-efficiency DSSCs.     

Characterization of two new (A–π)2–D–A type dyes with different central D unit and their application for dye sensitized solar cells

We report the photophysical, electrochemical and theoretical properties of two dyes with same acceptor, π-linker and anchoring acceptor unit and different TPA (D1) and pyran (D2) donor central unit. The change in the central unit resulted in corresponding different photophysical and electrochemical properties. The dye sensitized solar cell fabricated using dye D1 showed the higher incident photon to current efficiency of 54%, a short circuit current (J_sc) of 11.86 mA/cm², an open circuit voltage of 0.64 V, and fill factor (FF) of 0.68, corresponding an overall power conversion efficiency of 5.16% which is higher than that for D2 based DSSCs (4.42%). The difference in the PCE of DSSCs based on D1 and D2 is partly, due to the smaller amount of dye loading, higher dark current and charge recombination rate of D1 based DSSC. The electrochemical spectra of DSSCs demonstrated longer electron life time and charge recombination resistance and small charge transport resistance for D1 sensitized DSSC, results the higher PCE.     

Aza[5]helicene Rivals N‐Annulated Perylene as π‐Linker of D−π−D Typed Hole‐Transporters for Perovskite Solar Cells

The superior role of helical π‐linkers is demonstrated for the design of donor?π linker?donor typed molecular semiconductors in perovskite solar cells (PSCs). Flat N‐annulated perylene (NP) and contorted aza[5]helicene (A5H) are side‐functionalized with methoxyphenyl and end‐capped with dimethoxydiphenylamine electron‐donor to afford two small‐molecule hole‐transporters J3 and J4. For methoxyphenyl functionalized π‐linkers, intermolecular π???π interactions in planar NP exist more extensively than those in helical A5H. However, for the dimethoxydiphenylamine derived hole‐transporters with high highest occupied molecular orbital energy levels, a part of the π???π interaction remains for J4 with A5H, while this desirable effect for charge transport is completely deprived for J3 with NP. Thus, the theoretically predicted hole mobility of J4 single‐crystal is even over two times higher than that of J3 one. Because of the larger size of the molecular aggregate, the hole mobility of the spin‐coated J4 thin film is also over three times as high as that of the J3 analog. Due to the reduced transport resistance and enhanced recombination resistance, PSCs with J4 exhibit a power conversion efficiency of 21.0% at standard air mass 1.5 global conditions, which is higher than that of 19.4% with J3 and that of 20.3% with spiro‐OMeTAD control.     

Benzodithiophene-based small molecules with various termini as hole transporting materials in efficient planar perovskite solar cells

In this study we prepared four benzodithiophene (BDT)-based small organic molecules presenting bithiophene (TT), thiophene (FT), carbazole (CB), and triphenylamine (TPA) units, respectively, as termini, and used them as hole transporting materials for perovskite solar cells (PSCs). The high degrees of planarity of these BDT-based small molecules imparted them with high degrees of stacking and charge transport. These small molecules had suitable optical properties and energy level alignments for use in PSCs based on MAPbI₃, with compact-TiO₂ as the electron transporting layer and a BDT-based material as the hole transporting layer, in a n–i–p structure. Among our tested BDT-based materials, the PSC incorporating BDT-TT had the best performance, with an average power conversion efficiency of 13.63%.     

Triarylamine-based dual-function coadsorbents with extended π-conjugation aryl linkers for organic dye-sensitized solar cells

Triarylamine-based dual-function coadsorbents containing a carboxylic acid acceptor linked by extended π-conjugation aryl linkers (e.g., phenylene: HC-A3, naphthalene: HC-A4 and anthracene: HC-A5) were newly designed and synthesized. They were used as coadsorbents in organic dye-sensitized solar cells (DSSCs) based on a porphyrin dye (hexyloxy-biphenyl-ZnP-CN-COOH (HOP)). For comparison, the π-conjugated phenyl linker (HC-A3) previously developed by our group was also used as a coadsorbent. The structural effects on the photophysical and electrochemical properties and DSSC performance were systematically investigated. As a result, the DSSCs based on HC-A4 and HC-5 displayed power conversion efficiencies (PCEs) of 8.2% and 5.1%, respectively, while the HC-A3-based DSSC achieved a PCE of 7.7%. In the case of HC-A4, both the short-circuit photocurrent densities (J_sc) and open-circuit voltages (V_oc) of DSSCs were simultaneously improved to a large extent due to the more effective prevention of π−π stacking of organic dye molecules and the better light-harvesting effect at short wavelengths. The HC-A5-based DSSC exhibited a much lower short-circuit current (J_sc) and open-circuit voltages (V_oc) compared to the HC-A4-based DSSC, due to the fact that the dihedral angle of the π-conjugated linkers was too high for electron injection into the TiO₂ conduction band (CB) level. This had a reduced effect on preventing the π−π stacking of dye molecules, resulting in lower J_sc and V_oc values.     

D-A-D-A-D push pull organic small molecules based on 5,10-dihydroindolo[3,2-b]indole (DINI) central core donor for solution processed bulk heterojunction solar cells

Two D-A-D-A-D small molecules based on same 5,10-dihydroindolo [3,2-b]indole central donor core and different benzothiadiazole (BT) and fluorine substituted BT (FBT) acceptor units, denoted as p-DINI-(BTTh₃)₂ (1) and p-DINI-(FBTTTh₃)₂ (2), respectively were synthesized and their optical and electrochemical properties were investigated. These molecules were applied as donor along with PC₇₁BM as electron acceptor for the fabrication of solution processed bulk heterojunction organic solar cells. The solar cells prepared from the optimized active blended layer (1:2) cast from dichlorobenzene (DCB) showed overall power conversion efficiency (PCE) of 2.02% and 2.70% for 1 and 2, respectively as donor. The higher PCE of 2 as compared to 1 is attributed to the higher hole mobility and broader IPCE spectra. In order to improve the PCE we have employed a two step treatment of active layer i.e. solvent vapor annealing after thermal annealing (SVA-TA) and the PCE has been enhanced up to 4.14% and 5.27% for optimized 1:PC₇₁BM and 2:PC₇₁BM active layers, respectively. The improvement in the PCE has been resulted from the improvement in the balanced charge transport and better crystallinity of the donor in the blended active layer.     

Manipulating the LUMO distribution of quinoxaline-containing architectures to design electron transport materials: Efficient blue phosphorescent organic light-emitting diodes

A series of new quinoxaline-containing compounds, namely, 2,3,6,7-tetrakis(3-(pyridin-3-yl)phenyl)quinoxaline (Tm3PyQ), 2,3,6,7-tetrakis(3-(pyridin-4-yl)phenyl)quinoxaline (Tm4PyQ), 1,4-bis(2,3-dimethyl-7-(pyridin-3-yl)quinoxalin-6-yl)benzene (3PyDQB), and 1,4-bis(2,3-dimethyl-7-(pyridin-4-yl)quinoxalin-6-yl)benzene (4PyDQB) were designed and synthesized as electronic transporting materials. The lowest unoccupied molecular orbital (LUMO) distributions of these compounds vary with the locations of quinoxaline moieties, which result in adjustable intermolecular charge-transfer integrals. All the compounds exhibit favorable electron affinity (2.73–2.88 eV) and good thermostability (glass transition temperatures in the range of 112–148 °C). Using these compounds as electron transport layers, the bis(4,6-(difluorophenyl)pyridinato-N,C^2′)picolinate iridium(Ⅲ) (Firpic)-based blue phosphorescent organic light emitting diodes (PhOLEDs) achieve good performances with a maximum current efficiency (η_c,max) of 30.2 cd A⁻¹ and a maximum external quantum efficiency (η_ext,max) of 14.2%. Moreover, these efficiencies reveal small roll-offs at high luminance.