Xuemei Pu

Fine tuning of emission color of iridium(III) complexes from yellow to red via substituent effect on 2-phenylbenzothiazole ligands: synthesis, photophysical, electrochemical and DFT study.

Four novel iridium(III) complexes bearing biphenyl (7a-7c) or fluorenyl (7d) modified benzothiazole cyclometallate ligands are synthesized. In comparison with the yellow parent complex, bis(2-phenylbenzothiozolato-N,C(2)) iridium(III) (acetylacetonate) [(pbt)(2)Ir(acac)] (λ(PLmax) = 557 nm, φ(PL) = 0.26), 7a-7d show 20-43 nm bathochromic shifted orange or red phosphorescence in solution, with maximum photoluminescence (PL) quantum yield of 0.62, and PL lifetime of 1.8-2.0 μs. Meanwhile, the resulting complexes also exhibit intense orange or red phosphorescence of λ(PLmax) = 588-611 nm in solid films. The complex 7c with two tert-butyl substituents possesses the highest phosphorescent efficiency both in dilute solution and thin solid films, therefore may be a prospective candidate for both doping and host emitting electrophosphorescent material. Furthermore, despite the observation of severe oxygen quenching for 7a-7d in solution, 7a and 7c even show efficient emission intensity quenching by oxygen in their solid state due to the existence of void channels in crystals; consequently, they are promising molecular oxygen sensor reagents. Electrochemical measurement and DFT calculation results suggest that all these chelates own declined LUMOs of 0.1 eV relative to that of (pbt)(2)Ir(acac) owing to the contribution of the phenyl substituents; whereas only 7d shows a more destabilized HOMO (∼0.1 eV) compared with the parent chelate.

Self-promoted phthalimide-containing phthalonitrile resins with sluggish curing process and excellent thermal stability

A novel unsymmetrical phthalimide-containing phthalonitrile (PIPN) was successfully synthesized. The chemical structure of the PIPN monomer was confirmed by various spectroscopic techniques. Rheology and differential scanning calorimetry (DSC) revealed that the self-promoted curing reaction of the PIPN was an extremely sluggish process. The fully cured PIPN polymers showed excellent thermal properties revealed by thermogravimetric analysis (TGA) and DSC. IR and solid-state UV-Vis diffusion reflectance spectra confirmed the formation of the triazine and phthalocyanine ring during the curing reaction. Rheometric studies suggested that the curing reaction of phthalonitrile with a phthalimide group was faster compared to the reaction with a benzimidazole ring, and a nucleophilic addition reaction mechanism was successfully introduced to explain this phenomenon.

Synthesis and photovoltaic properties of conjugated copolymers bearing planar acenaphtho[1,2-b]quinoxaline moiety with deep HOMO level

A series of alternating copolymers (PC-AQx, PT-DTAQx, PC-DTAQx, PF-DTAQx, and PBDT-DTAQx) bearing novel planar acenaphtho[1,2-b]quinoxaline (AQx) or 8,11-di(thiophen- 2-yl)acenaphtho[1,2-b]quinoxaline (DTAQx)-acceptor cores have been synthesized via Suzuki or Stille coupling reactions. UV–vis absorption and GIXRD characterization results indicated that the presence of planar DTAQx unit is favorable for the promotion of well-ordered interchain packing in the solid state, and the incorporation of planar electron-donating benzo[1,2-b: 4,5-b′]-dithiophene (BDT) moiety would be propitious to the molecular self-organization. Electrochemical measurement results suggested that four copolymers possess deep HOMO energy level of −5.5xa0~xa0−5.6xa0eV. The polymer solar cell with structure of ITO/PEDOT:PSS(30xa0nm)/polymer:PCBM (60xa0nm)/Bphen(10xa0nm)/Ag(100xa0nm) exhibited the highest Voc of 0.84xa0V with PF-DTAQx as p-type polymer, while the best power conversion efficiency (PCE) of 0.9xa0% was obtained using a blend of PBDT-DTAQx and PCBM (1:4) as active layer.

Iridium(III) complexes with enhanced film amorphism as guests for efficient orange solution-processed single-layer PhOLEDs with low efficiency roll-off

By introducing a phenyl substituent into the meta-site of the phenyl segment of the 2-phenylbenzothiazole ligand, two novel orange iridium(III) complexes, namely, (3Phbt)2Ir(acac) and (3OMePhbt)2Ir(acac), have been synthesized. Compared with their parent compound (bt)2Ir(acac), both of them possess much enhanced thermostability and film amorphism, making them suitable candidates as guests for high performance solution-processed phosphorescent organic light-emitting diodes (PhOLEDs). However, (4Phbt)2Ir(acac) bearing para-phenyl possesses worse processability relative to (bt)2Ir(acac) due to spontaneous crystallization stemming from the intense intermolecular interactions. Single-layer solution-processed PhOLEDs with (3Phbt)2Ir(acac) and (3OMePhbt)2Ir(acac) as guests show peak current efficiency of 17.2 cd A(-1) and 15.2 cd A(-1), and maximum brightness of 28,270 cd m(-2) and 27,900 cd m(-2), respectively. Both are greatly improved compared to the devices employing (bt)2Ir(acac) (10.2 cd A(-1) and 14,350 cd m(-2)) and (4Phbt)2Ir(acac) (5.0 cd A(-1) and 13,790 cd m(-2)) as phosphors. Moreover, quite low efficiency roll-off is acquired in these devices at high luminance. The much improved electroluminescence performances of these objective complexes could be mainly attributed to the presence of a rigid phenyl on the appropriate substitution site of the cyclometallate ligand, which leads to improved thermostability with compatible alleviated intermolecular interactions, and consequently enhanced film amorphism.

Simultaneous harvesting of triplet excitons in OLEDs by both guest and host materials with an intramolecular charge-transfer feature via triplet–triplet annihilation

A red naphthalimide derivative with an intramolecular charge-transfer (ICT) feature, namely (E)-2-(4-(t-butyl)phenyl)-6-(2-(6-(diphenylamino)naphthalen-2-yl)vinyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NA-TNA), was designed and synthesized. Photophysical and magneto-electroluminescence (MEL) characterization results revealed that NA-TNA could harvest triplet excitons via a triplet–triplet annihilation (TTA) process in organic light-emitting diodes (OLEDs) due to the presence of a lower-lying triplet excited state with 3ππ* character. Consequently, using NA-TNA as a guest compound and CzPhONI, another ICT-featured naphthalimide derivative with triplet fusion delayed fluorescence (TFDF) character as host material, a high-performance orange OLED with 6 wt% NA-TNA doped CzPhONI film as the emitting layer was acquired. The maximum current efficiency (LEmax), brightness (Lmax), and external quantum yield (EQEmax) of this OLED is 7.73 cd A−1, 31u2006940 cd m−2 and 5.83%, respectively, while the theoretical EQEmax of this device should not exceed 3.34%. On the contrary, the reference device with a NA-TNA doping level of 1.4 wt% showed much inferior performance, with a LEmax, a Lmax, and an EQEmax of 3.19 cd A−1, 24u2006900 cd m−2 and 2.49%, respectively. The high performance of the 6 wt% NA-TNA doped device was attributed to the efficient harvesting of triplet excitons by both the guest and host materials.

Self-assembled nanopillar arrays by simple spin coating from blending systems comprising PC61BM and conjugated polymers with special structure

Three conjugated D–A copolymers were found to form well-defined nanopillar arrays through facile spin-casting process when blended with fullerene derivatives. Research results indicate that the presence of large coplanar segments and intramolecular S⋯O attractive interactions in the polymers are both crucial factors for achieving self-assembled nanopatterned pillar arrays.