Research discoveries in carbon nanostructures have encouraged scientists to look for the next generation of inexpensive, versatile nanomaterials. One element that has become of great interest in the last few years is phosphorus. Although studies investigating phosphorus nanostructures and properties are still in their infancy, unique properties of various phosphorus nanostructures are expected. In this review, we intend to summarize some optical and optoelectronic applications of both black and red phosphorus. The role of phosphorus as a photocatalyst is also discussed.
In this review, the main progresses on the chemical and photochemical synthesis of thiophene-based helicenes are described. In the section of chemical method for synthesis of helicenes, based on ditheinothiophene (DTT) as building blocks, the single helicenes are normally designed and synthesized to make bi-DTT as precursor first, and then implement sulfur substituted cyclization for target helicenes. However, it may not be successful for making longer and longer helicenes due to the increasing intramolecular interactions between the two moieties of precursor molecule. By the synthetic strategy of increasing the solubilizing groups in making helicenes, the target molecular structures can be changed from single helicenes to double helicenes. In the section of photochemical synthesis of helicenes, the oxidative photocyclization is confirmed to be an effective method for preparation of helicenes. Due to the double radical mechanism in the photochemistry of double bond under irradiation, the cyclization step gives the effective target products including both racemate and mesomer at the same time. In addition, the prospects for the field of thiophene-based helicenes are put forward in three aspects:1) design the new isomers of helicenes based on the position isomerism of sulfur atoms in the terminal thiophene rings of helicene; 2) design and synthesis of double or multiple helicenes with new structures; 3) find the application of helicene enantiomers in asymmetric catalysis, chiral assembly and so on.
Visible-light photoredox catalysis, which shows typical features of clean and energy-saving procedures, excellent functional group tolerance, and high chemical selectivities, is a novel and powerful organic synthesis method. As a cheap, ecologically benign oxidant, the combination of aerobic oxidation with visible-light photoredox catalysis greatly promotes the development of green chemistry. This review briefly summarizes recent achievements in the area of visible-light-driven aerobic oxidation by our laboratory and also give its outlook in the future.
Complementary to the transition metal-catalyzed cross-coupling reactions, merging visible light photoredox and nickel catalysis is an enabling strategy for constructing carbon-carbon bonds. With promising potential for future development and applications, this area has been rapidly advancing at the forefront of organic photosynthesis research in recent years. Here we summarize the current state-of-the-art based on mode of reaction designs.
The synthesis of inorganic nanomaterials is one of the prerequisites and bases for the development of nanoscience. Different from the wet-chemical method at elevated temperature, the photochemical method reveals some unique characteristics in the synthesis of inorganic nanomaterials, and has attracted extensive attention in recent years. This paper reviews the applications of photochemical method in the synthesis of inorganic nanomaterials in recent years in three parts, including photochemical synthesis and loading of noble metal nanomaterials, photochemical synthesis of semiconductor nanomaterials, and plasmon-mediated photochemical synthesis of anisotropic metal nanocrystals. At last, on the basis of summarizing the advantages of photochemical method in the synthesis of inorganic nanomaterials and the shortcomings in the present studies, we prospect the possible direction of its development in the future.
Photocatalytic CO2 reduction is a major part of the study of artificial photosynthesis. The conversion of molecule CO2 into fuels, precursor to fuels, or value-added chemicals through visible light induced photocatalysis is considered as an ideal way of fixation and resource utilization of CO2. Metal complexes as molecular catalysts for CO2 reduction had long been used in photocatalytic CO2 reduction systems for its tunable structure, rich valences of contained metal, easy synthesis, and economic advantages. The study of utilization of cobalt complexes as catalysts for photocatalytic CO2 reduction dates from 1980s. A large number of cobalt complexes of Co-macrocycles, Co-porphyrin and its analogues, Co-polypyridine complexes had been developed as catalysts to mediate CO2-CO or CO2-formate conversion in particular photocatalytic CO2 reduction systems. Herein, we review the development and advances of the study on molecular systems for photocatalytic CO2 reduction based on cobalt complexes as catalysts. The cobalt complexes used in photocatalytic CO2 reduction systems are classified and discussed. The structures, mechanisms, and composition of systems are reviewed. In the end of the review, a summary and outlook are given.
C=C double bond isomerization (DBI) is a method for synthesizing new organic compounds from olefins and theirs derivatives, which was based on C=C migration along carbon chain and cis/trans transform, and it plays an important role in the fields of organic synthesis, synthesis of daily chemicals, raw oil's development and synthesis of natural products and so on. In this paper, advances of five types of catalytic methods for DBI of olefins and its derivatives since 1960s were discussed in detail; Based on his recent work, the author mainly introduces application and development of photo catalysis in DBI of olefins and theirs derivatives.
The key process in the synthesis of vitamin D3 is the photochemical conversion from 7-dehydrocholesterol to pre-vitamin D3, which is currently carried out in batch photoreactors and suffers from low conversion efficiency, recycle of unreacted 7-dehydrocholesterol, and long production period. Using micro-flow photoreactor instead of batch photoreactor, the conversion yield of 7-dehydrocholesterol may be increased from less than 30% to over 95%,allowing the photoreaction product to be directly used to prepare resin-like vitamin D3 through a thermal isomerization reaction and shortening the production period greatly.
PMI-(iPr)2An (PSⅡ) and PMI-((iPr)2An)2(PSⅢ)) with strong visible light absorption and good solubility are successfully synthesized through the chemically modifications of Perylene-3,4,9,10-tetracarboxylicdianhydride. Under visible light irradiation, sulfides are transformed to sulfoxides with relatively high selectivity and yield, in which PSⅡ or PSⅢ act as the photosensitizer and oxygen plays the role of oxidant. Under optimized conditions, both the yield and selectivity can reach up to 100% for sulfides oxidation by using PSⅢ as the photosensitizer. Active species trapping experiments and electron spin resonance (ESR) demonstrate that the singlet oxygen and superoxide radical anion are the effective oxidants during the photocatalyticreaction.
Based on the same benzothiadiazole (BTD) ligand (H2L=2,1,3-benzothiadiazole-4,7-dicarboxylic acid), two new 3D BTD-derived Cd(Ⅱ) metal-organic frameworks 1[Cd4(BTDC)4·5H2O] and 2[Cd2(BTDC)2(DMF)·1.5H2O] were obtained by the different solvothermal reactions. Interestingly, in 1, partial BTD units arranged in an anti-parallel mode, and the distance between these BTD units was 3.987 Å, which was less than that valued by theoretical calculation (4 Å). Furthermore, evidencedby UV-Vis solid state absorption spectra of 1, the energy of absorption band at 470 nm was lower than those from typical monomer-BTD unit. Hence, the structural analysis and photophysical study distinctly demonstrated the evidence of BTD anti-dimmerin 1. More importantly, the UV and fluorescence spectra after illumination showed that there were interesting photochromic phenomena in both complexes 1 and 2 triggered by photoinduced electron transfer, where anionic radical was also directly observed by the electron paramagnetic resonance (EPR) spectra before and after the illumination. Herein, FT-IR spectra show that the subsequent decarboxylation of ligand unit results to release CO2 gas (2331 cm-1, 2361 cm-1) in complexes 1 and 2.
Novel electron acceptor 2,2-dimethyl-1,3-dione is synthesized and applied for thermally activated delayed fluorescence (TADF) molecular design. We synthesized a series of TADF molecules based on 2,2-dimethyl-1,3-dione with different emission color:IDYD, IDPXZ and ID2PXZ. The organic light emitting diodes (OLEDs) device based on IDYD exhibits blue emission with CIE coordinate of (0.27, 0.31), and the maximum external quantum efficiency (EQE) reaches 2.13%. While the OLEDs device based on IDPXZ exhibits orange emission with CIE coordinate of (0.43,0.53) and the maximum external quantum efficiency (EQE) reaches 1.31%. For the OLEDs device based on ID2PXZ exhibits yellow emission with CIE coordinate of (0.41, 0.54), and the maximum external quantum efficiency (EQE) reaches 2.55%. The results show that 2,2-dimethyl-1,3-indenone can be used as an electron acceptor for TADF molecule design and have a decent prospect in full-color OLEDs devices.
ZnO and ZnS are both important Ⅱ-Ⅵ wide bandgap semiconductors. Their heterostructures have Type-Ⅱ band alignment, which contributes to better charge separation efficiencies and longer charge lifetimes. In this work, a simple physical vapor deposition method was used to grow ZnS single-crystalline membrane on ZnO bulk substrates. The ZnS film was composed of ultrathin 4 nm-thick equilateral ZnS triangles. This is the first report of synthesis of two-dimensional ultra-thin ZnS materials. XRD and TEM results reveal the epitaxial growth behavior of ZnS on ZnO substrates. After ZnS coating, the intensities of visible photoluminescence peak increased dramatically, which can be attributed to the defects introduced during the growth. An ultraviolet photodetector was assembled using the heterostructure, and its photodetection properties were evaluated. The results showed that the heterostructure can detect ultraviolet light of broad range of wavelengths, and the rising time and the decay time were 200 ms and 1050 ms, respectively, indicating that ZnO/ZnS large-area single-crystalline heterostructuresare promising candidates for optoelectronic applications.
Efficient deep-blue organic emitters are of particular significance in organic electroluminescence. In this work, by using an asymmetrically twisted and rigid molecular design strategy, a high-efficiency deep-blue bisphenanthroimidazole emitter, MBTPI, was successfully synthesized, characterized and applied in a high-performance deep-blue organic light-emitting device (OLED). It shows high decomposition temperature (496℃) and high glass transition temperature (190℃), which are favorable for device stability. Its molecular conjugation was efficiently controlled by an asymmetrically twisted and rigid molecular structure, which makes its emission band locates at deep blue region, and solid film emission quantum yield is as high as 74%. Theoretical calculation also proves the presence of asymmetrically twisted rigid molecular structure, and the methyl dose change the molecular geometry, but has little influence on frontier orbital distribution, which is beneficial for maintaining good bipolar transporting property. MBTPI-based non-doped OLED displays a stable and highly efficient deep-blue electroluminescence with CIE coordinates (0.15, 0.07), which is very close to the NTSC deep-blue standard (0.14, 0.08). External quantum efficiency is high up to 4.91%, which is comparable to the state-of-the-art deep-blue non-doped OLEDs with CIEy lower than 0.08.
Phosphorescent organic light-emitting diodes (OLEDs) are advantageous over the traditional fluorescent ones in terms of high efficiency by harvesting both singlet and triplet excitons for light emission. Transition-metal complex phosphors must be dispersed in a certain host matrix to suppress the concentration quenching and triplet-triplet annihilation. Therefore, the host material is as important as the dopant emitter in phosphorescent OLEDs. In this report, a novel host material, oCzTz, was developed by using 1,2,4-triazole as the n-type unit and carbazole as the p-type unit. Ortho-substitution was applied to reach a twisted molecular configuration, which finally leads to high triplet energy of 3.01 eV for oCzTz. oCzTz has high thermal decomposition temperature of 353℃ and glass transition temperature of 110℃. The theoretical calculation results showed that the HOMO and LUMO are highly separated, indicating its bipolar charge transporting feature. oCzTz was used as host material to fabricate sky-blue phosphorescent OLED with FIrpic as the doped emitter, which exhibited a low turn-on voltage of 3.4 V, the high current efficiency of 37.2 cd·A-1 and the power efficiency of 29.2 lm·W-1. These are one of the highest efficiencies among the sky-blue phosphorescent OLEDs with TPBI as electron transporting layer.
With the rapid development of high performance non-fullerene electron acceptor, the power conversion efficiency of polymer solar cells increased dramatically in the last few years, among which structurally non-planar electron acceptors play a very important role. In this paper, a new family non-fullerene electron acceptor based on 1,8-naphthalimide unit with cyclopenta[2,1-b;3,4-b']dithiophene(CPDT-(NMI)2), 4,4'-spiro-bi[cyclopenta[2,1-b;3,4-b']dithiophene](SCPDT-(NMI)4) or 4-H-cyclopenta-[2,1-b;3,4-b']dithiophene-4-one (CPDT-O-(NMI)2) core were synthesized. The absorption and fluorescence spectra, as well as the electrochemical properties of these compounds were characterized. Results showed that SCPDT-(NMI)4 showed a blue-shifted absorption compared to that of CPDT-(NMI)2, which is ascribed to the twisted molecular structure of CPDT-(NMI)2 for its high steric hindrance. While CPDT-O-(NMI)2 showed two absorption bands with peaking wavelength at 420 nm and 550 nm, which is quite different to that of SCPDT-(NMI)4 and CPDT-(NMI)2. Solid state absorption spectra confirm that SCPDT-(NMI)4 and CPDT-(NMI)2 showed low intermolecular interaction, which could be attributed to the non-planar molecular structure of these two compounds as well. Fluorescence of the SCPDT-(NMI)4 film was found to be red-shifted 11 nm over CPDT-(NMI)2, which is ascribed to the spiro-conjugation effect of SCPDT-(NMI)4 in excited state. Cyclic voltammetry results demonstrated that LUMO energy levels of these compounds are around -3.5 to -3.8 eV, making them suitable electron acceptor in polymer solar cells. Polymer solar cell using PBDB-T as the electron donor and SCPDT-(NMI)4 as the electron acceptor showed a high power conversion efficiency of 1.16%, which is much higher than that of CPDT-(NMI)2 (0.11%). Fluorescence of the blended films confirmed that photon induced electron transfer between PBDB-T and NMIs is not completed, which is believed to be one of the main reason for the low device performance.
A novel and simple method to control the crystallization process during the formation of perovskite thin films is critical for optimizing the device fabrication process and constructing high efficiency perovskite solar cells. In this article, a method of adjusting the vacuum was used to effectively control the crystallization process. Furthermore, the role of pressure and its influence upon perovskite crystal growth, film formation and device performance were systematically investigated. The crystallinity and morphology of the perovskite thin film were characterized by scanning electron microscope (SEM), ultraviolet-visible absorption spectra (UV-Vis) and X-ray diffraction (XRD). Based on the structure of Glass/ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al, the performance of the device corresponding to the different pressure was studied. The results indicate that the decreased pressure can enhance the crystallinity of the perovskite film obviously, and improve the surface coverage by reducing the amount of holes. At the same time, the short circuit current, filling factor and photoelectric conversion efficiency of the device are all improved with the pressure decreasing. A 19% higher power conversion efficiency of 12.36% was achieved in comparison to the device fabricated by traditional method, which exhibited just 10.38% efficiency.
Coaxial CoSe/TiN nanotube arrays have been designed for high performance counter electrodes of dye-sensitized solar cells. This hybrid counter electrodewas prepared by electrodepositing CoSe into TiN nanotube arrays, which are prepared by anodization of a Ti mesh substrate and subsequent nitridation using ammonia annealing. The CoSe/TiN counter electrode displayed excellent performance comparable to Pt/FTO counter electrode due to the effectively combined network of both high electrical conductivity and more favorable and efficient interfacial active sites. The energy conversion efficiency of the cell with CoSe/TiN/Ti as counter electrode reached 9.25%, which was superior to 8.09% of the cell with Pt/FTO counter electrode under the same experimental conditions. These results demonstrate that the coaxial composite nanostructureis very promising for the structure-controllable counter electrode (CE) material.
Based on easy and accessible Mannich reaction, we synthesized a[N2O2]-type ligand which was successfully coordinated with Ni(ClO4)2 to afford a nickle complex NiL. The ligand and the NiL complex was characterized by 1HNMR and HRMS. Electrochemical study indicates that the NiL complex exhibits excellent hydrogen production activity in neutral phosphate buffer.