Visible-light photoredox catalysis has been established as a popular and powerful tool for organic transformations owing to its inherent characterization of environmental friendliness and ...sustainability in the past decades. The thiol-ene/yne reactions, the direct hydrothiolation of alkenes/alkynes with thiols, represents one of the most efficient and atom-economic approaches for the carbon-sulfur bonds construction. In traditional methodologies, harsh conditions such as stoichiometric reagents or a specialized UV photo-apparatus were necessary suffering from various disadvantages. In particular, visible-light photoredox catalysis has also been demonstrated to be a greener and milder protocol for the thiol-ene/yne reactions in recent years. Additionally, unprecedented advancements have been achieved in this area during the past decade. In this review, we will summarize the recent advances in visible-light photoredox catalyzed thiol-ene/yne reactions from 2015 to 2021. Synthetic strategies, substrate scope, and proposed reaction pathways are mainly discussed.
The intense interest in organic light-emitting devices (OLEDs) originates from their attractive prospects as the next generation display and lighting technologies. The development of blue emitters is ...of great significance in OLED applications as full-color displays and energy-saving lightings. The electrofluorescence using triplet energy for radiation has recently become a spotlight in the area of organic electronics. Various triplet-to-singlet conversion mechanisms have been established, including triplet-triplet annihilation (TTA), thermally activated delayed fluorescence (TADF) and "hot exciton" model with hybridized local and charge-transfer (HLCT) excited state, and they are expected to shed light on the development on blue OLEDs. This study revolves around the recent progress in blue electrofluorescence materials utilizing triplet excitons for radiation. Owing to the page limitation, special focus is placed on small molecule-based purely organic fluorophores with breakthrough device performances. We begin with the general information of blue-emitting organic electrofluorescence devices, and then give an overview of blue fluorescence OLEDs based on different electroluminescence mechanisms, which is followed by individual molecular design strategies towards high efficiency.
The recent progress in blue-emitting organic electrofluorescence materials with high performance using triplet excitons is reviewed.
High‐performance deep‐blue emitters with external quantum efficiencies (EQEs) exceeding 5 % are still scarce in organic light‐emitting diodes (OLEDs). In this work, by introducing a ...1,2,4triazolo1,5‐a pyridine (TP) unit at the N1 position of phenanthroimidazole (PI), two luminescent materials, PTPTPA and PTPTPA, were obtained. Systematic photophysical analysis showed that the TP block is suitable for constructing hybridized local and charge‐transfer (HLCT) emitters. Its moderate electron‐withdrawing ability and rigid planar structure can enhance the CT component while ensuring color purity. In addition, compared with PTPTPA, the additional phenyl ring of PTPBPTA not only increased the oscillator strength, but also decreased the Stokes shift. TDDFT calculations pointed out facile reverse intersystem crossing processes in PTPTPA from high‐lying triplet states to the singlet excited state. A nondoped device based on PTPTPA as emitter showed impressive performance with EQEmax of 7.11 % and CIE coordinates of (0.15, 0.09). At the same time, it was also an efficient host for yellow and red phosphorescent OLEDs. By doping yellow (PPYBA) and red (BTPG) phosphorescent dyes into PTPTPA, a white OLED with a high EQE of 23.85 % was achieved. The successful design of PTPTPA not only provided an optimization choice for OLED emitters, but also demonstrated the empirical rules for the design of multifunctional deep‐blue emitters.
Deeper blue: On the basis of multifunctional phenanthroimidazole‐based material PTPBPTA, which acts both as a deep‐blue fluorescent emitter and as a host material for phosphors, high‐performance deep‐blue fluorescent organic light‐emitting diodes (OLEDs), yellow and red phosphorescent OLEDs, and a white OLED were fabricated.
By utilizing the bipolarity of 1,2‐diphenylphenanthroimidazole (PPI), two types of asymmetrical tripartite triads (PPI‐TPA and PPI‐PCz) were designed with triphenylamine (TPA) and 9‐phenylcarbazole ...(PCz). These triads are deep‐blue luminescent materials with a high fluorescence quantum yield of nearly 100 %. To trace the photophysical behaviors of these triads, their excited‐state evolution channels and interchromophoric interactions were investigated by ultrafast time‐resolved transient absorption and excited‐state theoretical calculations. The results suggest that the electronic nature, asymmetrical tripartite structure, and electron–hole distance of these triads, as well as solvent polarity, determine the lifetime of intramolecular charge transfer (ICT). Interestingly, PPI‐PCz triads show anti‐Kasha ICT, and the charge‐transfer direction among the triads is adjustable. For the PPI‐TPA triad, the electron is transferred from TPA to PPI, whereas for the PPI‐PCz triad the electron is pushed from PPI to PCz. Exploration of the excited‐state ICT in these triads may pave the way to design better luminescent materials in the future.
Deeper blue: Two types of asymmetrical tripartite triads (PPI‐TPA and PPI‐PCz) were designed as deep‐blue luminescent materials with a high fluorescence quantum yield of nearly 100 %. The electronic nature of the moieties, asymmetrical tripartite structure, and electron‐hole distance of these triads, as well as the polarity of the solvent, determine the lifetimes of excited‐state intramolecular charge transfer (ICT). Interestingly, the CT direction among the triads is adjustable.
To achieve high‐efficiency deep‐blue electroluminescence satisfying Rec.2020 standard blue gamut, two thermally activated delayed fluorescent (TADF) emitters are developed: ...5‐(2,12‐di‐tert‐butyl‐5,9‐dioxa‐13b‐boranaphtho3,2,1‐deanthracen‐7‐yl)‐10,10‐diphenyl‐5,10‐dihydrodibenzob,e1,4azasiline (TDBA‐PAS) and 10‐(2,12‐di‐tert‐butyl‐5,9‐dioxa‐13b‐boranaphtho3,2,1‐deanthracen‐7‐yl)‐9,9‐diphenyl‐9,10‐dihydroacridine (TDBA‐DPAC). Inheriting from their parented organoboron multi‐resonance core, both emitters show very promising deep‐blue emissions with relatively narrow full width at half‐maximum (FWHM, ≈50 nm in solution), high photoluminescence quantum yield (up to 92.3%), and short emission lifetime (≤2.49 µs) with fast reverse intersystem crossing (>106 s−1) in doped films. More importantly, replacing the spiro‐centered sp3 C atom (TDBA‐DPAC) with the larger‐radius sp3 Si atom (TDBA‐PAS), enhanced conformational heterogeneities in bulky‐group‐shielded TADF molecules are observed in solution, doped film, and device. Consequently, OLEDs based on TDBA‐PAS retain high maximum external quantum efficiencies ≈20% with suppressed efficiency roll‐off and color index close to Rec.2020 blue gamut over a wide doping range of 10–50 wt%. This study highlights a new strategy to restrain spectral broadening and redshifting and efficiency roll‐off in the design of deep‐blue TADF emitters.
Conformational heterogeneity in bulky‐group‐shielded deep‐blue thermally activated delayed fluorescent emitters enables suppression of spectral broadening, redshifting, and concentration quenching. Devices based on the emitter present high external quantum efficiency up to 22.35% with suppressed efficiency roll‐off and color indices close to Rec.2020 blue gamut over a wide doping range of 10–50 wt%.
Herein, we reported a dual-catalytic platform for the allylation of amines and sulfonyl hydrazines with olefins to selectively access α-allylic amines and allylic sulfones in good yields by combining ...photoredox catalysis and cobaloxime catalysis. This strategy avoided the use of a stoichiometric amount of terminal oxidant and the use of pre-functionalized allylic precursors, representing a green and ideal atom- & step-economical process. Good substrate scope and gram-scale synthesis demonstrated the utility of this protocol. Mechanistic studies revealed that a radical process is probably involved in this reaction.
Herein, a photoredox/cobaloxime co-catalyzed allylation of amines and sulfonyl hydrazines with olefins to access
α
-allylic amines and allylic sulfones is described, which avoided the external oxidants and pre-functionalized allylic precursors.
Efficient multifunctional materials acting as violet‐blue emitters, as well as host materials for phosphorescent OLEDs, are crucial but rare due to demand that they should have high first singlet ...state (S1) energy and first triplet state (T1) energy simultaneously. In this study, two new violet‐blue bipolar fluorophores, TPA‐PI‐SBF and SBF‐PI‐SBF, were designed and synthesized by introducing the hole transporting moiety triphenylamine (TPA) and spirobifluorene (SBF) unit that has high T1 into high deep blue emission quantum yield group phenanthroimidazole (PI). As the results, the non‐doped OLEDs based on TPA‐PI‐SBF exhibited excellent EL performance with a maximum external quantum efficiency (EQEmax) of 6.76 % and a violet‐blue emission with Commission Internationale de L′Eclairage (CIE) of (0.152, 0.059). The device based on SBF‐PI‐SBF displayed EQEmax of 6.19 % with CIE of (0.159, 0.049), which nearly matches the CIE coordinates of the violet‐blue emitters standard of (0.131, 0.046). These EL performances are comparable to the best reported non‐doped deep or violet‐blue emissive OLEDs with CIEy<0.06 in recent years. Additionally, the green, yellow and red phosphorescent OLEDs with TPA‐PI‐SBF and SBF‐PI‐SBF as host materials achieved a high EQEmax of about 20 % and low efficiency roll‐off at the ultra‐high luminance of 10 000 cd m−2. These results provided a new construction strategy for designing high‐performance violet‐blue emitters, as well as efficient host materials for phosphorescent OLEDs.
The non‐doped device based on TPA‐PI‐SBF as emitter exhibited a maximum external quantum efficiency (EQEmax) of 6.76 % with Commission Internationale de L′Eclairage (CIE) of (0.152, 0.059). As host material, the green, yellow, and red phosphorescent OLEDs obtained high EQEmax of about 20 % and both devices exhibited low efficiency roll‐off.
A photoredox/cobaloxime co-catalyzed coupling reaction of α-ketoacids and methacrylates to obtain allylic ketones is described. Without the cobaloxime catalyst, 1,4-dicarbonyl compounds are ...generated. The cobaloxime catalyst enables dehydrogenation to generate the formation of new olefins. The generality, good substrate scope and mild conditions are good features in the photoredox/cobaloxime catalysis protocol, and this method will provide new opportunities for the functionalization of more olefins.
The selective synthesis of allylic ketones and 1,4-dicarbonyl compounds by photoredox/cobaloxime co-catalysis and photoredox catalysis, respectively, is described herein.
The first example of using commercially available and cheap
n
Bu
4
NBr as a cocatalyst, which is photoactivated by 4-CzIPN, to selectively activate the α-C-H bond of tetrahydrofuran for C-S and C-C ...cross-couplings is reported herein. This transition-metal free strategy features operational simplicity, mild and inherent green conditions as well as broad substrate scope.
A simple and inherent green photocatalytic approach using commercially available and cheap
n
Bu
4
NBr with 4-CzIPN was reported to effectively initiate the site-selective
α
-C(sp
3
)-H activation of tetrahydrofuran for C-S and C-C cross-couplings.
The built‐in electric field of the polymer semiconductors could be regulated by the dipole moment of its building blocks, thereby promoting the separation of photogenerated carriers and achieving ...efficient solar‐driven water splitting. Herein, three perylene diimide (PDI) polymers, namely oPDI, mPDI and pPDI, are synthesized with different phenylenediamine linkers. Notably, the energy level structure, light‐harvesting efficiency, and photogenerated carrier separation and migration of polymers are regulated by the orientation of PDI unit. Among them, oPDI enables a large dipole moment and robust built‐in electric field, resulting in enhanced solar‐driven water splitting performance. Under simulated sunlight irradiation, oPDI exhibits the highest photocurrent of 115.1 μA cm−2 for photoelectrochemical oxygen evolution, which is 11.5 times that of mPDI, 26.8 times that of pPDI and 104.6 times that of its counterparts PDI monomer at the same conditions. This work provides a strategy for designing polymers by regulating the orientation of structural units to construct efficient solar energy conversion systems.
Three perylene diimide (PDI) polymers were designed and synthesized such that the molecular orientation of the PDI units was regulated to create and modulate their built‐in electric fields. Due to the large dipole moment and interfacial electric field, oPDI enables an extraordinary photocurrent density of 115.1 μA ⋅ cm−2, which is 11.5 and 26.8 times that of mPDI and pPDI, respectively.
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