Fundamental insight into excimer formation has been gained by using 9,10-bis4-(9-carbazolyl)phenylanthracene (
) as a probe.
exhibits a highly emissive blue fluorescence in solution and is found to ...emit a panchromatic white light spectrum (400-750 nm) in film, powder and single crystal, in which an additional excimer band appears at ∼550 nm. Detailed structural analyses, emission relaxation dynamics and a theoretical approach conclude the formation of an anthracene*/phenyl ring excimer through an overlap between π* (anthracene) and π (phenyl ring) orbitals in a face-to-edge stacking orientation. The rate of excimer formation is determined to be 2.2 × 10
s
at room temperature, which requires coupling with lattice motion with an activation energy of 0.44 kcal mol
. Exploiting
as a single emitter, a fluorescent white organic light emitting diode (WOLED) is fabricated with a maximum external quantum efficiency (
) of 3.6% at 1000 cd m
(4.2 V) and Commission Internationale de L'Eclairage (CIE) coordinates of (0.30, 0.33). The white-light
reveals a preferred orientation of the transition dipole moment in the emitting layer to enhance light outcoupling. This non-doped, single component (
) WOLED greatly reduces the complexity of the fabrication process, rendering a green and cost-effective alternative among the contemporary display/lighting technologies.
A visible-light initiated oxidative cyclization of phenyl propiolates with sulfinic acids has been developed. The arylsulfonylation of alkynes was performed at room temperature under metal-free ...conditions to generate coumarin derivatives with wide functional group tolerance, good yields and high regioselectivity.
Excitation energy transfer in perylene-3,4:9,10-bis(dicarboximide) (PDI) aggregates is of interest for light-harvesting applications of this strongly absorbing and π-π stacking chromophore. Here we ...report the synthesis and characterization of two PDI dimers in which the chromophores are covalently linked by a redox-inactive triptycene bridge in orientations that are cofacial (1) and slip-stacked along their N-N axes (2). Femtosecond transient absorption experiments on 1 and 2 reveal rapid exciton delocalization resulting excimer formation. Cofacial π-π stacked dimer 1 forms a low-energy excimer state absorption (λmax = 1666 nm) in τ = ∼2 ps after photoexcitation. Inserting a phenyl spacer on the bridge to generate a slip-stacked PDI-PDI geometry in 2 results in a less stable excimer state (λmax = 1430 nm), which forms in τ = ∼12 ps due to decreased electronic coupling. The near-infrared (NIR) excimer absorption of cofacial dimer 1 is ∼120 meV lower in energy than that of slip-stacked dimer 2, further highlighting electronic differences between these states.
2,3-Diphenylcyclopropenone (1) reacts with N-imidoylthioureas 2a-e to form the pyrimidin-4(3H)-ones 5a-e. The reaction mechanism can be described as due to stepwise addition accompanied by ...elimination of phenyl isothiocyanate.
We recently reported a reaction sequence that activates C–H bonds in simple arenes as well as the N–N triple bond in N2, delivering the aryl group to N2 to form a new N–C bond (Nature 2020, 584, ...221). This enables the transformation of abundant feedstocks (arenes and N2) into N-containing organic compounds. The key N–C bond forming step occurs upon partial silylation of N2. However, the pathway through which reduction, silylation, and migration occurred was unknown. Here, we describe synthetic, structural, magnetic, spectroscopic, kinetic, and computational studies that elucidate the steps of this transformation. N2 must be silylated twice at the distal N atom before aryl migration can occur, and sequential silyl radical and silyl cation addition is a kinetically competent pathway to a formally iron(IV)–NN(SiMe3)2 intermediate that can be isolated at low temperature. Kinetic studies show its first-order conversion to the migrated product, and DFT calculations indicate a concerted transition state for migration. The electronic structure of the formally iron(IV) intermediate is examined using DFT and CASSCF calculations, which reveal contributions from iron(II) and iron(III) resonance forms with oxidized NNSi2 ligands. The depletion of electron density from the Fe-coordinated N atom makes it electrophilic enough to accept the incoming aryl group. This new pathway for the N–C bond formation offers a method for functionalizing N2 using organometallic chemistry.
The similarity of thermally activated delayed fluorescence (TADF) dyes and their hosts as pure organic molecules makes hosts predominant in intermolecular interactions and crucial to exciton ...harvesting and utilization in TADF diodes.
is the most popular high-energy-gap blue TADF host with steric
-substituted diphenylphosphine oxide (DPPO) groups for intermolecular interaction suppression, but suffers from serious efficiency roll-off due to its weak electroactivity. On the contrary,
-substituted DPPO with small steric hindrance is superior in intramolecular electronic coupling. In this work, four constitutional isomers of
are constructed as diphenylether (
) with two diphenylphosphine oxide (DPPO) groups substituted at either the 2 or 4 position, namely
(
),
,
and
, respectively. On the basis of separation configuration, the steric effect and electroactivity of
- and
-substituted DPPOs are successfully integrated in
, accompanied by remarkably reduced intermolecular interactions due to its unsymmetrical configuration. Compared to its congeners,
has a rigid structure and locally excited states similar to
for interaction suppression and improved charge mobility comparable to
for charge flux balance. Significantly, by virtue of the predominant orientation effect of
-DPPO on the T
location, its T
state is extremely condensed onto a single phenyl, protected from intermolecular interactions by its remaining five phenyls at its maximum extent. Consequently,
endowed its
-based deep-blue devices with state-of-the-art performance, including high color purity with chromaticity coordinates of (0.16, 0.17), external quantum efficiency (EQE) beyond 20% and EQE roll-off as low as 32% at 1000 cd m
. It is shown that the device performance of
was far beyond simple integration of those of
and
, verifying the significance of host optimization.
The article addresses the formation mechanisms of naphthalene and indene, which represent prototype polycyclic aromatic hydrocarbons (PAH) carrying two six-membered and one five- plus a six-membered ...ring. Theoretical studies of the relevant chemical reactions are overviewed in terms of their potential energy surfaces, rate constants, and product branching ratios; these data are compared with experimental measurements in crossed molecular beams and the pyrolytic chemical reactor emulating the extreme conditions in the interstellar medium (ISM) and the combustion-like environment, respectively. The outcome of the reactions potentially producing naphthalene and indene is shown to critically depend on temperature and pressure or collision energy and hence the reaction mechanisms and their contributions to the PAH growth can be rather different in the ISM, planetary atmospheres, and in combustion flames at different temperatures and pressures. Specifically, this paradigm is illustrated with new theoretical results for rate constants and product branching ratios for the reaction of phenyl radical with vinylacetylene. The analysis of the formation mechanisms of naphthalene and its derivatives shows that in combustion they can be produced via hydrogen-abstraction-acetylene-addition (HACA) routes, recombination of cyclopentadienyl radical with itself and with cyclopentadiene, the reaction of benzyl radical with propargyl, methylation of indenyl radical, and the reactions of phenyl radical with vinylacetylene and 1,3-butadiene. In extreme astrochemical conditions, naphthalene and dihydronaphthalene can be formed in the C6H5 + vinylacetylene and C6H5 + 1,3-butadiene reactions, respectively. Ethynyl-substituted naphthalenes can be produced via the ethynyl addition mechanism beginning with benzene (in dehydrogenated forms) or with styrene. The formation mechanisms of indene in combustion include the reactions of the phenyl radical with C3H4 isomers allene and propyne, reaction of the benzyl radical with acetylene, and unimolecular decomposition of the 1-phenylallyl radical originating from 3-phenylpropene, a product of the C6H5 + propene reaction, or from C6H5 + C3H5.
Improving the fill factor (FF) is known as a challenging issue in organic solar cells (OSCs). Herein, a strategy of extending the conjugated area of end‐group is proposed for the molecular design of ...acceptor–donor–acceptor (A–D–A)‐type small molecule acceptor (SMA), and an indaceno1,2‐b:5,6‐b′dithiophene‐based SMA, namely IDTN, by end‐capping with the naphthyl fused 2‐(3‐oxocyclopentylidene)malononitrile is synthesized. Benefiting from the π‐conjugation extension by fusing two phenyls, IDTN shows stronger molecular aggregation, more ordered packing structure, thus over one order of magnitude higher electron mobility relative to its counterpart. By utilizing the fluorinated polymer (PBDB‐TF) as the electron donor, the corresponding device exhibits a high efficiency of 12.2% with a record‐high FF of 0.78, which is approaching the theoretical limit of OSCs. Compared with the reference molecule, such a high FF in the IDTN system can be mainly attributed to the more ordered π–π packing of acceptor aggregates, higher domain purity and symmetric carrier transport in the blend. Hence, enlarging the conjugated area of the terminal‐group in these A–D–A‐type SMAs is a promising approach not only for enhancing the electron mobility, but also for improving the blend morphology, and both of them are conducive to the fill‐factor breakthrough.
By extending the conjugated area of the end‐group, a newly designed A–D–A–type small‐molecule acceptor, namely IDTN, exhibits dense and ordered packing, and therefore, the electron mobility of the IDTN is over one order of magnitude higher than that of its counterpart. When blended with the donor polymer PBDB‐TF, a high efficiency of 12.2% with an outstanding fill factor of 0.78 is achieved.
With 2-(2,4-difluorophenyl)pyridine (dfppy) as the first cyclometalated ligand and different monoanionic N-heterocyclic carbenes (NHCs) as the second cyclometalated ligands, 16 blue or greenish-blue ...neutral iridium(III) phosphorescent complexes, (dfppy)2Ir(NHC), were synthesized efficiently. The obtained Ir(III) complexes display typical phosphorescence of 455–485 nm with quantum yields up to 0.73. By modifying the phenyl moiety in the NHCs with electron-withdrawing substituents (e.g., −F or −CF3) or replacing it with N-heteroaromatic rings (pyridine or pyrimidine), the HOMO–LUMO gaps are broadened, and the emissions shift to the more blue region accordingly. Furthermore, to extend the application scope of NHCs as the second cyclometalated ligands, five other Ir(III) complexes from blue to red were synthesized with different first cyclometalated ligands. Finally, the organic light-emitting diodes using one blue emitter exhibit a maximum current efficiency of 37.83 cd A–1, an external quantum efficiency of 10.3%, and a maximum luminance of 8709 cd m–2. Our results demonstrate that NHCs as the second cyclometalated ligands are good candidates for the achievement of efficient phosphorescent Ir(III) complexes and corresponding devices.
Achieving a selective 2 e− or 4 e− oxygen reduction reaction (ORR) is critical but challenging. Herein, we report controlling ORR selectivity of Co porphyrins by tuning only steric effects. We ...designed Co porphyrin 1 with meso‐phenyls each bearing a bulky ortho‐amido group. Due to the resulted steric hinderance, 1 has four atropisomers with similar electronic structures but dissimilar steric effects. Isomers αβαβ and αααα catalyze ORR with n=2.10 and 3.75 (n is the electron number transferred per O2), respectively, but ααββ and αααβ show poor selectivity with n=2.89–3.10. Isomer αβαβ catalyzes 2 e− ORR by preventing a bimolecular O2 activation path, while αααα improves 4 e− ORR selectivity by improving O2 binding at its pocket, a feature confirmed by spectroscopy methods, including O K‐edge near‐edge X‐ray absorption fine structure. This work represents an unparalleled example to improve 2 e− and 4 e− ORR by tuning only steric effects without changing molecular and electronic structures.
Cobalt porphyrin atropisomers with similar electronic structures but dissimilar steric effects were synthesized. One isomer is selective for the 2 e− ORR, one is selective for the 4 e− ORR, while the other two show poor selectivity for either 2 e− or 4 e− ORR.
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