Highly efficient thermally activated fluorescence of a new rigid Cu(I) complex [Cu(dmp)(phanephos)]+

The rigid [Cu(dmp)(phanephos)]+ complex displays a high luminescence quantum yield of 80% at ambient temperature. In contrast to the long-lived phosphorescence of 240 μs at T < 120 K with a radiative rate of kr = 3 × 103 s−1, the ambient-temperature emission represents a thermally activated delayed fluorescence (DF) with a decay time of only 14 μs and a radiative rate of kr(DF) = 6 × 104 s−1. Evidence for the involvement of the excited singlet state in the emission process is presented. This material has high potential to be applied in efficient OLEDs taking advantage of the singlet harvesting mechanism

Cytotoxic Activities of Bis-cyclometalated Iridium(III) Complexes Containing Chloro-substituted kappa N-2-terpyridines

The synthesis and characterization of two new bis-cyclometalated compounds [Ir(ptpy)(2)(kappa N-2-terpy-C6H4Cl-p)]PF6 [terpy-C6H4Cl-p=4'-(4-chlorophenyl)-2,2':6',2''-terpyridine, (1)], and [Ir(ptpy)(2)(kappa N-2-terpy-Cl)]PF6 [terpy-Cl=4'-chloro-2,2':6',2''-terpyridine, (2);ptpy=2-(p-tolyl)pyridinato)] are described. The molecular structures of compounds 1 and 2 in the crystal were determined by single-crystal X-ray diffraction. 1 crystallized from dichloromethane/methanol/iso-hexane in the monoclinic space group P2/(n) and 2 from the same mixture of solvents in the triclinic space group P(-)1. Photophysical investigations on 1 and 2 revealed broad unstructured luminescence in the red spectral region with the emission maxima in dichloromethane at 620 and 630 nm respectively. To explore cytotoxic properties of compounds 1 and 2, a colorimetric assay (MTT assay) against prominent cancer cell lines, MCF-7 and HT-29, was performed. The determined IC50 values are in the low micromolar range (2-3 mu M). In comparison to cisplatin, the tested complexes 1 and 2 exhibit up to >20-fold (MCF-7) and >40-fold (HT-29) increase in biological activity

Synthesis, structure and photophysical properties of binuclear methylplatinum complexes containing cyclometalating 2-phenylpyridine or benzo{h}quinoline ligands: a comparison of intramolecular Pt–Pt and π–π interactions

The binuclear cyclometalated complexes [Pt2Me2(ppy)2(μ-dppm)], 1a, and [Pt2Me2(bhq)2(μ-dppm)], 1b, in which ppy = 2-phenylpyridyl, bhq = benzo{h}quinoline and dppm = bis(diphenylphosphino)methane, were synthesized by the reaction of [PtMe(SMe2)(ppy)] or [PtMe(SMe2)(bhq)] with 1/2 equiv of dppm at room temperature, respectively. Complexes 1a and 1b were fully characterized by multinuclear (1H, 31P, 13C, and 195Pt) NMR spectroscopy and were further identified by single crystal X-ray structure determination. A comparison of the intramolecular Pt–Pt and π–π interactions in complexes 1a and 1b has been made on the basis of data on crystal structures and wave functions analysis. The binuclear complexes 1a and 1b are luminescent in the solid state, and showing relatively intense orange–red emissions stemming from 3MMLCT excited states. The reaction of complex 1b with excess MeI gave the binuclear cyclometalated Pt(IV)–Pt(IV) complex [Pt2Me4(bhq)2(μ-I)2], 2. Crystal structure of complex 2 shows intermolecular C–H⋯I and C–H⋯π interactions in solid state

Construction and performance of OLED devices prepared from liquid-crystalline TADF materials

The device performance is reported for three compounds which show both thermally activated delayed fluorescence and liquid crystallinity, and use the donor 3,6-bis(3,4-didodecyloxyphenyl)carbazole. Two of the compounds, whose photophysics were reported previously, are based on a terephthalonitrile acceptor. A third and new compound is based on an isophthalonitrile acceptor and shows a more temperature-accessible mesophase and enhanced solution emission quantum yield. Two of the compounds show device external quantum efficiencies of between 2-3% and exhibit very small efficiency roll off. The responses are evaluated in terms of the specific nature of the materials

Design of functionalized b-ketoenole derivatives as efficient fluorescent dyes for detection of amyloid fibrils

The self-association of proteins into insoluble filamentous aggregates - amyloid fibrils - is associated with a range of protein deposition disorders. With the aim of developing fluorescent probes sensitive to amyloid aggregates, a new series of derivatives of (2Z,5Z,7E)-6-hydroxy-2-(alkylamino)-8-arylocta-2,5,7-trien-4-one dyes was synthesized. These dyes are less sensitive to native amyloidogenic proteins, such as insulin or lysozyme, while they have the ability to exhibit a pronounced fluorescence response in the presence of amyloid fibrils of these proteins depending on the structure of the dye tail groups. The dyes associated with the fibrils show green-yellow emission (495-540 nm) and rather large Stokes shift values (68-125 nm). Upon binding to the fibrils, the fluorescence quantum yields of the dyes could increase by a hundred times up to 0.18-0.47, and the fluorescence intensity decay time strongly enhances up to 0.9-1.3 ns. These features make ketoenoles attractive as probes for the detection of amyloid fibrils; besides, the efficiency of these dyes for real-time monitoring of the kinetics of protein aggregation is shown. The best sensing properties were shown by dyes 2 and 9 bearing short amino tail groups (correspondingly 2-methoxyethyl and 2-hydroxyethyl) and a 4-substituted phenyl moiety at the other end of the ketoenole backbone

Luminescent gold–silver complexes derived from neutral bis(perfluoroaryl)diphosphine gold(I) precursors

Complex [Au{4-C6F4(4-C6BrF4)}(tht)] reacts with diphosphines (L–L) such as bis(diphenylphosphino)methane (dppm) or 1,2-bis(diphenylphosphino)benzene (dppb) in a 2 : 1 molar ratio in dichloromethane, leading to neutral products of stoichiometry [(Au{4-C6F4(4-C6BrF4)})2(μ-L–L)] (L–L = dppm (1), dppb (2)). In the crystal structure of complex 2 short Au⋯Au interactions of 2.9367(5) and 2.9521(5) Å appear. This complex displays an orange emission, which is assigned to arise from a charge transfer transition from a metal centered Au–Au orbital to an orbital located at the diphosphine ligand. Addition of silver trifluoroacetate to these complexes in a 1 : 1 or a 2 : 1 molar ratio generates polymeric heterometallic gold–silver compounds of stoichiometry [Ag2Au2{4-C6F4(4-C6BrF4)}2(CF3CO2)2(μ-L–L)]n (L–L = dppm (3), dppb (4)), which confirms the capability of the neutral [(Au{4-C6F4(4-C6BrF4)})2(μ-diphosphine)] units to act as electron density donors when treated with a Lewis acid substrate. These heterometallic derivatives show blue emissions indicating large HOMO–LUMO band gaps, due to the stabilization that the gold-based HOMO orbitals suffer when the electron withdrawing silver trifluoroacetate fragments interact with them

Eliminating the Reverse ISC Bottleneck of TADF Through Excited State Engineering and Environment‐Tuning Toward State Resonance Leading to Mono‐Exponential Sub‐µs Decay. High OLED External Quantum Efficiency Confirms Efficient Exciton Harvesting

The electronic structure and photophysics of the recently designed organic direct singlet harvesting (DSH) molecule are explored, in which donor (D) and acceptor (A) are held at distance by two bridges. One of the bridges is functionalized with fluorene. This structure leads to an ultrasmall singlet–triplet energy gap of ∆E (S1−T1) ≈ 10 cm−1 (≈1 meV) between the charge transfer states 1,3CT and shows an energetically close-lying 3ππ* state localized on fluorene. Dielectric constant variation of the environment leads to state crossing of 3ππ* and 1,3CT near ε = 2.38 (toluene), as confirmed through time-dependent density functional theory (DFT) and state-specific DFT/polarizable continuum model excited-state calculations. Transient absorption (TA) and time-resolved luminescence in the femtosecond to microsecond regimes show rates of intersystem crossing (ISC) and reverse ISC (rISC) of >109 s–1. Thus, a strictly mono-exponential short-lived photo-luminescence decay (431 ns) is observed, revealing that rISC is no longer the bottleneck responsible for long thermally activated delayed fluorescence. Ultrafast TA displays a time constant of ≈700 fs, representing the relaxation time of DSH and its solvent environment to the relaxed 1CT state with a molecular dipole moment of ≈40 D. Importantly, OLED devices, emitting sky-blue light and showing high external quantum efficiency of 19%, confirm that singlet and triplet excitons are harvested efficiently

Design strategies for materials showing thermally activated delayed fluorescence and beyond: Towards the fourth-generation OLED mechanism

Design strategies for molecules showing thermally activated delayed fluorescence (TADF) are discussed, and a new emitter concept based on an almost zero-energy-gap is developed. Thermal activation is not substantial. Applied in an organic light emitting diode, all singlet and triplet excitons are harvested directly in the lowest singlet state without time-delaying TADF. This landmarking mechanism, being beyond TADF, leads to emission decay times in the sub-s range

Temperature dependence of photophysical properties of a dinuclear C^N-cyclometalated Pt(ii) complex with an intimate Pt–Pt contact. Zero-field splitting and sub-state decay rates of the lowest triplet

The temperature dependence (1.7 K < T < 100 K) of emission decay is reported for the first time for a type of di-nuclear Pt complex featuring a metal-metal-to-ligand charge transfer (MMLCT) lowest energy transition that arises from a strong Pt-Pt interaction. The effect of local variation of the host/guest cage in a polymer matrix upon the phosphorescence decay time constants is characterized by the Kohlrausch-Williams-Watts function. The temperature dependence of the average decay time constants is fit by a Boltzmann-type expression to obtain the average zero-field splittings and individual sublevel decay rates of the photoluminescent triplet excited state