Dilute CH2Cl2 Research Articles

True- to Sky-Blue Emitters Bearing the Thiazolo[5,4-d]thiazole Electron Acceptor for Single and Tandem Organic Light-Emitting Diodes

A series of emitters displaying efficient photoluminescence (PL) and electroluminescence (EL) into the true- to sky-blue regions is herein described and employed as electroluminescent materials for the fabrication of efficient blue organic light-emitting diodes (OLEDs). The compounds possess linear, yet a twisted, donor−π–acceptor−π–donor (D−π–A−π–D) architecture, where D and A are a (substituted) carbazole (Cz) and thiazolo[5,4-d]thiazole (TzTz) moiety as the electron donor and accepting unit, respectively. D = 9H-carbazol-9-yl and 3,6-di-tert-butyl-9H-carbazol-9-yl for compounds TzTz-PCz2 and TzTz-PtbCz2, respectively. In dilute CH2Cl2 solutions, both compounds display intense (PL quantum yield = 60–74%) and short-lived (τ = ca. 0.8–2.0 ns) luminescence arising from an intramolecular charge-transfer (1ICT) excited state and falling into the sky-blue to the greenish-blue region (λem = 448–502 nm). Compared to the previously reported TzTz-TPA parental emitters that features two triphenylamine (TPA) donor groups, the highly twisted nature and less extended π-conjugation of the donor–acceptor TzTz-PCz2 and TzTz-PtbCz2 counterparts herein presented enable to widen the HOMO–LUMO energy gaps and warrant blue shifting of the emission. Finally, OLED devices fabricated by employing the herein proposed emitters are presented as well with both single- and tandem-device architectures. The so-prepared OLEDs display true-blue to sky-blue EL peaking at λEL,max = 460 nm (TzTz-PCz2) and 467–470 nm (TzTz-PtbCz2) and achieve maximum external quantum efficiency and luminance of 10.2% and 44,851 cd m–2 (for TzTz-PtbCz2) in the case of a tandem device, respectively, with a mitigated roll-off efficiency. These results demonstrate that the tandem device employing these TzTz donor–acceptor blue emitters raises the feasibility of fluorescent compounds to compete with other potential emitters in practical applications.

Synthesis and the Effect of Anions on the Spectroscopy and Electrochemistry of Mono(dimethyl sulfoxide)-Ligated Cobalt Corroles.

A new series of cobalt A3-triarylcorroles were synthesized and the compounds examined as to their electrochemical and spectroscopic properties in CH2Cl2 or dimethyl sulfoxide (DMSO) containing 10 different anions added to the solution in the form of tetrabutylammonium salts. The investigated anions were PF6-, BF4-, HSO4-, ClO4-, Br-, I-, Cl-, OAc-, F-, OTs-, and CN-, all but three of which were found to facilitate reduction of the cobalt corrole in dilute CH2Cl2 solutions, as determined by a combination of UV-vis spectroscopy and spectroelectrochemistry. The synthesized corroles are represented as (Ar)3CorCo(DMSO), where Ar is a meso-phenyl group containing one of 10 different electron-donating or -withdrawing substituents. The axial DMSO ligand was found to dissociate in dilute (10-5 M) CH2Cl2 solutions, but this was not the case at the higher electrochemical concentration of 10-3 M, where the investigated corroles exhibit a rich redox reactivity, undergoing up to five reversible one-electron-transfer reactions under the different solution conditions. The reversible half-wave potentials for generation of the singly oxidized corroles varied by over 1.0 V with a change in the electron-donating or -withdrawing meso-phenyl substituents and type of anion added to the solution, ranging from E1/2 = 0.83 V in one extreme to -0.42 V in the other. Much smaller shifts in the potentials (on the order of ∼210 mV) were observed for the reversible first reduction as a function of changes of the anion and/or corrole substituents, with the only exception being in the case of CN-, where the E1/2 values in CH2Cl2 ranged from +0.08 V in solutions containing 0.1 M TBAClO4 to >-1.8 V upon the addition of CN-.

Effects of substituents on silicon atoms upon absorption and fluorescence properties of 1,3,6,8-tetrakis(silylethynyl)pyrenes

Synthesis, UV–vis absorption, and fluorescence spectroscopic properties of 1,3,6,8-tetrakis(silylethynyl)pyrenes 2–10 were studied. Absorption maxima of CH2Cl2 solutions of these compounds appeared at 437–445 nm, and molar absorption coefficients (ε) of most of these compounds exceeded 105 L mol−1 cm−1. Fluorescence emissions measured in dilute CH2Cl2 solutions are observed in visible region, and their intensities remarkably increased compared with that of pyrene. Fluorescence spectra obtained from concentrated CH2Cl2 solutions exhibited broad excimer emissions when steric bulk of substituents on silicon atoms is sufficiently low. Molecular orbital calculations indicated that HOMO-LUMO energy gap decreased with increasing the number of phenyl groups on silicon atoms, and that the silyl groups act as electron-donating groups to tetraethynylpyrene core. Resonances in 29Si NMR spectra shifts to upfield with increasing the number of phenyl groups on silicon atoms due to the shielding effect of phenyl groups.

Coordination-Driven Dimerization of Zinc Chlorophyll Derivatives Possessing a Dialkylamino Group.

Zinc chlorophyll derivatives Zn-1-3 possessing a tertiary amino group at the C31 position have been synthesized through reductive amination of methyl pyropheophorbide-d obtained from naturally occurring chlorophyll-a. In a dilute CH2 Cl2 solution as well as in a dilute 10 %(v/v) CH2 Cl2 /hexane solution, Zn-1 possessing a dimethylamino group at the C31 position showed red-shifted UV/Vis absorption and intensified exciton-coupling circular dichroism (CD) spectra at room temperature owing to its dimer formation via coordination to the central zinc by the 31 -N atom of the dimethylamino group. However, Zn-2/3 bearing 31 -ethylmethylamino/diethylamino groups did not. The difference was dependent on the steric factor of the substituents in the tertiary amino group, where an increase of the carbon numbers on the N atom reduced the intermolecular N⋅⋅⋅Zn coordination. UV/Vis, CD, and 1 H NMR spectroscopic analyses including DOSY measurements revealed that Zn-1 formed closed-type dimers via an opened dimer by single-to-double axial coordination with an increase in concentration and a temperature decrease in CH2 Cl2 , while Zn-2/3 gave open and flexible dimers in a concentrated CH2 Cl2 solution at low temperature. The supramolecular closed dimer structures of Zn-1 were estimated by molecular modelling calculations, which showed these structures were promising models for the chlorophyll dimer in a photosynthetic reaction center.

Thienyl Difluoroboron β-Diketonates in Solution and Polylactide Media.

Difluoroboron β-diketonates have impressive optical properties in both solution and the solid state. In particular, both fluorescence and room-temperature phosphorescence are present when the dyes are confined to a rigid matrix, such as poly(lactic acid) (PLA). To expand current knowledge and color range capabilities of this unique type of multi-emitting chromophore, a series of thienyl-substituted BF2bdk complexes have been synthesized. The photophysical properties were investigated in methylene chloride solution and in the solid state as dye/PLA blends. By varying donor ability, i.e. methyl, phenyl, methoxyl, and thienyl substituents, and by changing the dye loading in the PLA media (0.1-10% dye loading) red-shifted emission was achieved, important for biological imaging applications. In dilute CH2Cl2 solution, complexes exhibited absorptions ranging from 350 - 420 nm, solid-state fluorescence in PLA ranging from 390 - 500 nm, and oxygen sensitive phosphorescence ranging from 540 - 585 nm in PLA blends. Promising candidates as dye/PLA blends serve as models for dyepolymer conjugates for application as biological oxygen nanoprobes.

Tailoring Oxygen Sensitivity with Halide Substitution in Difluoroboron Dibenzoylmethane Polylactide Materials.

The dual-emissive properties of solid-state difluoroboron β-diketonate-poly(lactic acid) (BF2bdkPLA) materials have been utilized for biological oxygen sensing. In this work, BF2dbm(X)PLA materials were synthesized, where X = H, F, Cl, Br, and I. The effects of changing the halide substituent and PLA polymer chain length on the optical properties in dilute CH2Cl2 solutions and solid-state polymer films were studied. These luminescent materials show fluorescence, phosphorescence, and lifetime tunability on the basis of molecular weight, as well as lifetime modulation via the halide substituent. Short BF2dbm(Br)PLA (6.0 kDa) and both short and long BF2dbm(I)PLA polymers (6.0 or 20.3 kDa) have fluorescence and intense phosphorescence ideal for ratiometric oxygen sensing. The lighter halide-dye polymers with hydrogen, fluorine, and chlorine substitution have longer phosphorescence lifetimes and can be utilized as ultrasensitive oxygen sensors. Photostability was also analyzed for the polymer films.

A new luminescent platinum(II) chloride complex of 6-(5-trifluoromethyl-1,2,4-triazol-3-yl)-4,4′-dimethyl-2,2′-bipyridine

Abstract A new Pt(II) chloride complex Pt(ftmbpy)Cl (1) with deprotonated 6-(5-trifluoromethyl-1,2,4-triazol-3-yl)-4,4′-dimethyl-2,2′-bipyridine terdentate ligand has been synthesized and characterized. Complex 1 gives a distorted square-planar configuration with a mono-anionic chelate ftmbpy, and displays a 1-D zigzag head-to-tail arrangement along the b axis formed via intermolecular π⋯π stacking and Pt⋯Pt interactions. A relatively weak broad absorption is observed at 360–435 nm in dilute CH2Cl2 solution at room temperature, tentatively ascribed to metal-to-ligand charge transfer (1MLCT) excited state with some mixing of intra-ligand 1ππ* character inside ftmbpy, as supported by TD-DFT analysis. It is demonstrated that complex 1 is emissive in both solution and solid states and exhibits the concentration-dependent luminescence properties originating from intermolecular Pt⋯Pt and π⋯π interactions, and the introduction of substituents (e.g. two methyl groups) into the 2,2′-bipyridyl ring is effective for improving the solubility of Pt(II) complexes.

Aerobic and Hydrolytic Decomposition of Pseudotetrahedral Nickel Phenolate Complexes

Pseudotetrahedral nickel(II) phenolate complexes Tp(R,Me)Ni-OAr (Tp(R,Me) = hydrotris(3-R-5-methylpyrazol-1-yl)borate; R = Ph {1a}, Me {1b}; OAr = O-2,6-(i)Pr(2)C(6)H(3)) were synthesized as models for nickel-substituted copper amine oxidase apoenzyme, which utilizes an N(3)O (i.e., His(3)Tyr) donor set to activate O(2) within its active site for oxidative modification of the tyrosine residue. The bioinspired synthetic complexes 1a,b are stable in dilute CH(2)Cl(2) solutions under dry anaerobic conditions, but they decompose readily upon exposure to O(2) and H(2)O. Aerobic decomposition of 1a yields a range of organic products consistent with formation of phenoxyl radical, including 2,6-diisopropyl-1,4-benzoquinone, 3,5,3',5'-tetraisopropyl-4,4'-diphenodihydroquinone, and 3,5,3',5'-tetraisopropyl-4,4'-diphenoquinone, which requires concurrent O(2) reduction. The dimeric product complex di[hydro{bis(3-phenyl-5-methylpyrazol-1-yl)(3-ortho-phenolato-5-methylpyrazol-1-yl)borato}nickel(II)] (2) was obtained by ortho C-H bond hydroxylation of a 3-phenyl ligand substituent on 1a. In contrast, aerobic decomposition of 1b yields a dimeric complex [Tp(Me,Me)Ni](2)(μ-CO(3)) (3) with unmodified ligands. However, a unique organic product was recovered, assigned as 3,4-dihydro-3,4-dihydroxy-2,6-diisopropylcyclohex-5-enone on the basis of (1)H NMR spectroscopy, which is consistent with dihydroxylation (i.e., addition of H(2)O(2)) across the meta and para positions of the phenol ring. Initial hydrolysis of 1b yields free phenol and the known complex [Tp(Me,Me)Ni(μ-OH)](2), while hydrolysis of 1a yields an uncharacterized intermediate, which subsequently rearranges to the new sandwich complex [(Tp(Ph,Me))(2)Ni] (4). Autoxidation of the released phenol under O(2) was observed, but the reaction was slow and incomplete. However, both 4 and the in situ hydrolysis intermediate derived from 1a react with added H(2)O(2) to form 2. A mechanistic scheme is proposed to account for the observed product formation by convergent oxygenation and hydrolytic autoxidation pathways, and hypothetical complex intermediates along the former were modeled by DFT calculations. All new complexes (i.e., 1a,b and 2-4) were fully characterized by FTIR, (1)H NMR, and UV-vis-NIR spectroscopy and by X-ray crystallography.

Photophysical and self-assembly properties of asymmetrical multi-aralkyl and arylaldehyde substituted pyrene derivatives

A series of novel asymmetrical pyrene derivatives with aralkyl and aldehyde groups have been successfully synthesized, and their spectroscopic parameters were investigated detailedly. The effects of aralkyl substituent amounts on the electronic absorption and emission spectra have been explored in evaluation of their potential as optical materials components. Moreover, the electrochemical properties of the new pyrene derivatives have been studied for the molecules' HOMO and LUMO levels by cyclic voltammograms. In particular, titration of anhydrous ethanol into dilute CH2Cl2 solution of above compounds, an unusual change of the fluorescence value was observed. The change is believed to correlate strongly to intermolecular charge transfer. The morphological evolution of self-assembled pyrene derivatives with (arylethynyl)aldehyde substituents, from tamen-distinct-like morphologies to vesicular textures, was obtained by increasing aralkyl-substituted fragments. These asymmetrical discotic compounds represent an interesting set of candidates for optoelectronic device components.

Solution and Thin‐Film Aggregation Studies of Octasubstituted Dendritic Phthalocyanines

AbstractThe synthesis and solution and thin‐film characterization of eight octasubstituted dendritic phthalocyanines (Pcs) and their zinc complexes are reported. The Pc chromophore was substituted in the 2,3,9,10,16,17,23,24‐positions with three generations of benzylaryl ether dendrons with either a benzyl (3a‐3c) or 3,5‐di‐t‐butylbenzyl periphery (3d‐3f). Visible spectra in solution (CH2Cl2‐EtOH mixtures, toluene, THF, dioxane, acetone, and EtOAc) indicated a varying degree of chromophore aggregation that depended on solvent, dendrimer generation, and whether the Pc was metallated. Variable‐concentration visible spectroscopic studies were analyzed using a nonlinear least‐squares fitting procedure giving Kd values. These values further quantitated the observations that the t‐butyl‐substituted den‐drimers 3d‐3f were all less prone to aggregation in solution than the unsubstituted dendrimers 3a‐3c, with a monotonic decrease in Kd across the series 3a → 3b → 3c → 3d → 3e → 3f. Second‐generation t‐butyl‐substituted dendrimer 3f showed little to no aggregation in all solvents studied. Thin‐film studies indicated that the largest members of the two dendrimer groups, third‐generation 3c and second‐generation 3f, were largely monomeric as evidenced by split Q‐bands, similar to that seen in dilute CH2Cl2 solution when deposited via spin‐coating onto glass slides. The metallated zinc Pcs 4a‐4f all exhibited significantly less tendency toward aggregation in both solution and thin‐films than their unmetallated analogues.

Anthracene‐Cored Dendrimer for Solution‐Processible Blue Emitter: Syntheses, Characterizations, Photoluminescence, and Electroluminescence

AbstractSummary: A second‐generation blue fluorescent anthracene‐cored dendrimer EH‐G2AN was readily synthesized via a convergent method. Its monodispersity was confirmed by 1H NMR and MALDI‐TOF mass measurement. The peak emission of EH‐G2AN in a dilute CH2Cl2 solution was observed at 416 nm with a shoulder at 434 nm and moved to 418 nm in the solid film with the shoulder at 433 nm. The nearly “perfect” overlap of solution and solid emission spectra revealed the absence of molecular aggregations in the solid film, which was apparently suppressed by the presence of rigid and bulky 1,3,5‐phenylene‐based dendrons and 2‐ethylhexyloxy solubilizing peripheral groups. EH‐G2AN appeared strikingly stable with the onset decomposition temperature above 350 °C and remained at the high temperature of 428 °C where 5% weight loss occurred. The electroluminescent device [ITO/PEDOT:PSS/EH‐G2AN/Ba/Al] showed a peak emission at 442 nm and maximal external device efficiency of 0.82%@170 cd · m−2. After inserting a PVK layer between the hole injection layer and emitting layer, a maximal external device efficiency of 1.05%@184 cd · m−2 was obtained with a narrow FWHI of merely ca. 42 nm in the device configuration [ITO/PEDOT:PSS/PVK/EH‐G2AN/Ba/Al]. magnified image

Total Synthesis of Dictyodendrin B

A concise total synthesis of dictyodendrin B (1) is reported, a scarce marine alkaloid endowed with promising telomerase inhibitory activity. Key steps of the chosen route are a reductive cyclization of ketoamide 11 to indole 12 mediated by low-valent titanium (from TiCl3 and KC8) followed by a photochemical 6pi-electrocyclization, which was performed in the presence of Pd/C and nitrobenzene to effect concomitant dehydrogenation/aromatization of the product initially formed. Regioselective bromination of the resulting pyrrolocarbazole 13 followed by lithium/bromine exchange and quenching of the resulting organolithium species with p-methoxybenzaldehyde installed the side chain at C2. Oxidation of the benzylic alcohol 15 thus obtained to ketone 17 was best achieved with catalytic amounts of tetra-n-propylammonium perruthenate (TPAP) and N-methylmorpholine-N-oxide (NMO) in dilute CH2Cl2 solution to avoid the formation of undue amounts of the unsymmetrical dimer 16. Ketone 17 was elaborated into the natural product by selective cleavage of the isopropyl ether with BCl3, introduction of the sulfate moiety with the aid of trichloroethyl chlorosulfuric acid ester, deprotection of all lateral methyl ether groups, and final reductive cleavage of the trichloroethyl ester moiety. The spectroscopic data of synthetic dictyodendrin B thus formed matched those of an authentic sample in all regards. Moreover, it was shown that global deprotection of the peripheral -OH groups in pyrrolo[2,3-c]carbazole 13 is accompanied by spontaneous air-oxidation to form the quinone core of dictyodendrin C.

Synthesis of New Enantiopure Bicyclic 1,2‐Oxazines by Addition of Lithiated Methoxyallene to Chiral Cyclic Nitrones

AbstractA highly diastereoselective addition of lithiated methoxyallene 3 to chiral cyclic nitrones 1 and 2 provided N‐hydroxy pyrrolidines 4 and 5, respectively, which cyclized to bicyclic 1,2‐oxazines 6 and 7 by simple stirring in dilute CH2Cl2 solution. Storage of 4 in a more concentrated solution led to formation of a 60:40 mixture of 1,2‐oxazine 6 and amine oxide 8. Hydroboration of 7 furnished the hydroxy‐substituted bicyclic 1,2‐oxazine 9 with excellent diastereoselectivity. Hydrogenolysis of 6 provided the substituted pyrrolidine derivative 10. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Generation of Stable Radical Cations (Polarons) and Dications (Bipolarons) on Model Thiophene Oligomers

ABSTRACTOxidative doping of individual thiophene oligomers nT (n = 3 to 6) with FeC13 in dilute CH2Cl2 solution generates the corresponding radical cations (polarons) nT+.. as evidenced by in-situ visible/near infrared absorption and electron spin resonance spectroscopies. The nT+. species in solution progressively precipitate as conducting (0′300K = 10−1−10−2 S/cm) and strongly paraaagnetic radical cation salts (g = 2.003, ΔHPP ∼ 4–8 G). The conductivity of the 6T+. salt is weakly temperature dependent, with an activation energy of 32 meV above 100 K and a tendency to level Dff at lower temperatures. In the case of the sexithienyl radical 6T+., further doping results in the quantitative conversion into the dication 6T++ (bipolaron).