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We report the annulation of heterocyclic building blocks to access π-extended polycyclic aromatic hydrocarbons (PAHs). The method involves the trapping of short-lived hetarynes with catalytically-generated biaryl palladium intermediates and allows for the concise appendage of three or more fused aromatic rings about a central heterocyclic building block. Our studies focus on annulating the indole and carbazole heterocycles through the use of indolyne and carbazolyne chemistry, respectively, the latter of which required the synthesis of a new carbazolyne precursor. Notably, these represent rare examples of transition metal-catalyzed reactions of N-containing hetarynes. We demonstrate the utility of our methodology in the synthesis of heterocyclic π-extended PAHs, which were then applied as ligands in two-coordinate metal complexes. As a result of these studies, we identified a new thermally-activated delayed fluorescence (TADF) emitter that displays up to 81% photoluminescence efficiency, along with insight into structure-property relationships. These studies underscore the utility of heterocyclic strained intermediates in the synthesis and study of organic materials.

Two‐coordinate carbene Cu(Ι) amide complexes with sterically bulky groups such as the diisopropyl phenyl (dipp) on the carbenes have been shown to have comparable performance to the phosphorescent emitters bearing heavy atoms such as iridium and platinum. These bulky groups enforce a coplanar molecular structure and suppress the nonradiative decay rates. Here, three different two‐coordinate Cu(Ι) complexes were investigated that bear a common thiazole carbene, 3‐(2,6‐diisopropylphenyl)‐4,5‐dimethylthiazol‐2‐ylidene, with only a single dipp group, and carbazolyl ligands with substituents of varying steric bulk ortho to N. These substituents have a negligible impact on luminescence energies of the complexes but serve to modulate the rotation barriers along the metal–ligand coordinate bond. The geometric arrangement of ligands (syn‐ or anti‐conformer) in complexes with alkyl substituents were found to differ, being syn in the solid state versus anti in solution as revealed by crystallographic analysis and nuclear magnetic resonance spectroscopy. In addition, calculations were performed to determine potential energy surfaces for different conformations of the three complexes to provide a theoretical evaluation of rotation barriers around the metal–ligand bond axis. The relationship between rotation barriers and photophysical properties demonstrate that rates for nonradiative decay decrease with increasing bulk of the substituents on the carbazolyl ligand. [ABSTRACT FROM AUTHOR]

The photoluminescence properties of organic–inorganic pyridinium lead bromide [(pyH)PbBr3] and iodide [(pyH)PbI3] compounds were investigated as a function of temperature. The inorganic substructure consists of face-sharing chains of PbX6 octahedra. Diffuse reflectance spectra of the compounds show low energy absorption features consistent with charge transfer transitions from the PbX3 chains to the pyridinium cations. Both compounds display extremely weak luminescence at room temperature that becomes strongly enhanced upon cooling to 77 K. Broad, featureless low energy emission (λem > 600 nm) in both compounds have large Stokes shifts [1.1 eV for (pyH)PbBr3 and 0.46 eV for (pyH)PbI3] and are assigned to transitions from self-trapped excitons on the inorganic chains whereas emission at higher energy in (pyH)PbBr3 (λem = 450 nm) is assigned to luminescence from a free exciton state. Analysis of data from temperature-dependent luminescence intensity measurements gives activation energies (Ea) for non-radiative decay of the self-trapped excitons in (pyH)PbBr3 and (pyH)PbI3, (Ea = 0.077 eV and 0.103 eV, respectively) and for the free exciton in (pyH)PbBr3 (Ea = 0.010 eV). Analysis of temperature dependent luminescence lifetime data indicates another non-radiative decay process in (pyH)PbI3 at higher temperatures (Ea = 0.17 eV). A large increase in the luminescence lifetime of (pyH)PbI3 below 80 K is consistent with thermalization between triplet sublevels. Analysis of the luminescence power dependence for (pyH)PbI3 shows superlinear response suggestive of quenching by static traps. [ABSTRACT FROM AUTHOR]

This study presents the synthesis and characterization of two spirobifluorenyl derivatives substituted with either triphenylmethyl (SB-C) or triphenylsilyl (SB-Si) moieties for use as host materials in phosphorescent organic light-emitting diodes (PHOLED). Both molecules have similar high triplet energies and large energy gaps. Blue Ir(tpz)3 and green Ir(ppy)3 phosphorescent devices were fabricated using these materials as hosts. Surprisingly, SB-Si demonstrated superior charge-transporting ability compared to SB-C, despite having similar energies for their valence orbitals. In particular, SB-Si proved to be a highly effective host for both blue and green devices, resulting in maximum efficiencies of 12.6% for the Ir(tpz)3 device and 9.6% for the Ir(ppy)3 device. These results highlight the benefits of appending the triphenylsilyl moiety onto host materials and underscore the importance of considering the morphology of hosts in the design of efficient PHOLEDs. [ABSTRACT FROM AUTHOR]

The dynamic photoluminescence properties, and potential quenching mechanisms, of anti-B18H22, 4,4′-Br2-anti-B18H20, and 4,4′-I2-anti-B18H20 are investigated in solution and polymer films. UV stability studies of the neat powders show no decomposition occurring after intense 7 day light soaking. In contrast, clusters incorporated into polymer films are found to degrade into smaller borane fragments under the same irradiation conditions. To highlight the utility of these compounds, we leverage their favorable optical properties in a prototype UV imaging setup. [ABSTRACT FROM AUTHOR]

Studies were conducted to explore the electronic properties of the cyclometalated (C^N) complexes of iridium and platinum metals with catechol ligand. The complexes were observed to exhibit a reversible reduction of the semiquinone form to the catechol form of the ligand and an irreversible oxidation to the unstable quinone form of the ligand.

A series of cationic bis-cyclometalated iridium(III) complexes are synthesized and their electrochemical, photophysical, electroluminescent properties are studied. The complexes are found to be luminescent both in a fluid solution and as neat solids at 298 K, while single-layer electroluminescent devices that give blue, green, and red electroluminescence are also fabricated.

The approaches are reported to achieve efficient blue to near-UV emission from triscyclometalated iridium(III) materials. The approach to tuning the photophysical properties of cyclometalated Ir complexes investigated in the study involved the control of the relative energies of emissive and non-emissive excited states.

The synthesis and photophysical characterization of a series of (N,C(super 2')-(2-para-tolylpyridyl)2Ir(LL') [tpy)2Ir(LL')] (LL' = 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tert-butylisocyanide (CN-t-Bu) are reported. The electrochemical and photophysical properties of the (typ)2Ir(LL') complexes are discussed in detail.

Molecular dynamics are used to investigate the instantaneous structure of a fourth generation dendimer of propolene amine dissolved in CH2Cl2, and the same system upon the subsequent encapsulation of several eosin dyes. Calculations in a cubic box with upto `3500 solvent molecules and maximum of 12 eosins show that one of the effects of the presence of the guest molecules is to 'close' the structure of the box where they are contained.

The methods for tris-cyclometalates are reported, which demonstrate that controlling the reaction conditions could impart significant control in product configuration. For all the cyclometalating ligands studied, there is a preference to form the facial isomers at high temperatures and the meridional isomers at lower temperatures.

A series of twelve two-coordinate coinage metal, Cu, Ag and Au, complexes with carbene-metal-amide structures were prepared. The complexes all display thermal assisted delayed fluorescence (TADF) emission at room temperature from interligand charge transfer (ICT) excited state with short lifetimes (less than 2 μs) and photoluminescent quantum yields that reach near unity. Owing to the involvement of the substituents in the emissive transitions and different metal ion volume, the natural transition orbital (NTO) overlap of the emissive state can be adjusted in a wide range from 0.21 to 0.41. Investigations on the relationship between the NTO overlap of the emissive state and key TADF photophysical properties demonstrated that both singlet–triplet energy gap and radiative decay rate of S1 state increase along with the NTO overlap exponentially. Consequently, the overall TADF radiative decay rate leads to a maximum when plotted against the NTO overlap, giving the ideal zone from 0.25 to 0.30 for high TADF radiative decay rate in this class of two-coordinate coinage metal complex luminophores. [ABSTRACT FROM AUTHOR]

Research has been conducted on the square planar platinum complexes. The synthesis, photolysis and electrochemistry of these cyclometalated complexes have been investigated and the details are presented.

Wide energy gap materials dispiro[fluorene‐9,9′‐anthracene‐10′,9″‐fluorene] (SAS) and dispiro[xanthene‐9,9′‐anthracene‐10′,9″‐xanthene] (XAX) containing double spiro–carbons, are introduced as hosts for blue phosphorescent organic light‐emitting diodes (PHOLEDs). Both SAS and XAX are free of heteroatomic exocyclic bonds, which are implicated in limiting the stability of blue PHOLEDs. The materials are synthesized in gram‐scale quantities through short and efficient paths. They have large energy gaps (≥5.0 eV) between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and correspondingly have high triplet energies in solid state (ET ≈ 3.0 eV). Analysis of devices using SAS and XAX as host materials with the blue phosphorescent dopant fac‐tris(N,N‐di‐p‐tolyl‐pyrizinoimidazol‐2‐yl)iridium(III) (Ir(tpz)3), shows that charges are transported and trapped by the dopant, which subsequently forms excitons directly on the phosphor. As a result, luminescence quenching pathways are suppressed which leads to blue phosphorescent devices with high (≈18%) external quantum efficiency. Thus, SAS and XAX serve as promising host materials, with high triplet energies suitable for blue PHOLEDs. [ABSTRACT FROM AUTHOR]

A series of substituted aza‐boron‐dipyridylmethene (aD) compounds are demonstrated as fluorescent dopant emitters in blue organic light emitting diodes (OLEDs). Replacing the meso‐carbon of a dipyridylmethene dye with nitrogen to form the aD chromophore leads to a destabilization of the highest occupied molecular orbital in aD, as evidenced both from their experimentally determined photophysical and electrochemical properties. These properties are consistent with theoretical calculations of the molecular energetics. These aD derivatives emit violet to blue light, peaking between 400 and 460 nm with photoluminescent quantum yields over 85%. The aD compounds have small energy differences (<400 meV) between their singlet and triplet excited states. OLEDs fabricated with an aza‐boron‐dipyridylmethene emitting fluorophore give an external quantum efficiency of 4.5% on glass substrates, close to the theoretical maximum for fluorescent OLEDs. [ABSTRACT FROM AUTHOR]

The photophysical and electrochemical properties of N‐heterocyclic carbene complexes of Iridium (III) (Ir(C^C:)3, where C^C: = N‐phenyl,N‐methyl‐pyrazinoimidazol‐2‐yl (pmpz), N,N‐di‐p‐tolyl‐pyrazinoimidazol‐2‐yl (tpz)) are reported. Facial and meridional isomers of Ir(pmpz)3 are prepared, but only the facial isomer can be isolated for Ir(tpz)3. The fac‐Ir(pmpz)3 and fac‐Ir(tpz)3 complexes have emission maxima at 465 nm in polystyrene, whereas the emission maximum of mer‐Ir(pmpz)3 is redshifted to 495 nm. The emission energies and photoluminescent quantum yield (ΦPL) in solution decrease on going from nonpolar to polar solvents; however, all the complexes are efficient emitters in polystyrene at room temperature (ΦPL = 88–96%) and 77 K. Blue phosphorescent organic light emitting diodes employing fac‐Ir(tpz)3 as an emissive dopant achieves a high external electroluminescence efficiency (≈18 ± 1%) and brightness (29 000 cd m−2) at low current density. [ABSTRACT FROM AUTHOR]

A luminescent bimetallic AuI complex comprised of N‐heterocyclic carbene (NHC) and carbazole (Cz) ligands, that is, (NHC')Au(NHC)AuCz has been synthesized and studied. Both carbene ligands in the bimetallic complex act as electron acceptors in tandem to increase the energy separation between the ground and excited state, which is higher than those found in either monometallic analogue, (NHC)AuCz and (NHC')AuCz. A coplanar geometry designed into the tandem complex ensures sufficient electronic coupling between the π‐orbitals of the ligands to impart a strong oscillator strength to the singlet intra‐ligand charge‐transfer (1ICT) transition. Theoretical modelling indicates that the emissive ICT excited state involves both NHC ligands. The tandem complex gives blue luminescence (λmax=480 nm) with a high photoluminescent quantum yield (ΦPL=0.80) with a short decay lifetime (τ=0.52 μs). Temperature‐dependent photophysical studies indicate that emission is via thermally assisted delayed fluorescence (TADF) and give a small singlet‐triplet energy difference (ΔEST=50 meV, 400 cm−1) consistent with the short TADF lifetime. [ABSTRACT FROM AUTHOR]

Bromination of the luminescent borane, anti-B18H22, via electrophilic substitution using AlCl3 and Br2, yields the monosubstituted derivative 4-Br-anti-B18H21 as an air-stable crystalline solid. In contrast to the unsubstituted parent compound, 4-Br-anti-B18H21 possesses dual emission upon excitation with UV light and exhibits fluorescence at 410 nm and phosphorescence at 503 nm, with Φtotal = 0.07 in oxygen-free cyclohexane. Increased oxygen content in cyclohexane solution quenches the phosphorescence signal. The fluorescent signal intensity remains unaffected by oxygen, suggesting that this molecule could be used as a ratiometric oxygen probe. [ABSTRACT FROM AUTHOR]

Several new iridium based cyclometalated complexes were investigated as phosphorescent dopants for molecularly doped polymeric organic light-emitting diodes. Specifically, the complexes used in this study were iridium (III) bis(2-phenylpyridinato-N,C[sup 2']) (acetylacetonate) [ppy], iridium (III) bis(7,8-benzoquinolinato-N,C[sup 3']) (acetylacetonate) [bzq], iridium (III) bis(2-phenylbenzothiazolato-N,C[sup 2']) (acetylacetonate) [bt], iridium (III) bis(2-(2&prime-; naphthyl)benzothiazolato-N, C[sup 2']) (acetylacetonate) [bsn] and iridium (III) bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C[sup 3']) (acetylacetonate) [btp]. Single layer devices of doped polyvinylcarbazole: 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole give maximum external quantum efficiencies that varied from 3.5% for the ppy dopant to 0.4% for the btp dopant. Several different device heterostructure architectures were explored, and the best quantum efficiency of the devices reached 4.2% for the heterostructures. [ABSTRACT FROM AUTHOR]

A series of five platinum(II) complexes are described that have illustrated benzannulation of aromatic molecules, which is used to blue or red-shift absorption and emission bands. The studies have shown that either a blue shift or a red shift in absorption and emission maxima, relative to their respective nonbenzannulated compounds is observed for this series of molecules that has depended on the site of benzannulation.

The photofragmentation of (3-Me-4',6'-dfppy)Pt(dpm) (dfppy = difluorophenylpyridinato; dpm = dipivaloylmethyl or 2,2,6,6-tetramethyl-3,5-heptanedionato-O,O) in a molecular beam is described. The (3-Me,4',6'-dfppy) ligand has remained intact and coordinated to platinum, but coordinated (dpm) has successively broken apart.

The most efficient organic light-emitting diodes (OLEDs) are built from multiple organic layers. Arylamines are used in a high percentage of small-molecule-based devices. The properties of the OLEDs and the mechanism of device failure are discussed.