Solubilised bright blue-emitting iridium complexes for solution processed OLEDs

EZ-C acknowledges the University of St Andrews for financial support. IDWS and AKB acknowledge support from EPSRC (EP/J01771X). The authors would like to thank the Engineering and Physical Sciences Research Council for financial support for Adam Henwood: EPSRC DTG Grants: EP/J500549/1; EP/K503162/1; EP/L505097/1.Combining a sterically bulky, electron-deficient 2-(2,4-difluorophenyl)-4-(2,4,6- trimethylphenyl)pyridine (dFMesppy) cyclometalating C^N ligand with an electron rich, highly rigidified 1,1’-(α,α’-o-xylylene)-2,2’-biimidazole (o-xylbiim) N^N ligand gives an iridium complex, [Ir(dFMesppy)2(o-Xylbiim)](PF6), that achieves extraordinarily bright blue emission (ΦPL = 90%; λmax = 459 nm in MeCN) for a cationic iridium complex. This complex is compared with two reference complexes bearing 4,4’-di-tert-butyl-2,2’- bipyridine, and solution-processed organic light emitting diodes (OLEDs) have been fabricated from these materials.Publisher PDFPeer reviewe

Impact of ultrasound on management for dyspnea presentations in a Rwandan emergency department

Background The complexity of diagnosis for critically ill dyspnea presentations in the emergency department remains a challenge. Accurate and rapid recognition of associated life-threatening conditions is paramount for timely treatment. Point-of-care ultrasound (POCUS) has been shown to impact the diagnosis of dyspnea presentations in resource-rich settings, and may be of greater diagnostic benefit in resource-limited settings. Methods We prospectively enrolled a convenience sample of 100 patients presenting with dyspnea in the Emergency Department at University Teaching Hospital of Kigali (UTH-K) in Rwanda. After a traditional history and physical exam, the primary treating team listed their 3 main diagnoses and ranked their confidence accuracy in the leading diagnosis on a Likert scale (1–5). Multi-organ ultrasound scans performed by a separate physician sonographer assessed the heart, lungs, inferior vena cava, and evaluated for lower extremity deep vein thrombosis or features of disseminated tuberculosis. The sonographer reviewed the findings with the treating team, who then listed 3 diagnoses post-ultrasound and ranked their confidence accuracy in the leading diagnosis on a Likert scale (1–5). The hospital diagnosis at discharge was used as the standard in determining the accuracy of the pre- and post-ultrasound diagnoses. Results Of the 99 patients included in analysis, 57.6% (n = 57) were male, with a mean age of 45 years. Most of them had high-level acuity (54.5%), the dyspnea was of acute onset (45.5%) and they came from district hospitals (50.5%). The most frequent discharge diagnoses were acute decompensated heart failure (ADHF) (26.3%) and pneumonia (21.2%). Ultrasound changed the leading diagnosis in 66% of cases. The diagnostic accuracy for ADHF increased from 53.8 to 100% (p = 0.0004), from 38 to 85.7% for pneumonia (p = 0.0015), from 14.2 to 85.7% for extrapulmonary tuberculosis (p = 0.0075), respectively, pre and post-ultrasound. The overall physician diagnostic accuracy increased from 34.7 to 88.8% pre and post- ultrasound. The clinician confidence in the leading diagnosis changed from a mean of 3.5 to a mean of 4.7 (Likert scale 0–5) (p < 0.001). Conclusions In dyspneic patients presenting to this Emergency Department, ultrasound frequently changed the leading diagnosis, significantly increased clinicians’ confidence in the leading diagnoses, and improved diagnostic accuracy

Conjugated, rigidified bibenzimidazole ancillary ligands for enhanced photoluminescence quantum yields of orange/red-emitting iridium(III) complexes

EZ-C acknowledges the University of St Andrews for financial support. We thank Umicore AG for the gift of materials. We would like to thank the Engineering and Physical Sciences Research Council for financial support for E.Z-C. (EP/M02105X/1) and for the studentship of A.H. (EP/J500549/1, EP/K503162/1, EP/L505097/1). We thank the EPSRC UK National Mass Spectrometry Facility at Swansea University for analytical services. We also would like to thank EaStCHEM and the School of Chemistry for supporting the computing facilities maintained by Dr. H. Früchtl.A series of six novel [Ir(C^N)2(N^N)](PF6) complexes (C^N is one of two cyclometalating ligands: 2-phenyl-4-(2,4,6-trimethylphenyl)pyridine, MesppyH, or 2- (napthalen-1-yl)-4-(2,4,6-trimethylphenyl)pyridine, MesnpyH; N^N denotes one of four neutral diamine ligands: 4,4’-di-tert-butyl-2,2’-bipyridine, dtbubpy, 1H,1’H-2,2’- bibenzimiazole, H2bibenz, 1,1’-(α,α’-o-xylylene)-2,2’-bibenzimidazole, o-Xylbibenz or 2,2’- biquinoline, biq) were synthesised and their structural, electrochemical and photophysical properties comprehensively characterised. The more conjugated MesnpyH ligands confer a red-shift in the emission compared to MesppyH but maintain high photoluminescence quantum yields due to the steric bulk of the mesityl groups. The H2bibenz and o-Xylbibenz ligands are shown to be electronically indistinct to dtbubpy but give complexes with higher quantum yields than analogous complexes bearing dtbubpy. In particular, the rigidity of the o-Xylbibenz ligand, combined with the steric bulk of the MesnpyH C^N ligands, give a red-emitting complex 4 (λPL = 586, 623 nm) with a very high photoluminescence quantum yield (ΦPL = 44%) for an emitter in that regime of the visible spectrum. These results suggest that employing these ligands is a viable strategy for designing more efficient orange-red emitters for use in a variety of photophysical applications.PostprintPeer reviewe

N-type graphene induced by dissociative H-2 adsorption at room temperature

Studies of the interaction between hydrogen and graphene have been increasingly required due to the indispensable modulation of the electronic structure of graphene for device applications and the possibility of using graphene as a hydrogen storage material. Here, we report on the behaviour of molecular hydrogen on graphene using the gate voltage-dependent resistance of single-, bi-, and multi-layer graphene sheets as a function of H-2 gas pressure up to 24 bar from 300 K to 345 K. Upon H-2 exposure, the charge neutrality point shifts toward the negative gate voltage region, indicating n-type doping, and distinct Raman signature changes, increases in the interlayer distance of multi-layer graphene, and a decrease in the d-spacing occur, as determined by TEM. These results demonstrate the occurrence of dissociative H-2 adsorption due to the existence of vacancy defects on graphene.open12

Lessons learned in tuning the optoelectronic properties of phosphorescent iridium(III) complexes

This perspective illustrates our approach in the design of heteroleptic cationic iridium(III) complexes for optoelectronic applications, especially as emitters in electroluminescent devices. We discuss changes in the photophysical properties of the complexes as a consequence of modification of the electronics of either the cyclometalating (C^N) or the ancillary (N^N) ligands. We then broach the impact on these properties as a function of modification of the structure of both types of ligands. We explain trends in the optoelectronic behaviour of the complexes using a combination of rationally designed structure-property relationship studies and theoretical modelling that serves to inform subsequent ligand design. However, we have found cases where the design paradigms do not always hold true. Nevertheless, all these studies contribute to the lessons we have learned in the design of heteroleptic cationic phosphorescent iridium(III) complexes

Lessons learned in tuning the optoelectronic properties of phosphorescent iridium(III) complexes

EZ-C acknowledges past and present group members for their tireless efforts and enthusiasm and the University of St Andrews for financial support. The authors would like to thank the Engineering and Physical Sciences Research Council for financial support for Adam Henwood (EPSRC DTG Grants: EP/J500549/1; EP/K503162/1; EP/L505097/1)This perspective illustrates our approach in the design of heteroleptic cationic iridium(III) complexes for optoelectronic applications, especially as emitters in electroluminescent devices. We discuss changes in the photophysical properties of the complexes as a consequence of modification of the electronics of either the cyclometalating (C^N) or the ancillary (N^N) ligands. We then broach the impact on these properties as a function of modification of the structure of both types of ligands. We explain trends in the optoelectronic behaviour of the complexes using a combination of rationally designed structure-property relationship studies and theoretical modelling that serves to inform subsequent ligand design. However, we have found cases where the design paradigms do not always hold true. Nevertheless, all these studies contribute to the lessons we have learned in the design of heteroleptic cationic phosphorescent iridium(III) complexes.PostprintPeer reviewe

Unprecedented Strong Panchromic Absorption from Proton-Switchable Iridium (III) Azoimidazolate Complexes

Two new heteroleptic iridium(III) complexes bearing an aryldiazoimidazole ligand are reported. These complexes differ structurally with respect to the protonation state of the imidazole ring, but can be independently accessed by varying the synthetic conditions. Their structures have been unequivocally confirmed by X-ray crystal structure analysis, with surprising differences in the structural parameters of the two complexes. The strongly absorbing nature of the free diazoimidazole ligand is enhanced in these iridium complexes, with the protonated cationic complex demonstrating extraordinarily strong panchromic absorption up to 700 nm. The absorption profile of the deprotonated neutral complex is blueshifted by about 100 nm and thus the interconversion between the two complexes as a function of the acidity/basicity of the environment can be readily monitored by absorption spectroscopy. Theoretical calculations revealed the origins of these markedly different absorption properties. Finally, the protonated analogue has been targeted as an acceptor material for organic photovoltaic (OPV) applications, and preliminary results are reported

Palladium(0) NHC complexes : a new avenue to highly efficient phosphorescence

We report the first examples of highly luminescent di-coordinated Pd(0) complexes. Five complexes of the form [Pd(L)(L’)] were synthesized, where L = IPr, SIPr or IPr* NHC ligands and L’ = PCy3, or IPr and SIPr NHC ligands. The photophysical properties of these complexes were determined in toluene solution and in solid state and contrasted to the poorly luminescent reference complex [Pd(IPr)(PPh3)]. Organic light-emitting diodes were successfully fabricated but attained external quantum efficiencies of between 0.3 and 0.7%

Solubilised bright blue-emitting iridium complexes for solution processed OLEDs

Combining a sterically bulky, electron-deficient 2-(2,4-difluorophenyl)-4-(2,4,6- trimethylphenyl)pyridine (dFMesppy) cyclometalating C^N ligand with an electron rich, highly rigidified 1,1’-(α,α’-o-xylylene)-2,2’-biimidazole (o-xylbiim) N^N ligand gives an iridium complex, [Ir(dFMesppy)2(o-Xylbiim)](PF6), that achieves extraordinarily bright blue emission (ΦPL = 90%; λmax = 459 nm in MeCN) for a cationic iridium complex. This complex is compared with two reference complexes bearing 4,4’-di-tert-butyl-2,2’- bipyridine, and solution-processed organic light emitting diodes (OLEDs) have been fabricated from these materials