Once the Cinderella amongst the Platinum Group Metals at the Photochemistry Ball, iridium has become of intense interest since the beginning of the decade. Complexes of iridium(III) can be prepared that are highly luminescent, with emission wavelengths tuneable over the whole of the visible region. Whilst most studies have focused on tris-bidentate complexes, a rich and varied chemistry is also possible using tridentate ligands. In this review, we discuss the synthesis and excited-state properties of such complexes, exploring in particular how the number of cyclometallating carbon atoms in the coordination sphere of the metal ion influences the luminescence. Moving from [IrN6]3+ to [IrN3X3] coordination via [IrN5X]2+ and cis/trans-[IrN4X2]+ complexes, where N is a heterocyclic nitrogen and X is an anionic ligand or cyclometallated carbon, a whole range of luminescence efficiencies are encountered, ranging from the barely detectable to room temperature quantum yields approaching unity. We consider the extent to which these profound differences, arising as a result of subtle changes in molecular structure, can be rationalised in terms of the nature of the frontier orbitals.

One of the key issues concerning the development of efficient polymer solar cell technology is the lack of viable materials which absorb in the near‐infrared (NIR) region. This could be resolved by up‐converting energy from the NIR into visible using triplet fusion (TF) with an additional layer that is fabricated separately from the solar cell and deposited on top. Theoretically a maximum upconversion (UC) via TF efficiency of 50% could be obtained. Here, it is demonstrated that in a film of commercially available poly(para‐phenylene vinylene) copolymer “super yellow” (SY) doped with 4% palladium(meso‐tetraphenyl‐tetrabenzoporphyrin) (PdTPBP) sensitizer, an UC efficiency of 6% can be achieved. By using femtosecond and nanosecond spectroscopies it is shown that the main UC efficiency loss mechanism is due to triplet quenching in PdTPBP aggregates. The PdTPBP intersystem crossing rate constant is determined to be 1.8 × 1011 s−1 and the triplet energy transfer rate constant from PdTPBP to SY to be 109 s−1. Quenching in PdTPBP aggregates can account for a triplet concentration loss in the range of 76‐99%. As such, preventing sensitizer aggregation in NIR‐to‐visible upconverting films is crucial and may lead to substantial increase of UC efficiencies in films.

A new family of cationic iridium(III) complexes is reported that contain two cyclometalating terdentate ligands. The complex [Ir(N--C--N-dpyx)(N--N--C-phbpy)]+ (1) contains one N--C--N-coordinating ligand, cyclometalating through the central phenyl ring, and one N--N--C-coordinated ligand, cyclometalated at the peripheral phenyl ring [dpyxH = 1,3-di(2-pyridyl)-4,6-dimethylbenzene; phbpyH = 6-phenyl-2,2'-bipyridine]. This binding mode dictates a mutually cis arrangement of the cyclometalated carbon atoms: the complexes are thus bis-terdentate analogues of the well-known [Ir(N--C-ppy)2(N--N-bpy)]+ family of complexes, which similarly contain a cis-C2N4 coordination environment. The dpyx ligand can be brominated regioselectively at the carbon atom para to the metal under mild conditions. Starting from a modified complex, [Ir(N--C--N-dpyx)(N--N--C-mtbpy-phi-Br)]+ (2), which incorporates a pendent bromophenyl group, a sequential cross-coupling-bromination-cross-coupling strategy can be applied for the stepwise introduction of aryl groups into the ligands, using in situ palladium-catalyzed Suzuki reactions with arylboronic acids [mtbpyH-phi-Br = 4-(p-bromophenyl)-6-(m-tolyl)bipyridine]. Dimetallic complexes 6 and 7 have similarly been prepared by a palladium-catalyzed reaction of complex 2 with 1,4-benzenediboronic acid and 4,4'-biphenyldiboronic acid, respectively. All five monometallic complexes and both dimetallic systems are luminescent in solution, emitting around 630 nm in MeCN at 298 K, with quantum yields in the range of 0.02-0.06, superior to [Ir(ppy)2(bpy)]+. The luminescence, electrochemistry, and singlet-oxygen-sensitizing abilities of the new family of complexes are discussed in the context of the tris-bidentate analogues and related bis-terdentate compounds that contain a trans arrangement of cyclometalated carbon atoms.

A series of luminescent dinuclear platinum(II) complexes incorporating diphenylpyrazine-based bridging ligands (L n ) have been prepared. Both 2,5-diphenylpyrazine (n = 2) and 2,3-diphenylpyrazine (n = 3) are able to undergo cyclometallation of the two phenyl rings, with each metal ion binding to the two nitrogen atoms of the central heterocycle, giving, after treatment with the anion of dipivaloyl methane (dpm), complexes of the formula {Pt(dpm)} 2 L n . These compounds are isomers of the analogous complex of 4,6-diphenylpyrimidine (n = 1). Related complexes of dibenzo(f,h)quinoxaline (n = 4), 2,3-diphenyl-quinoxaline (n = 5) and dibenzo[3,2-a:2',3'-c]phenazine (n = 6) have also been prepared, allowing the effects of strapping together the phenyl rings (n = 4 and 6) and/or extension of the conjugation from pyrazine to quinoxaline (n = 5 and 6) to be investigated. In all cases, the corresponding mononuclear complexes, Pt(dpm)L n H, have been isolated too. All 12 complexes are phosphorescent in solution at ambient temperature. The emission spectra of the dinuclear complexes are consistently red-shifted compared to their mononuclear analogues, as are the lowest-energy absorption bands. Electrochemical data and TD-DFT calculations suggest that this effect arises primarily from a stabilisation of the LUMO. The introduction of the second metal ion also has the effect of substantially increasing extinction coefficients in absorption, and -in most cases -the radiative rate constants. Meanwhile, the extension of conjugation in the heterocycle of L 5 and L 6 , and planarisation of the aromatic system favoured by interannular bond formation in L 4 and L 6 , leads to further red shifts of the absorption and emission spectra to wavelengths that are unusually long for cyclometallated platinum(II) complexes. The results may offer a versatile design strategy for tuning and optimizing the optical properties of d-block metal complexes for contemporary applications. † Northumbria University.

BackgroundAlongside providing a knowledge base and practical skills, undergraduate medical education must prepare graduates to immediately begin practice as qualified doctors. A significant challenge is to provide safe learning opportunities that will optimise students’ preparedness to start work. This study examined UK graduates’ preparedness for clinical practice, and their exposure to real-life and simulated immediate care scenarios during final year placements.MethodA questionnaire measuring students’ perceived preparedness, and their exposure to immediate care scenarios, was distributed to all new Foundation Year 1 doctors (F1s) attending an induction session in one region of the UK.Results356 F1s responded to the questionnaire (91% response rate; 89% of cohort) and data from 344 graduates of UK medical schools were analysed. Respondents were generally prepared for practice, but many reported few ‘hands-on’ experiences of providing immediate care during final year placements (a median of 1–2 experiences).Those who had 1–2 experiences reported no greater preparedness for acute management than those reporting no experience. Several exposures are necessary for a significant increase in perceived preparedness. Real-life experience was a better predictor of preparedness than simulated practice.ConclusionsGaps still remain in medical students’ acute care experience, with a direct relationship to their perceived preparedness. The format and facilitation of placements may need to be addressed in order to enhance the quality of experience during final year.Electronic supplementary materialThe online version of this article (doi:10.1186/1472-6920-14-223) contains supplementary material, which is available to authorized users.