Simple trilayer, deep blue, fluorescent exciplex organic light‐emitting diodes (OLEDs) are reported. These OLEDs emit from an exciplex state formed between the highest occupied molecular orbital (HOMO) of N,N′‐bis(1‐naphthyl)N,N′‐diphenyl‐1,1′‐biphenyl‐4,4′‐diamine (NPB) and lowest unoccupied molecular orbital (LUMO) of 1,3,5‐tri(1‐phenyl‐1H‐benzo[d]imidazol‐2‐yl)phenyl (TPBi) and the NPB singlet manifold, yielding 2.7% external quantum efficiency at 450 nm. It is shown that the majority of the delayed emission in electroluminescence arises from P‐type triplet fusion at NPB sites not E‐type reverse intersystem crossing because of the presence of the NPB triplet state acting as a deep trap.

A new family of anthracene core, highly fluorescent emitters is synthesized which include diphenylamine hole transport end groups. Using a very simple one or two layer organic light emitting diode (OLED) structure, devices without outcoupling achieve an external quantum efficiency of 6% and photonic efficiencies of 20 cd/A. The theoretical maximum efficiency of such devices should not exceed 3.55%. Detailed photophysical characterization shows that for these anthracene based emitters 2T1≤Tn and so in this special case, triplet fusion can achieve a singlet production yield of 0.5. Indeed, delayed electroluminescence measurements show that triplet fusion contributes 59% of all singlets produced in these devices. This demonstrates that when triplet fusion becomes very efficient, fluorescent OLEDs even with very simple structures can approach an internal singlet production yield close to the theoretical absolute maximum of 62.5% and rival phosphorescent‐based OLEDs with the added advantage of much improved stability.

Here, the photophysics and performance of single‐layer light emitting cells (LECs) based on a series of ionic cyclometalated Ir(III) complexes of formulae $\left[ {{\rm Ir}\left( {{\rm ppy}} \right)_{\rm 2} \left( {{\rm bpy}} \right)} \right]^ + {\rm PF}_{\rm 6}^ -$ and $\left[ {{\rm Ir}\left( {{\rm ppy}} \right)_{\rm 2} \left( {{\rm phen}} \right)} \right]^ + {\rm PF}_{\rm 6}^ -$ where ppy, bpy, and phen are 2‐phenylpyridine, substituted bipyridine and substituted phenanthroline ligands, respectively, are reported. Substitution at the NˆN ligand has little effect on the emitting metal‐ligand to ligand charge‐transfer (MLLCT) states and functionalization at this site of the complex leads to only modest changes in emission color. For the more bulky complexes the increase in intermolecular separation leads to reduced exciton migration, which in turn, by suppressing concentration quenching, significantly increases the lifetime of the excited state. On the other hand, the larger intermolecular separation induced by bulky ligands reduces the charge carrier mobility of the materials, which means that higher bias fields are needed to drive the diodes. A brightness of ca. 1000 cd m−2 at 3 V is obtained for complex 5, which demonstrates a beneficial effect of bulky substituents.

We report the synthesis, characterisation, photophysical and electrochemical properties of a series of cationic cyclometallated Ir(III) complexes of general formula [Ir(ppy)(2)(phen)]PF(6) (ppy=2-phenylpyridine, phen=a substituted phenanthroline). A feature of these complexes is that the phen ligands are substituted with one or two 9,9-dihexylfluorenyl substituents to provide extended pi conjugation, for example, the 3-[2-(9,9-dihexylfluorenyl)]phenanthroline and 3,8-bis[2-(9,9-dihexylfluorenyl)]phenanthroline ligands afford complexes 6 and 9, respectively. A single-crystal X-ray diffraction study of a related complex 18 containing the 3,8-bis(4-iodophenyl)phenanthroline ligand, revealed an octahedral coordination of the Ir atom, in which the metallated C atoms of the ppy ligands occupy cis positions. The complexes 6 and 9 displayed reversible oxidation waves in cyclic voltammetric studies (E(ox)(1/2)=+1.18 and +1.20 V, respectively, versus Ag/Ag(+) in CH(2)Cl(2)) assigned to the metal-centred Ir(III)/Ir(IV) couple. The complexes exhibit strong absorption in the UV region in solution spectra, due to spin-allowed ligand-centred (LC) (1)pi-pi* transitions; moderately intense bands occur at approximately 360-390 nm which are red-shifted with increased ligand length. The photoluminescence spectra of all the complexes were characterised by a broad band at lambda(max) approximately 595 nm assigned to a combination of (3)MLCT and (3)pi-->pi* states. The long emission lifetimes (in the microsecond time-scale) are indicative of phosphorescence: the increased ligand conjugation length in complexes 9 and 17 leads to increased lifetimes for the complexes (tau=2.56 and 2.57 micros in MeCN, respectively) compared to monofluorenyl analogues 6 and 15 (tau=1.43 and 1.39 micros, respectively). DFT calculations of the geometries and electronic structures of complexes 6', 9' (for both singlet ground state (S(0)) and triplet first excited (T(1)) states) and 18 have been performed. In the singlet ground state (S(0)) HOMO orbitals in the complexes are spread between the Ir atom and benzene rings of the phenylpyridine ligand, whereas the LUMO is mainly located on the phenanthroline ligand. Analysis of orbital localisations for the first excited (T(1)) state have been performed and compared with spectroscopic data. Spin-coated light-emitting cells (LECs) have been fabricated with the device structures ITO/PEDOT:PSS/Ir complex/Al, or Ba capped with Al (ITO=indium tin oxide, PEDOT=poly(3,4-ethylenedioxythiophene), PSS=poly(styrene) sulfonate). A maximum brightness efficiency of 9 cd A(-1) has been attained at a bias of 9 V for 17 with a Ba/Al cathode. The devices operated in air with no reduction in efficiency after storage for one week in air.

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Organic light emitting diodes (OLEDs) are an attractive proposition for replacing large area Lambertian sources in lighting systems. In this paper we investigate both illumination and communication properties of OLED based lighting configurations in a typical room. Two lighting designs are introduced and compared by deterministic and Monte-Carlo simulations. These show that there is considerable potential to optimize both the illumination levels (and hence the received signal to noise ratio for communications) and that sufficient bandwidth is available (when considering that of the OLED) for communications.

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