Enrique Ortí

Near-Quantitative Internal Quantum Efficiency in a Light-Emitting Electrochemical Cell

A green-light-emitting iridium(III) complex was prepared that has a photoluminescence quantum yield in a thin-film configuration of almost unity. When used in a simple solid-state single-layer light-emitting electrochemical cell, it yielded an external quantum efficiency of nearly 15% and a power efficiency of 38 Lm/W. We argue that these high external efficiencies are only possible if near-quantitative internal electron-to-photon conversion occurs. This shows that the limiting factor for the efficiency of these devices is the photoluminescence quantum yield in a solid film configuration. The observed efficiencies show the prospect of these simple electroluminescent devices for lighting and signage applications.

A supramolecularly-caged ionic iridium (III) complex yielding bright and very stable solid-state light-emitting electrochemical cells

A new iridium(III) complex showing intramolecular interligand pi-stacking has been synthesized and used to improve the stability of single-component, solid-state light-emitting electrochemical cell (LEC) devices. The pi-stacking results in the formation of a very stable supramolecularly caged complex. LECs using this complex show extraordinary stabilities (estimated lifetime of 600 h) and luminance values (average luminance of 230 cd m-2) indicating the path toward stable ionic complexes for use in LECs reaching stabilities required for practical applications.

Origin of the large spectral shift in electroluminescence in a blue light emitting cationic iridium(III) complex

A new, but archetypal compound [Ir(ppy-F2)2Me4phen]PF6, where ppy-F2 is 2-(2′,4′-fluorophenyl)pyridine and Me4phen is 3,4,7,8-tetramethyl-1,10-phenanthroline, was synthesized and used to prepare a solid-state light-emitting electrochemical cell (LEEC). This complex emits blue light with a maximum at 476 nm when photoexcited in a thin film, with a photoluminescence quantum yield of 52%. It yields an efficient single-component solid-state electroluminescence device with a current efficiency reaching 5.5 cd A−1 and a maximum power efficiency of 5.8 Lm Watt−1. However, the electroluminescence spectrum is shifted with respect to the photoluminescence spectrum by 80 nm resulting in the emission of green light. We demonstrate that this unexpected shift in emission spectrum does not originate from the mode of excitation, nor from the presence of large concentrations of ions, but is related to the concentration of the ionic transition metal complex in the thin film. The origin of the concentration-dependent emission is extensively commented on and argued to be related to the population of either 3LC π–π* or 3MLCT triplet states, in diluted and concentrated films, respectively. Using quantum chemical calculations we demonstrate that three low-energy triplet states are present with only 0.1 eV difference in energy and that their associated emission wavelengths differ by as much as 60 nm from each other.

Simple, Fast, Bright, and Stable Light Sources

In this work we show that solution-processed light-emitting electrochemical cells (LECs) based on only an ionic iridium complex and a small amount of ionic liquid exhibit exceptionally good performances when applying a pulsed current: sub-second turn-on times and almost constant high luminances (>600 cd m(-2) ) and power efficiencies over the first 600 h. This demonstrates the potential of LECs for applications in solid-state signage and lighting.

Copper(I) complexes for sustainable light-emitting electrochemical cells

Four prototype heteroleptic copper(I) complexes [Cu(bpy)(pop)][PF6] (bpy = 2,2′-bipyridine, pop = bis(2-(diphenylphosphino)phenyl)ether), [Cu(phen)(pop)][PF6] (phen = 1,10-phenanthroline), [Cu(bpy)(pdpb)][PF6] (pdpb = 1,2-bis(diphenylphosphino)benzene) and [Cu(phen)(pdpb)][PF6] are presented. The synthesis, X-ray structures, solution and solid-state photophysical studies, and the performance in light-emitting electrochemical cells (LECs) of these complexes are described. Their photophysical properties are interpreted with the help of density functional theory (DFT) calculations. The photophysical studies in solution and in the solid-state indicate that these copper(I) complexes show good luminescent properties which allow them to be used as active materials in electroluminescent devices such as LECs. Additionally, these materials are very attractive since we can take advantage of their low-cost, due to the copper abundance, and their limited environmental damaging effects for producing cheap large-area panels based on the LEC technology for lighting applications. LEC devices were fabricated using the four prototype copper(I) complexes together with an ionic liquid (IL), 1-ethyl-3-methylimidazolium hexafluoridophosphate, at a molar ratio of 1 : 1. They yield devices that are comparable to those obtained for most LEC devices based on ruthenium(II) and iridium(III) complexes. Hence, this work shows that promising electroluminescent devices can be prepared using cheap and environmentally friendly copper(I) complexes.

Discrete Supramolecular Donor–Acceptor Complexes†

The renewed interest in noncovalently associating electroactive molecules arises in part from the quest for new organic materials that convert solar energy into electrical/ chemical equivalents. In this context, the formation of charge-separated states is a key prerequisite. Charge-transfer events triggered by light have been studied in supramolecular donor–acceptor systems based on hydrogen bonds and coordinative metal bonds. Although many of the most widely utilized electroactive fragments feature large pconjugated surfaces, to date the use of p–p aromatic interactions has mainly been limited to the construction of semi-infinite ensembles of chromophores either to achieve charge transport—with the known example of charge transfer through DNA bases—or to increase the efficiency of light absorption. Detailed studies on charge-transfer interactions in discrete supramolecular systems held together by p–p aromatic interactions are surprisingly scarce. Recently, we succeeded in the realization of donor–acceptor supramolecules based on the recognition of the convex exterior of C60 by the concave surface of p-extended tetrathiafulvalene derivatives. Numerous incentives, especially in the context of constructing more efficient optoelectronic devices, are offered by these C60/exTTF materials. Herein we describe the physicochemical characterization of the supramolecular donor–acceptor p complexes and provide a theoretical description of the underlying host–guest interactions. The meta and para tweezers (MTW and PTW, respectively) share a straightforward design, in which two 2-[9-(1,3dithiol-2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole (exTTF) units are connected through isophthalic or terephthalic diester spacers, respectively (Scheme 1). MTW and

A theoretical study of the electronic spectrum of naphthalene

Abstract Ab initio calculations have been carried out for the singlet and triplet excited states of naphthalene. Excitation energies have been calculated using multiconfigurational second order perturbation theory (CASPT2). The study comprises a total of 32 states, ten singlet and ten triplet excited states, in addition to the 1au→3s, 3p, dipole-allowed 3d, and 2b1u→3s, 3p Rydberg states. Computed excitation energies and oscillator strengths make possible confident assignments of the main features reported in the singlet-singlet and triplet-triplet experimental spectra.

A deep-blue emitting charged bis-cyclometallated iridium(III) complex for light-emitting electrochemical cells

We report here a new cationic bis-cyclometallated iridium(III) complex, 1, with deep-blue emission at 440 nm and its use in Light-emitting Electrochemical Cells (LECs). The design is based on the 2′,6′-difluoro-2,3′-bipyridine skeleton as the cyclometallating ligand and a bis-imidazolium carbene-type ancillary ligand. Furthermore, bulky tert-butyl substituents are used to limit the intermolecular interactions. LECs have been driven both at constant voltage (6 V) and constant current (2.5 mA cm−2). The performances are significantly improved with the latter method, resulting overall in one of the best reported greenish-blue LECs having fast response (17 s), light intensity over 100 cd m−2 and a reasonable efficiency of almost 5 cd A−1.

A bis-exTTF macrocyclic receptor that associates C60 with micromolar affinity.

An exTTF-based macrocyclic receptor that associates C(60) with a binding constant >10(6) M(-1) in chlorobenzene at room temperature is described. This represents an improvement of 3 orders of magnitude with respect to the previous examples of exTTF-based receptors and one of the highest binding constants toward C(60) reported to date.

Theoretical determination of the electronic spectrum of free base porphin

Abstract The main features of the electronic spectrum of free base porphin are determined by means of multiconfigurational second-order perturbation (CASPT2) theory. The calculations comprise the optically allowed singlet states associated to the Q and B bands and the corresponding triplet states. The computed excitation energies deviate from the available experimental data by less than 0.3 eV in all the cases where a comparison is possible. It is found that both σ- and π-electron correlation contributions have to be taken into account in order to give a balanced description of the excited states. A limited theoretical treatment, based on only β-electron correlation or only partially including the correlation of the σ electrons, is not sufficient.