Phosphorescent Dyes for Organic Light‐Emitting Diodes

Abstract

This article presents general concepts that have guided important developments in our recent research progress regarding room-temperature phosphorescent dyes and their potential applications. We first elaborate the theoretical background for emissive metal complexes and the strategic design of the chelating C-linked 2-pyridylazolate ligands, followed by their feasibility in functionalization and modification in an aim to fine-tune the chemical and photophysical properties. Subsequently, incorporation of 2-pyridylazolate chromophores is illustrated in the synthesis of the highly emissive, charge-neutral Os, Ru, Ir, and Pt complexes. Insights into their photophysical properties are gained from spectroscopy, relaxation dynamics, and theoretical approaches, from which the lowest-lying excited states, competitive radiative decay, and radiationless processes are then analyzed in detail. In view of applications, their potentials for OLEDs have been evaluated. The results, in combination with the fundamental basis, give a conceptual design contributed to the future advances in the field of OLEDs.

Synchrotron ultrafast techniques for photoactive transition metal complexes

“…[68], the structure of which is shown in figure 7b, left-hand panel. The trend expected for structural modifications in photo-excited [Ir 2 (dimen) 4 ] 2+ is the same as discussed above for the Pt-POP complex: light-induced population of a bonding orbital localized between the metal centres induces a pronounced contraction of the metal-metal bond distance [215]. In particular, Hardlup et al extracted a triplet ES Ir-Ir distance of 2.90 Å.…”

“…Owing to differences in the available absorption bands, the Ru 3 (CO) 10 (μ-CO) intermediate is generated by bimolecular recombination of Ru 3 (CO) 10 with a free CO, in ca 50 ns from excitation. 4 ] 2+ , where (dimen) = 1,8-diisocyano-pmenthane [68]. These dimeric systems were selected primarily for their very interesting photochemical properties, but also due to the high scattering power ensured by the metalmetal atom pairs [201][202][203].…”

“…In particular, Hardlup et al extracted a triplet ES Ir-Ir distance of 2.90 Å. In the [Ir 2 (dimen) 4 ] 2+ case, the best agreement with scattering data was obtained by including in the global-fit model two GS structural isomers, differing in separation of metal centres (3.6 Å and 4.3 Å, respectively, see also fit contributions reported in figure 7b, right-hand panel) with equivalent population of 50% each. Such evidence confirmed and complemented recent spectroscopic results [216].…”

The fragment spin difference scheme for triplet-triplet energy transfer coupling

“…[5][6][7][8][9][10] For example, the triplet light emission offers a chance of increasing the quantum yield in the statistics of charge recombination in electroluminescence. [11][12][13][14][15][16] The electronic coupling is one of the factors that determine excitation energy transfer rates. In a singlet-excitation energy transfer, the transition rate between two molecular fragments can be evaluated directly from the optical experiments using Förster's theory 17,18 since Förster's dipoledipole coupling depends on transition dipoles that can be derived from optical spectra.…”

Ir(III)-Based Phosphors with Bipyrazolate Ancillaries; Rational Design, Photophysics, and Applications in Organic Light-Emitting Diodes

“…ppy -, Chart 1). [21][22][23][24] In seeking to further extend the synthetic scope of functional chelating ligands, we were drawn to 5,5'-di(trifluoromethyl)-3,3'-bi-pyrazole (bipzH 2 ) 25 and 5,5'-(1-methylethylidene)-bis(3-trifluoromethyl-1H-pyrazole) (mepzH 2 ) by removal of the two acidic protons to give rise to the associated dianionic chelate ligands (bipz 2-and mepz 2-respectively, Chart 1). In fact, bipz chelate and analogues have been used to afford many Os(II) and Ru(II) metal complexes which exhibit strong near-infrared (NIR) emission 26,27 and planar Pt(II) metal complexes with strong solid-state ππ-stacking interaction, 28 and to serve as efficient sensitizers for dye-sensitized solar cells (DSSC), respectively.…”