Ru(II) polypyridine complexes: photophysics, photochemistry, eletrochemistry, and chemiluminescence

http://europepmc.org/articles/PMC4146684?pdf=render

Cisplatin in cancer therapy: molecular mechanisms of action

Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

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Lanthanide luminescence for functional materials and bio-sciences

Lanthanide-based luminescent hybrid materials.

Strong Closed-Shell Interactions in Inorganic Chemistry.

The triplet state of organo-transition metal compounds. Triplet harvesting and singlet harvesting for efficient OLEDs

1 Triplet Emitters for Organic Light-Emitting Diodes: Basic Properties (Hartmut Yersin and Walter J. Finkenzeller) 2 Spin Correlations in Organic Light-Emitting Diodes (Manfred J. Walter and John M. Lupton) 3 Cyclometallated Organoiridium Complexes as Emitters in Electrophosphorescent Devices (Peter I. Djurovich and Mark E. Thompson) 4 Highly Effi cient Red-Phosphorescent Iridium Complexes (Akira Tsuboyama, Shinjiro Okada, and Kazunori Ueno) 5 Pyridyl Azolate Based Luminescent Complexes: Strategic Design, Photophysics, and Applications (Yun Chi and Pi-Tai Chou) 6 Physical Processes in Polymer-Based Electrophosphorescent Devices (Xiao-Hui Yang, Frank Jaiser, and Dieter Neher) 7 Phosphorescent Platinum(II) Materials for OLED Applications (Hai-Feng Xiang, Siu-Wai Lai, P. T. Lai, and Chi-Ming Che) 8 Energy-Transfer Processes between Phosphorescent Guest and Fluorescent Host Molecules in Phosphorescent OLEDs (Isao Tanaka and Shizuo Tokito) 9 High-Effi ciency Phosphorescent Polymer LEDs (Addy van Dijken, Klemens Brunner, Herbert Borner, and Bea M.W. Langeveld) 10 Electroluminescence from Metal-Containing Polymers and Metal Complexes with Functional Ligands (Chris Shuk Kwan Mak, and Wai Kin Chan) 11 Molecular Engineering of Iridium Complexes and their Application in Organic Light Emitting Devices (Mohammad K. Nazeeruddin, Cedric Klein, Michael Gratzel, Libero Zuppiroli, and Detlef Berner) 12 Progress in Electroluminescence Based on Lanthanide Complexes (Zu-Qiang Bian and Chun-Hui Huang)

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Highly efficient OLEDs with phosphorescent materials

Strongly luminescent neutral copper(I) complexes of the type Cu(pop)(NN), with pop = bis(2-(diphenylphosphanyl)phenyl)ether and NN = bis(pyrazol-1-yl)borohydrate (pz(2)BH(2)), tetrakis(pyrazol-1-yl)borate (pz(4)B), or bis(pyrazol-1-yl)-biphenyl-borate (pz(2)Bph(2)), are readily accessible in reactions of Cu(acetonitrile)(4)(+) with equimolar amounts of the pop and NN ligands at ambient temperature. All products were characterized by means of single crystal X-ray diffractometry. The compounds exhibit very strong blue/white luminescence with emission quantum yields of up to 90%. Investigations of spectroscopic properties and the emission decay behavior in the temperature range between 1.6 K and ambient temperature allow us to assign the emitting electronic states. Below 100 K, the emission decay times are in the order of many hundreds of microseconds. Therefore, it is concluded that the emission stems from the lowest triplet state. This state is assigned to a metal-to-ligand charge-transfer state (3MLCT) involving Cu-3dand pop-π* orbitals. With temperature increase, the emission decay time is drastically reduced, e.g. to 13 μs [corrected] (Cu(pop)-(pz(2)Bph(2))), at ambient temperature. At this temperature, the complexes exhibit high emission quantum yields, as neat material or doped into poly(methyl methacrylate) (PMMA). This behavior is assigned to an efficient thermal population of a singlet state (being classified as (1)MLCT), which lies only 800 to 1300 cm(-1) above the triplet state, depending on the individual complex. Thus, the resulting emission at ambient temperature largely represents a fluorescence. For applications in OLEDs and LEECs, for example, this type of thermally activated delayed fluorescence (TADF) creates a new mechanism that allows to harvest both singlet and triplet excitons (excitations) in the lowest singlet state. This effect of singlet harvesting leads to drastically higher radiative rates than obtainable for emissions from triplet states of Cu(I) complexes.

Blue-Light Emission of Cu(I) Complexes and Singlet Harvesting

Triplet emitter materials present attractive possibilities for optimizations of organic/organometallic light emitting diodes (OLEDs) This is due to the significantly higher efficiencies obtainable with these compounds ascompared to organic emitters In this contribution, first a schematic introduction is given, how an OLED device is built-up and why multi-layer structures are preferred Then a basic model is presented, how electron-hole recombination, ie the exciton formation process, can be visualized and how the singlet and triplet states of the (doped) emitter compounds are populated This takes place by specific singlet and triplet paths The occurrence of such paths is explained by taking into account that the dynamical process of exciton trapping involves dopant-to-matrix charge transfer states ( 1  3 DMCT states) It is also explained, why the excitation energy is harvested in the lowest triplet state of organo-transition-metal complexes Due to spin statistics, one can in principle obtain an efficiency of a factor of four higher than using organic singlet emitter molecules Simple comparisons suggest that electron-hole recombination should preferentially occur on the triplet emitter itself, rather than on matrix molecules with subsequent energy transfer to the emitter Further, it is pointed out that essential photophysical properties of organometallic triplet emitters depend systematically on the metal participation in the triplet state and on the effective spin-orbit coupling These factors control the amount of zero-field splitting (ZFS) of the triplet state into substates Increase of ZFS corresponds to higher metal character in the triplet state Higher metal character reduces the energy difference between excited singlet and triplet states, enhances the singlet-triplet intersystem crossing rate, lowers the emission decay time, changes the vibrational satellite structure, decreases the excited state reorganization energy, etc These effects are discussed by referring to well characterized compounds Based on a new ordering scheme presented for triplet emitter materials, a controlled development of compounds with pre-defined photophysical properties becomes possible

Hartmut Yersin

Papers

The triplet state of organo-transition metal compounds. Triplet harvesting and singlet harvesting for efficient OLEDs

Highly efficient OLEDs with phosphorescent materials

Blue-Light Emission of Cu(I) Complexes and Singlet Harvesting

Triplet emitters for OLED applications. Mechanisms of exciton trapping and control of emission properties

Cu(I) complexes – Thermally activated delayed fluorescence. Photophysical approach and material design