Room-temperature phosphorescent materials that emit light in the visible (red, green, and blue; from 400 to 700 nm) have been a major focus of research and development during the past decades, due to their applications in organic light-emitting diodes (OLEDs), light-emitting electrochemical cells, photovoltaic cells, chemical sensors, and bio-imaging. In recent years, near-infrared (NIR) phosphorescence beyond the visible region (700–2500 nm) has emerged as a new, promising, and challenging research field with potential applications toward NIR OLEDs, telecommunications, night vision-readable displays. Moreover, NIR phosphorescence holds promise for in vivo imaging, because cells and tissues exhibit little absorption and auto-fluorescence in this spectral region. This review describes the overall progress made in the past ten years on NIR phosphorescent transition-metal complexes including Cu(I), Cu(II), Cr(III), Re(I), Re(III), Ru(II), Os(II), Ir(III), Pt(II), Pd(II), Au(I), and Au(III) complexes, with a primary focus on material design complemented with a selection of optical, electronic, sensory, and biologic applications. A critical comparison of various NIR phosphorescent materials reported in the literature and a blueprint for future development in this field are also provided.

Near-infrared phosphorescence: materials and applications

1,10-Phenanthroline entails several appealing structural and chemical properties: rigidity, planarity, aromaticity, basicity, chelating capability. This makes it a versatile starting material for synthetic organic, inorganic and supramolecular chemistry. In this tutorial review we examine how the chemical versatility of pristine 1,10-phenanthroline, a weakly fluorescent molecule, has been exploited to design many UV-Vis-NIR luminescent organic derivatives and coordination compounds with transition-metal (Ru(II), Os(II), Rh(III), Cr(III), Pt(II), Zn(II), Cu(I), Ag(I)) and rare-earth (Eu(III),Tb(III), Yb(III), Nd(III), Er(III)) cations. They are utilized for many analytical and technological applications.

1,10-Phenanthrolines: versatile building blocks for luminescent molecules, materials and metal complexes

Publisher Summary This chapter presents a discussion on the coordination chemistry of 2,2’: 6’, 2”-terpyridine and higher oligopyridines. The potentially terdentate ligand 2,2’: 6’, 2”-terpyridine presented, was first isolated by Morgan and Burstall as one of the numerous products from the reaction of pyridine with iron (III) chloride. There has been a considerable increase in the use of these ligands in recent years, prompted in part by the attractive photochemical and photophysical properties exhibited by complexes of the related ligands 2,2’-bipyridine and 1,10-phenanthroline. The chapter discusses stabilization of unusual complexes and states that low oxidation states are characterized by an excess of electron density at the metal atom; stabilization may be achieved by the use of ligands capable of reducing that electron density. One of the simplest ways to reduce the electron density is to design ligands with low-lying vacant orbitals of suitable symmetry for overlap with filled metal orbitals. This results in the transfer of electron density from the metal to the ligand (back-donation). In general, ligand nonbonding or π antibonding orbitals are of the correct symmetry for such overlap. The oligopyridines are ideally suited to such roles; they possess a filled highest occupied molecular orbital (HOMO) and a vacant lowest unoccupied molecular orbital (LUMO) of suitable energies for interaction with metal d orbitals. The chapter also discusses monodentate, bidentate, and bridging; terdentate and higher polydentate; cyclometallated, and others.

The Coordination Chemistry of 2,2′:6′,2″-Terpyridine and Higher Oligopyridines

Metal centered ligand field excited states: Their roles in the design and performance of transition metal based photochemical molecular devices

The composition of the mitochondrial DNA (mtDNA) of the fin whale,Balaenoptera physalus, was determined. The length of the molecule is 16,398 bp, and its organization conforms with that of other mammals. The general similarity between the mtDNA of the fin whale and the cow is greater than the similarity between the fin whale and other species (human, mouse, rat) in which the composition of the entire molecule has been described. The D-loop region of the mtDNA of the fin whale is 81% identical to the D-loop of dolphin DNA, and the central portion of the D-loop is similar to the bovine D-loop. The accumulation of transversions and gaps in the 12S and 16S rRNA genes was assessed by comparing the fin whale, cow, and human. The sequence difference between human and the whale and human and the cow was at the same level, indicating that the rate of evolution of the mtDNA rRNA genes is about the same in artiodactyls and cetaceans. In the 12S rRNA gene an accumulation rate of 0.05% per million years places the separation of cetaceans and artiodactyls at about 55 million years ago. The corresponding figure for human and either the whale or the cow is about 80 million years. In the 16S rRNA gene a 0.08% accumulation rate of transversions and gaps per million years yields concurring figures. A comparison between the cytochromeb gene of the fin whale and cytochromeb sequences in the literature, including dolphin (Stenella) sequences, identified the cetaceans as monophyletic and the artiodactyls as their closest relatives. The comparison between the cytochromeb sequences of the fin whale andStenella showed that differences in codon positions one or two were frequently associated with a change in another codon position.

The complete nucleotide sequence of the mitochondrial DNA of the fin whale, Balaenoptera physalus.

Excited-state behavior of polypyridyl complexes of chromium(III)

Mechanism of the photochemistry and photophysics of the tris(2,2'-bipyridine)chromium(III) ion in aqueous solution

The rate constant of the thermal aquation of chromium complex (Cr(phen)/sub 3//sup 3 +/(phen = 1,10-phenanthroline)) has been determined as a function of pH and temperature; the quantum yield of the photoaquation has been evaluated as a function of excitation wavelength, as a function of pH in the presence of excited-state quenchers iodide, oxygen (I/sup -/, O/sub 2/), and as a function of substrate concentration. The luminescence lifetime and intensity from the /sup 2/T/sub 1///sup 2/E excited states have been measured as a function of pH, (O/sub 2/), (I/sup -/), and (Cr(phen)/sub 3//sup 3 +/). The absorption spectrum of the /sup 2/T/sub 1///sup 2/E excited states has been obtained; the decay of the absorption has been monitored as a function of temperature and solution medium. The thermal, photochemical, and photophysical behavior of Cr(phen)/sub 3//sup 3 +/ in aqueous solution is very similar to that exhibited by Cr(bpy)/sub 3//sup 3 +/ (bpy = 2,2'-bipyridine) and is interpreted in terms of analogous mechanistic steps. It is believed that excitation into spin-allowed states yields /sup 4/T/sub 2/, which undergoes very efficient intersystem crossing to /sup 2/T/sub 1///sup 2/E: these latter states can depopulate via nonradiative decay (including ground-state quenching) or interact with H/submore » 2/O and hydroxyl radicals (OH/sup -/) to yield a Cr(phen)/sub 3/(H/sub 2/O)/sup 3 +/ intermediate, which is the direct precursor of the aquation products. Back intersystem crossing is not regarded as an important process. The thermal aquation of the ground state is visualized as occurring via the same intermediate. The relationship of the results reported here to photoracemization and thermal racemization observatons in the literature is made. 11 figures.« less

Photochemical, photophysical, and thermal behavior of the tris(1,10-phenanthroline)chromium(III) ion in aqueous solution

Determination ofNucleotide Sequences inDNA

Phosphorescence intensity and lifetime and doublet absorption of [Cr(bpy)3]3+(bpy = 2,2′-bipyridine) do not depend on pH (1·0–9·6), whereas the photoaquation quantum yield increases from ⩽ 10–3 at pH 4 to ca. 0·1 at pH 9; complete quenching of the phosphorescence by I– ions causes at least 95% quenching of the photoreaction.

M. S. Henry

Papers

Excited-state behavior of polypyridyl complexes of chromium(III)

Mechanism of the photochemistry and photophysics of the tris(2,2'-bipyridine)chromium(III) ion in aqueous solution

Photochemical, photophysical, and thermal behavior of the tris(1,10-phenanthroline)chromium(III) ion in aqueous solution

Determination ofNucleotide Sequences inDNA

Photochemistry and photophysics of tris(2,2′-bipyridine)chromium(III)