Organometallic Complexes as Hole-Transporting Materials in Organic Light-Emitting Diodes

Picosecond Metal-to-Ligand Charge-Transfer Deactivation in Co(ppy)3 via Jahn-Teller Distortion

The excited-state dynamics of fac-Co(ppy)3, where ppy = 2-[2-(pyridyl)phenyl], are measured with femtosecond UV-vis transient absorption spectroscopy. The initial state is confirmed with spectroelectrochemistry to have significant metal-to-ligand charge transfer (MLCT) character, unlike other Co complexes that generally have ligand-to-metal charge transfer or ligand-field transitions in this energy range. Ground-state recovery occurs in 8.65 ps in dichloromethane. Density functional theory calculations show that the MLCT state undergoes Jahn-Teller distortion and converts to a five-coordinate triplet metal-centered state in which one Co-N bond is broken. The results highlight a potential pitfall of heteroleptic bidentate ligands when designing strong-field ligands for transition-metal chromophores.

An Earth-abundant cobalt based photocatalyst: visible light induced direct (het)arene C-H arylation and CO2 capture

In this work, we have reported a noble metal free heterogeneous photocatalyst to carry out direct (het)arene C-H arylation and solvent-free CO₂ capture via single-electron transfer processes at room temperature and under pressure. The catalytic system comprises a cobalt(III) complex grafted over the silica coated magnetic support for the efficient recovery of the photocatalytic moiety without hampering its light-harvesting capability. The novel Earth-abundant cobalt(III) based photocatalyst possesses various fascinating properties such as high surface area to volume ratios, large pore volume, crystalline behaviour, high metal loading, excellent stability and reusability. The general efficacy of the highly abundant and low-cost cobalt based heterogeneous nanocatalyst was checked for the selective conversion of aryldiazonium salts into synthetically and pharmaceutically significant biaryl motifs under ambient conditions upon irradiation with visible light. The highly efficient photocatalytic conversion of carbon dioxide (CO₂) to a value-added chemical was accomplished under mild reaction conditions with high selectivity, showing the added benefit of operational simplicity.

Synthesis and Computational Study of a Pyridylcarbene Fe(II) Complex: Unexpected Effects of fac/ mer Isomerism in Metal-to-Ligand Triplet Potential Energy Surfaces

The synthesis and the steady-state absorption spectrum of a new pyridine-imidazolylidene Fe(II) complex (Fe-NHC) are presented. A detailed mechanism of the triplet metal-to-ligand charge-transfer states decay is provided on the basis of minimum energy path (MEP) calculations used to connect the lowest-lying singlet, triplet, and quintet state minima. The competition between the different decay pathways involved in the photoresponse is assessed by analyzing the shapes of the obtained potential energy surfaces. A qualitative difference between facial ( fac) and meridional ( mer) isomers' potential energy surface (PES) topologies is evidenced for the first time in iron-based complexes. Indeed, the mer complex shows a steeper triplet path toward the corresponding ³MC minimum, which lies at a lower energy as compared to the fac isomer, thus pointing to a faster triplet decay of the former. Furthermore, while a major role of the metal-centered quintet state population from the triplet ³MC region is excluded, we identify the enlargement of iron-nitrogen bonds as the main normal modes driving the excited-state decay.

Design and synthesis of a luminescent cyclometalated iridium(III) complex having N,N-diethylamino group that stains acidic intracellular organelles and induces cell death by photoirradiation

Cyclometalated iridium(III) complexes have received considerable attention and are important candidates for use as luminescent probes for cellular imaging because of their potential photophysical properties. We previously reported that fac-Ir(atpy)(3)4 (atpy = 2-(5'-amino-4'-tolyl)pyridine) containing three amino groups at the 5'-position of the atpy ligand shows a maximum red emission (at around 600 nm) under neutral and basic conditions and a green emission (at 531 nm) at acidic pH (pH 3-4). In this Article, we report on the design and synthesis of a new pH-sensitive cyclometalated Ir(III) complex containing a 2-(5'-N,N-diethylamino-4'-tolyl)pyridine (deatpy) ligand, fac-Ir(deatpy)(3)5. The complex exhibits a considerable change in emission intensity between neutral and slightly acidic pH (pH 6.5-7.4). Luminescence microscopic studies using HeLa-S3 cells indicate that 5 can be used to selectively stain lysosome, an acidic organelle in cells. Moreover, complex 5 is capable of generating singlet oxygen in a pH-dependent manner and inducing the death of HeLa-S3 cells upon photoirradiation at 377 or 470 nm.

Borazine materials for organic optoelectronic applications

Borazine materials have been demonstrated to be a new class of multifunctional and thermally stable materials with high electron (10(-3) cm2 V(-1) s(-1)) and moderate hole (10(-4) cm2 V(-1) s(-1)) mobilities for applications in electroluminescent devices.