Muna R. A. Al-Mandhary

Bio: Muna R. A. Al-Mandhary is an academic researcher from Sultan Qaboos University. The author has contributed to research in topics: Platinum & Ligand. The author has an hindex of 16, co-authored 26 publications receiving 1528 citations. Previous affiliations of Muna R. A. Al-Mandhary include University of Cambridge.

The energy gap law for triplet states in Pt-containing conjugated polymers and monomers.

Abstract: The energy gap law established for aromatic hydrocarbons and rare earth ions relates the nonradiative decay rate to the energy gap of a transition through a multiphonon emission process. We show that this energy gap law can be applied to the phosphoresce of a series of conjugated polymers and monomers for which the radiative decay rate has been enhanced through incorporation of a heavy metal. We find that the nonradiative decay rate from the triplet state T(1) increases exponentially with decreasing T(1)-S(0) gap for the polymers and monomers at 300 and 20 K. Comparison of the nonradiative decay of polymers with that of their corresponding monomers highlights the role of electron-lattice coupling.

Evolution of lowest singlet and triplet excited states with number of thienyl rings in platinum poly-ynes

Abstract: Soluble, rigid-rod organometallic polymers trans-[-Pt(PBu3n)2–C≡C–R–C≡C–]∞ (R=bithienyl 2, terthienyl 3) have been synthesized in good yields by the CuI-catalyzed dehydrohalogenation reaction of trans-[Pt(PBu3n)2Cl2] with one equivalent of the diterminal alkynyl oligothiophenes H–C≡C–R–C≡C–H in CH2Cl2/iPr2NH at room temperature. We report the thermal properties, and the optical absorption, photoluminescence, and photocurrent action spectra of 1 (trans-[–Pt(PBu3n)2–C≡C–R–C≡C–]∞, R=thienyl), 2 and 3 as a function of the number of thiophene rings within the bridging ligand. With increasing thiophene content, the optical gap is reduced and the vibronic structure of the singlet emission changes toward that typical for oligothiophenes. We also find the intersystem crossing from the singlet excited state to the triplet excited state to become reduced, while the singlet–triplet energy gap remains unaltered. The latter implies that, in these systems, the T1 triplet excited state is extended over several thiophene ...

Synthesis, Electrochemistry, and Spectroscopy of Blue Platinum(II) Polyynes and Diynes.

Abstract: The smallest band gap observed so far (1.77 eV) for an organometallic polymer is exhibited by the blue, rigid-rod polymer 2, which is prepared by the reaction of trans-[PtCl2(PnBu3)2] with one equivalent of 1.

Triplet states in a series of Pt-containing ethynylenes

Abstract: By use of optical steady state and time resolved spectroscopy, we studied the evolution of the triplet excited state in a series of six ethynylenic polymers of the structure [-Pt(PBu3n)2-C≡C-R-C≡C-]n where the spacer unit R is systematically varied to give optical gaps from 1.7–3.0 eV. The inclusion of platinum in the polymer backbone induces a strong spin-orbit coupling such that triplet state emission (phosphorescence) associated with the conjugated system can be detected. Throughout the series we find the S1-T1 (singlet-triplet) energy splitting to be independent of the spacer R, such that the T1 state is always 0.7±0.1 eV below the S1 state. With decreasing optical gap, the intensity and lifetime of the triplet state emission were seen to reduce in accordance with the energy gap law.

Synthesis, characterisation and optical spectroscopy of diynes and poly-ynes containing derivatised fluorenes in the backbone

Abstract: A series of trimethylsilyl-protected and terminal mono- and bis-alkynes based on 9,9-dioctylfluorene, 2-(trimethylsilylethynyl)-9,9-dioctylfluorene 1a, 2-ethynyl-9,9-dioctylfluorene 1b, 2,7-bis(trimethylsilylethynyl)-9,9-dioctylfluorene 2a, 2,7-bis(ethynyl)-9,9-dioctylfluorene 2b, have been synthesised. Reaction of trans-[(PnBu3)2PtCl2] with 2 equivalents of the terminal ethyne 1b yields the mononuclear platinum(II) diyne 3, reaction of trans-[(Ph)(Et3P)2PtCl] with 0.5 equivalents of the diterminal ethyne 2b gives the dinuclear platinum(II) diyne 4 while 1 ∶ 1 reaction between trans-[(PnBu3)2PtCl2] and 2b gives the platinum(II) poly-yne 5. Treatment of 2,5-dioctyloxy-1,4-diiodobenzene with 1b in 1 ∶ 2 stoichiometry produces the organic di-yne 6 while 1 ∶ 1 reaction between 2,5-dioctyloxy-1,4-diiodobenzene and 2b, 2,7-bis(ethynyl)fluorene or 2,7-bis(ethynyl)fluoren-9-one produces the organic co-poly-ynes 7–9. All the new materials have been characterised by analytical and spectroscopic methods and the single crystal X-ray structures of 2a and 3 have been determined. The diynes and poly-ynes are soluble in organic solvents and are readily cast into thin films. Optical spectroscopic measurements reveal that the attachment of octyl side-chains on the fluorenyl spacer reduces inter-chain interaction in the poly-ynes while a fluorenonyl spacer creates a donor–acceptor interaction along the rigid backbone of the organometallic poly-ynes and organic co-poly-ynes.

Synthesis of a carbon nitride structure for visible-light catalysis by copolymerization

Abstract: and nonmetallic elements (N, C, B) creates localized/ delocalized states in the band gap and thus extends its optical absorption to the visible region, but doping usually comes with accelerated charge recombination and lower stability of the doped materials. Meanwhile, various other inorganic, non-TiO2-based, visible-light catalysts have been developed (e.g., metal oxides, nitrides, sulfides, phosphides, and their mixed solid solutions), whereby Ga, Ge, In, Ta, Nb, and W are the main metal constituents. However, sustained utilization of solar energy calls for the development of more abundant and stable catalysts working with visible light, and this has remained challenging so far. Recently, a polymeric semiconductor on the basis of a defecteous graphitic carbon nitride (g-C3N4), was introduced as a metal-free photocatalyst which fulfills the basic requirements for a water-splitting catalyst, including being abundant, stable, and responsive to visible light. In the following, we use the notation “g-C3N4” to describe this class of materials rather than the idealized structure. The most active system is in fact presumably an N-bridged “poly(tri-s-triazine)”, already described by Liebig as “melon”. A semiconductor structure with band edges straddling the water redox potential was revealed for melon by DFT calculations, albeit electrochemical analysis is still awaited. g-C3N4 is considered to be the most stable phase of covalent carbon nitride, and facile synthesis of the melon substructure from simple liquid precursors and monomers allows easy engineering of carbon nitride materials to achieve the desired nanostructures via soft-chemical processing routes and methods. For instance, a high surface area (67–400 mg ) can be imparted on g-C3N4 materials by polymerization of cyanamide on a silica template, which results in photocatalytically more active g-C3N4 nanostructures. [8] Metal-doped gC3N4 can also be conveniently obtained by polymerization of dicyandiamine in the presence of metal salts, and thus multifunctionalization of such materials for a variety of applications can be achieved. Most importantly, the electronic and optical properties of carbon nitride, regarded as a polymer semiconductor, are in principle adjustable by organic protocols. Such organic protocols have been widely used to control the performance of traditional p-conjugated polymers, for example, to improve solar-cell efficiencies by constructing copolymerized donor–acceptor structures, or to modify electronic properties by co-blending with p/n-type organic dopants. Our aim was to use such organic modifications to extend the insufficient light absorption of g-C3N4 (a result of its large band gap of 2.7 eV, which corresponds to wavelengths shorter than 460 nm) towards the maximum of the solar spectrum. Here we demonstrate that the optical absorption of carbon nitride semiconductor materials is extendable into the visible region up to about 750 nm by simple copolymerization with organic monomers like barbituric acid (BA). The electronic and photoelectric properties of the modified carbon nitrides were then investigated to elucidate their enhanced activity for hydrogen production from water containing an appropriate sacrificial reagent with visible light. In principle, BA can be directly incorporated into the classical carbon nitride condensation scheme (Scheme 1). New carbon nitride structures were therefore synthesized by dissolving dicyandiamide with different amounts of BA in water, followed by thermally induced copolymerization at 823 K. For simplicity, the resulting samples are denoted CNBx, where x (0.05, 0.1, 0.2, 0.5, 1, 2) refers to the weighedin amount of BA. The structure, texture, and electrochemical properties of these materials were characterized, and their photochemical performance analyzed. Their XRD patterns (Figure S1, Supporting Information) are dominated by the characteristic (002) peak at 27.48 of a graphitic, layered structure with an interlayer distance of d = [*] J. Zhang, X. Chen , Prof. X. Fu, Prof. X. Wang State Key Laboratory Breeding Base of Photocatalysis Fuzhou University, Fuzhou 350002 (China) E-mail: xcwang@fzu.edu.cn

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

Abstract: Based on a very comprehensive set of experimental data and on theoretical models, an understanding of the triplet state properties of organo-transition metal compounds is worked out Important trends and guidelines for controlling photophysical properties are revealed In this respect, we focus on spin–orbit coupling (SOC) and its importance for radiative as well as for nonradiative transitions between the lowest triplet state and the electronic ground state Moreover, as is discussed on the basis of an extensive data set, summarized for the first time, the efficiency of SOC also depends on the geometry of a complex The investigations are exemplified and supported by instructive case studies, such as efficient blue and very efficient green and red emitters Additionally, trends being important for applications of these compounds as emitters in OLEDs are worked out In particular, the properties of the emitters are discussed with respect to the harvesting of singlet and triplet excitons that are generated in the course of the electroluminescence process The well-known triplet harvesting effect is compared to the recently discovered singlet harvesting effect This latter mechanism is illustrated by use of a blue light emitting Cu(I) complex, which represents an efficient fluorescent emitter at ambient temperature By this mechanism, 100% of the generated singlet and triplet excitons can, at least in principle, be harvested by the emitting singlet state Potentially, this new mechanism can successfully be applied in future OLED lighting with a distinctly reduced roll-off of the efficiency

Photochemistry and Photophysics of Coordination Compounds: Platinum

Abstract: This chapter provides an overview of the luminescence properties of platinum(II) complexes, exploring how the excited states involved in emission are influenced by the ligands around the metal ion. The square planar nature of d8 Pt(II) complexes has many implications, leading to properties and applications that are not open to d6 complexes. For example, axial intermolecular interactions can lead to new excited states not present in the isolated molecules. This review focuses on complexes containing one or more chelating ligands, of which at least one contains a heterocyclic ring such as pyridine. Thus, we explore the properties of a range of bipyridyl (bpy) and terpyridyl (tpy) complexes, and how they are influenced by the identity of the other ligands that complete the coordination sphere of the Pt(II) ion, such as halide, cyanide, thiolates and acetylides. We consider the sometimes dramatic influence of substituents in the bpy/tpy ligands in producing other excited states that may be much more intensely emissive than those of the parent complexes. The influence of cyclometallation on excited states is discussed, and how it can lead to highly emissive complexes: a range of cyclometallated systems are reviewed, with bidentate and terdentate ligands incorporating one or more metal–carbon bonds. Contemporary applications in areas such as sensors, photoinduced electron transfer, and organic light-emitting devices are highlighted.