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Research has been conducted on the hetero- and homometallic aquare complexes. The preparation and photochemistry of the self-assembly transition-metal-based macrocyclic compounds bridged by the photoisomerizable 4,4'-azopyridine or 1,2-bis(4-pyridyl)ethylene ligand are described.

Research has been conducted on the polypyridyl d (super)6-W(0) and Re(I) carbonyl complexes. The results of the photophysical and photochemical analysis of some of these complexes which incorporate ferrocene end-capped pyridine ligands are reported.

Research demonstrates synthesis of four octanuclear organometallic squares by self-assembly between ligand complexes. Structural and elemental analyses reveal that the squares incorporate terpyridyl metal complexes as bridging ligands. All four heterometallic complexes exhibit strong visible absorption characteristic of iron, rubidium, or osmium metals.

A photochemical study of the (eta-5-C5H5)Fe(Co)2 was presented to determine the optimum photochemical conditions for the complexes. The heterocyclic cleavage of iodide which was needed to form (eta-5-C5H5)Fe(Co)2(eta-1-N-pyrrolyl) was investigated due to irradiation at various wavelengths. Results revealed that most effective photoconversion took place with excitation at long wavelengths into weak low-lying absorption bands and long-wavelength irradiation was a means of effecting heterolytic Fe-I dissociation which facilitates synthetic pathway to azaferrocene.

Photoreactivity measurements were conducted on the intermolecular C-H bond activation process of (HBPz'3)Rh(CO)2 in different hydrocarbon solutions at room temperature. Absolute quantum efficiencies for C-H activation were obtained and were observed to be dependent on the excitation wavelength and the nature of the substrate. A short-lived monocarbonyl (HBPz'3)Rh(CO) intermediate was implicated in the C-H bond activation pathway, and this reaction was facilitated most effectively upon ultraviolet photolysis.

The thermal chemistry and photochemistry of the intermolecular C-H bond activating complex (HBPz'3)Rh(CO)2, where Pz = 3,5-dimethylpyrazolyl, have been investigated. Excitations were performed at 313-458 nm into the lowest energy absorption band and were monitored by in-situ UV-vis and FTIR spectroscopies. The results showed that the photochemistry is exceptionally clean, with complete conversion of the complex to the (HBPz'3)Rh(CO)(R)H photoproducts. The photochemical reactions were shown to originate from two low-lying LF state with different activities.

A kinetic procedure for measuring the photochemical quantum efficiencies of reactions in which several components have overlapping absorbances is fully described. This method has been found to be particularly suitable for photochemical determinations where inner filter effects are substantial, such as those typically observed in the ligand substitution and intermolecular C-H/Si-H bond activation mechanisms of metal complexes. The quantitative measurement of the Si-H bond activation photochemistry of ([[Eta].sup.5]-[C.sub.5][H.sub.5])Rh[(CO).sub.2] in triethylsilane solution is demonstrated in detail, although the procedure has widespread application in photochemistry.

A method for monitoring the extent of photoinitiated acrylate and epoxy polymerixations is presented. The complex fac-CIRe(CO)3(4,7-Ph2phen) (4,7-Ph2phen = 4,7-diphenyl-1,10-phananthroline) is an effective spectroscopic probe which can monitor the progress of photochemical curing reactions. Its useful key properties include solubility and thermal stability in nonpolar thin film materials, intense visible absorptions and their low-lying MLCT excited states which yield detectable emissions in the red region of the spectrum.

The photophysical properties of the complexes CpRe(CO)2(3-benzoylpyridine) and CpRe(CO)3(4-benzoylpyridine) are determined by examining their electronic absorption, emission and excitation spectra ans emission lifetimes. The results show that CpRe(CO)2(3-benzoylpyridine) exhibits multiple emission from triplet-centered n,pi* intraligands and metal-to-ligand charge-transfer (MLCT) levels while CpRe(CO)2(4-benzoylpyridine) exhibits only one emission spectra which is assigned to the lowest energy MLCT state. The difference were attributed to the electronic and geometric differences in the excited states.

A study was done on the pathways for photosubstitution and C-H/Si-H bond activation reactions in (n super 5-C5R5)Rh(CO)2(R=H,Me) complexes. It was shown that photoreactions involving the solutions involve clean and complete conversion to the corresponding CpRh(CO)PR3 and Cp*Rh(CO)PR3 products. The reactions occur from ligand field excited states and ligand photosubstitution proceed through an associative mechanism.

The quantitative photochemistry of Cp'Pt(CH3)(sub 3) (Cp' = eta(super 5)-C5H4CH3) in solution has been investigated. The photoefficiencies indicate that the qualitative photochemistry is 2 orders of magnitude higher than previously recognized.

Wavelength-dependent photochemistry of W(CO)4(ethylenediamine) was analyzed through a substitution reaction designed to replace the CO group with a ligand. Results of the substitution reaction analysis indicate that the quantum yield of the substituted tungsten ethylenediamine is determined by the excitation wavelength. This indicate that photosubstitution in the ligand field is achieved through a different photophysical pathway and that this reduces the efficiency of the photoreaction.

Solution photochemistry of C-H bond activation reactivity of (HBPz*3)Rh(CO)2 (Pz* = 3,5-dimethylpyrazolyl) complex in hydrocarbon solution reveals that wavelength of light excitation influences the C-H bond activation process. Different reactivities are observed in the two electronically excited states of the complex. An eta 3 to eta 2 ligand dichelation mechanism accounts for the photoinertness of the lower energy level. C-H bond activation is high in the upper energy excited state, indicating CO dissociation as the first step in the oxidative addition mechanism.

Research has been conducted on luminescent anion receptors. The authors report the development of these receptors containing ruthenium(I) tricarbonyl signaling units and amide-type anion binding site.

It is stated the photo chemistry of the [CpFe(Eta(super 6)-arene)] x system were investigated in several different solvents at 293K as a function of excitation wavelength at 355,458,488,514,633 and 683nm, The results illustrated that the photoreaction was extremely efficient in the uv and visible regions, particularly if polar solvents were employed.

A series of molecular squares with the general molecular formula [fac-Br (Co) 3Re(u- (pyterpy)(sub 2) M)](sub 4)(PF6)(sub 8), where pyterpy is 4'-(4''' - pyridyl)-2,2': 6E, 2EE -terpyridine and M=Fe, Ru, or Os are prepared. The spectroscopic properties and a preliminary anion binding study of these novel octanuclear molecular squares are studied.

A study concerning the preparation of the luminescent rhenium(I)-based molecular triangle and square complexes is presented. The associated photophysical data are described.

Self assembly triangular and square rhenium(I) tricarbonyl compounds were prepared.

Two structurally simple and easily synthesized luminescent anion receptors featured with an amide-type anion binding site and rhenium(I) tricarbonyl pyridine signaling units have been developed, and they display outstanding sensitivity and selectivity toward a variety of anionic species. These complexes are highly emissive in solution. Upon anion binding, the emission intensity was significantly quenched. The sensitivities of these complexes are so high that the emission intensity can be effectively quenched by as much as 10% even in the presence of only 10[sub -8] M cyanide or fluoride anions. The ability of formation of intramolecular hydrogen bonding between the amide protons and central pyridine is believed to be responsible for the observed high selectivity. [ABSTRACT FROM AUTHOR]

Investigates a series of heterometallic square complexes prepared by self-assembly. Molecular structures of the complexes with terpyridyl metal complexes as bridging ligands; Multiple redox processes; Metal-to-ligand charge transfer; Band structure; Luminescence; Electrochemical and photophysical properties.

Examines the preparation of self-assembly triangular and square rhenium(I) tricarbonyl complexes. Dependence of the macrocyclic complex geometries on length and bonding angles of the bridging ligands; Mechanism of the self-assembly process; Photophysical properties of the complex; Observation on the energy transfer mechanism.

Studies the thermal chemistry and photochemistry of the intermolecular C-H bond activating a rhenium organometallic complex in various alkane solutions at 293 K. Nature of electronically excited states; Photochemical C-H bond activation; Photochemical Si-H bond activation; Photophysical interpretation.

The quantitative photochemistry of the platinum organometallic complex, Cp'Pt(CH3)3 (Cp' = η5-C5H4CH3), has been investigated in methylcyclohexane and n-pentane solutions at 293 K following UV irradiation into the lowest lying absorption bands. Absolute photochemical quantum efficiency (φcr) results obtained for Cp'Pt(CH3)3 at 313 and 366 nm reveal that the system very effectively photoreacts with φcr = 0.34-0.41 in these solvents and 0.79-0.85 when 53 mM Et3SiH is incorporated. These photoefficiencies indicate that the quantitative photochemistry is 2 orders of magnitude higher than previously recognized. The application of Cp'Pt(CH3)3 as an effective photoinitiator for hydrosilylation reactions involving vinyl/hydride silicone mixtures is demonstrated. [ABSTRACT FROM AUTHOR]

Examines the self-assembly of luminescent molecular triangle and square rhenium(I) complexes. Synthesis of molecular squares; Existence of the supramolecular species in an equilibrium mixture; Preparation and characterization of self-assembled complexes; Effects of entropy on the formation of molecular triangle.

The article presents a study which investigates the determination of the quantum efficiency for activation of an organometallic photoinitiator for cationic polymerization. The study involves the measurement of photochemical efficiency for arene displacement from a mixed-sandwich compound of iron. The progress of the photochemical reaction was monitored by following the formation of the orange product using a diode-array ultraviolet-vis spectrometer. The results indicated that the irradiation wavelength cannot be assumed in calculating the quantum yield that all the absorbed photons are absorbed by the reactant.

With increasing concerns over environmental impact and overall health of both the environment and its people, a need to quantify contaminants is of the utmost importance. Chemosensors with low detection limits and a relative ease of application can address this challenge. Nitrite ions are known to be detrimental to both the environment and human health. A new colorimetric chemodosimeter has been prepared from the homolytic photochemical cleavage of a reaction between pyrrole and pyridine. The product, 4-(pyrrol-1-yl)pyridine, yields a limit of detection of 0.330 (±0.09) ppm for the detection of nitrite in aqueous solution, employing a colorimetric change from yellow to pink. It is also highly selective for nitrite when various competitive anions such as SO 3 2- , NO 3 - , PO 4 3- , SO 4 -2 , Cl - , F - , I - , Br - , AcO - , and CN - are present in great excess. The molecule's especially high sensitivity to nitrite is apparently the result of a complex supramolecular mechanism, characterized by both dynamic light scattering of the aggregate and the Tyndall effect. Consequently, this new sensor provides a simple, low-cost way to rapidly detect nitrite anions in aqueous solution., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The quantitative photochemistry of the platinum organometallic complex, Cp'Pt(CH(3))(3) (Cp' = eta(5)-C(5)H(4)CH(3)), has been investigated in methylcyclohexane and n-pentane solutions at 293 K following UV irradiation into the lowest lying absorption bands. Absolute photochemical quantum efficiency (phi(cr)) results obtained for Cp'Pt(CH(3))(3) at 313 and 366 nm reveal that the system very effectively photoreacts with phi(cr) = 0.34-0.41 in these solvents and 0.79-0.85 when 53 mM Et(3)SiH is incorporated. These photoefficiencies indicate that the quantitative photochemistry is 2 orders of magnitude higher than previously recognized. The application of Cp'Pt(CH(3))(3) as an effective photoinitiator for hydrosilylation reactions involving vinyl/hydride silicone mixtures is demonstrated.

The quantitative photochemistry of (eta(5)-C(5)H(5))Fe(CO)(2)I in room-temperature solution involving the heterolytic cleavage of iodide to form (eta(5)-C(5)H(5))Fe(CO)(2)(eta(1)-N-pyrrolyl) has been investigated following irradiation at several wavelengths in the 488-647 nm region. The most effective photoconversions were found to take place with excitation at long wavelengths (580-647 nm) into weak low-lying absorption bands; the absolute quantum efficiency for the photoreaction of (eta(5)-C(5)H(5))Fe(CO)(2)I in room-temperature toluene has been determined to be 0.38 (+/-0.02) upon Kr(+) laser photolysis at 647 nm. The photochemical results are in accordance with recent assignments for the HOMO orbitals in (eta(5)-C(5)H(5))Fe(CO)(2)I and demonstrate that long-wavelength irradiation provides a valuable way of effecting heterolytic Fe-I dissociation, facilitating a synthetic pathway to azaferrocene.

The photochemically-induced intermolecular C-H bond activation reaction of (HBPz'(3))Rh(CO)(2) (Pz' = 3,5-dimethylpyrazolyl) has been investigated in various hydrocarbon solutions at 293 K following excitation at 366 and 458 nm. UV-visible and FTIR spectra recorded throughout photolysis illustrate that the dicarbonyl complex can be converted readily to the corresponding (HBPz'(3))Rh(CO)(R)H derivatives at each of the excitation wavelengths. The photochemistry proceeds without interference from secondary photoprocesses or thermal reactions and the reactivity has been measured quantitatively with the determination of absolute quantum efficiencies for intermolecular C-H bond activation (phi(CH)). These measurements indicate that the C-H activation reaction proceeds very efficiently (phi(CH) = 0.13-0.32) on excitation at 366 nm but is much less effective (phi(CH) = 0.0059-0.011) on photolysis at 458 nm for each of the hydrocarbon substrates. The observed dependence of phi(CH) on irradiation wavelength is consistent with different reactivities from two rapidly dissociating low-energy ligand field (LF) excited states and the generation of monocarbonyl (HBPz'(3))Rh(CO) and ligand-dechelated (eta(2)-HBPz'(3))Rh(CO)(2) intermediates upon UV and visible excitation, respectively. The former species is attributed to be responsible for the unusually efficient C-H bond activation, whereas it is suggested that the latter complex effectively lowers the quantum efficiency by undergoing a facile eta(2)-->eta(3) ligand rechelation process. Significantly, the photoefficiencies are found to be unaffected on increasing the dissolved CO concentration, illustrating that the monocarbonyl reaction intermediate is extremely short-lived and is solvated before CO is able to coordinate. Additionally, the lack of a [CO] dependence on phi(CH) indicates that this solvated intermediate is not subject to a competitive back-reaction with CO prior to the C-H activation step, illustrating that the quantum efficiencies in (HBPz'(3))Rh(CO)(2) appear to be solely determined by the branching ratio between the dissociative and nondissociative routes. At any particular excitation wavelength the photoefficiencies are observed to be similar across the series of alkanes but are significantly reduced for the aromatic solvents, even though the aryl hydrido photoproducts are found to be more thermodynamically stable. These phi(CH) differences are also rationalized in terms of photophysical effects on the upper LF level and are related to variations in the nonradiative relaxation rates for the excited (HBPz'(3))Rh(CO)(2) complex in the hydrocarbon solutions.