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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.