Effect of Iodination on the Photophysics of the Laser Borane anti-B₁₈H₂₂: Generation of Efficient Photosensitizers of Oxygen

Abstract

Treatment of the laser borane anti-B18H22 (compound 1) with iodine in ethanol gives the monoiodinated derivative 7-I-anti-B18H21 (compound 2) in 67% yield, or, by reaction with iodine or ICl in the presence of AlCl3 in dichloromethane, the diiodinated derivative 4,4′-I2-anti-B18H20 (compound 3) in 85% yield. On excitation with 360 nm light, both compounds 2 and 3 give strong green phosphorescent emissions (λmax = 525 nm, ΦL = 0.41 and λmax = 545 nm, ΦL = 0.71 respectively) that are quenched by dioxygen to produce O2(1Δg) singlet oxygen with quantum yields of ΦΔ = 0.52 and 0.36 respectively. Similarly strong emissions can be stimulated via the nonlinear process of two-photon absorption when exciting with 720 or 800 nm light. The high quantum yields of singlet-oxygen production, coupled with the option of two-photon excitation, make compounds 2 and 3 promising O2(1Δg) photosensitizers. The molecular structures of compounds 2 and 3 were determined by single-crystal X-ray crystallographic studies as well as multinuclear NMR spectroscopy and mass spectrometry. Time-resolved UV–vis spectroscopy was used to delineate their photophysical properties, and the electronic-structure properties of the emitting species were determined by means of multiconfigurational quantum-chemistry computations.

Photochromic System among Boron Hydrides: The Hawthorne Rearrangement

“…Access to innovative and/or more efficient technological devices is directly linked to the development of usable functionalized materials such as responsive molecular switches. , Therefore, the growing needs of industry demand a systematic exploration of molecules displaying attractive photophysical and photochemical properties, requiring the fine understanding at a fundamental level of the molecular mechanisms that govern the photoprocesses coming into play. In this framework, boron hydrides − represent a family of compounds whose rich structural variety offers a diverse set of tunable optical properties with potential applications such as blue lasing, , strongly phosphorescent luminophores, singlet oxygen production, and energy-transfer composite materials . Other borane-based large systems have recently emerged as appealing materials for medicinal applications, whereas the functionalization of icosahedral boranes, carboranes, and metallacarboranes has a growing interest as alternatives to the traditional organic and organometallic material building blocks .…”

“…Future works may optimize the optical properties of the switch; for instance, the UV absorption could be red-shifted by deriving the cluster with pyrimidine ligands or sulfur or iodine atoms, strategies that significantly shift the absorption maxima of the related boron laser prototype anti -B 18 H 22 . On the other hand, the photo/thermal conversions could be optimized by decreasing the response speed via structural modifications that displace the CI toward the photoproducts and/or decrease the energy barrier of the thermal conversion.…”

A Series of Ultra-Efficient Blue Borane Fluorophores

“…These are all factors of general practical benefit regarding the fabrication of optical devices. The photophysics of compound 1 may be modified by the introduction of substituents or ligands to replace the terminal hydrogen atoms on the cluster such as −SH, bromine, iodine, and pyridine , to give molecules capable of, for example, environmentally sensitive thermochromic luminescence, single-molecule multiple emissions, and the photosensitization of oxygen . In addition, the optical properties of the parent compound have been shown to tolerate dissolution in aqueous micelles , in work that has been recently patented .…”

The UV photodegradability study of octadecaborane in polystyrene matrix thin films

“…Besides molecules and polymers with πor σ-electron delocalisation, borane clusters may become a new class of electronic materials based on electron delocalisation due to electron-deficient multicentre bonds. The primary attention is paid to cage boron-hydride derivatives with blue luminescence emission located near 400 nm, in particular anti-B18H22, whose emission was reported as stable [8].…”