Stable Room Temperature Nitrenes Created by Photolysis of Crystalline 4-Azido-2,3,5,6-tetrafluorobenzoic Acid

Abstract

The structure, spectroscopy, and photochemistry of 4-azidobenzoic acid (4ABC) and its perfluorinated analog 4-azido-2,3,5,6-tetrafluorobenzoic acid (4F4ABC) are characterized in frozen glasses and crystals. Photolysis of the parent azides leads to the production of nitrenes and other spin species that are probed by electron paramagnetic resonance and optical spectroscopy. Shifts in the absorption spectra for both the parent azides and the nitrenes were well reproduced using density functional calculations. Photolysis generates ∼10× higher yield of the triplet nitrene relative to the quintet and radical side-products in 4F4ABC, while the opposite ratio is observed in 4ABC. An annealing step further suppressed the side-products in 4F4ABC, creating a solid where nitrenes were the dominant spin species. The nitrene in the 4F4ABC crystal has a 1/e lifetime of 20 days at room temperature in open air. This stability makes it possible to photopattern nitrene centers into a single crystal and characterize their photoluminescence. Multiple observations suggest that the remarkable stability in the 4F4ABC crystal is a consequence of crystal packing that traps N2 molecules adjacent to the nitrene. The ability to create stable, solid-state nitrene samples may provide a route to organic high-spin materials with potential applications in spintronics and quantum information science.

Recent advances in the chemistry of isolable carbene analogues with group 13–15 elements

“…343,344 The generation of nitrenes often results from the thermal or photochemical decomposition of entities like hydrazoic acid and organic azides. [345][346][347][348] The electronic characteristics of a nitrene, including the singlet-triplet energy gap, and consequently its stability and reactivity, are influenced by its substituent. Around 1980s, Dervan and Roberts elucidated the synthesis and characterization of singlet aminonitrenes 142 and 143 (Fig.…”

Alternant Hydrocarbon Diradicals as Optically Addressable Molecular Qubits

“…In the most extreme case, the π-diradical may have no closed-shell Kekulé structures at all; such molecules are termed “non-Kekulé,” , and an example has been shown in Figure c. However, this analysis is purely qualitative, and there exist non-Kekulé molecules with appreciable closed-shell characters (interestingly, alkaline earth metal complexes, commonly used as optical cycling centers, , as well as nitrenes have also been investigated for luminescent diradical properties and are useful candidates of molecular color centers as well).…”