Photochemistry of Azides: The Azide/Nitrene Interface

Gritsan, Nina P.; Platz, Matthew S.

doi:10.1002/9780470682517.ch11

Cited by 48 publications

(78 citation statements)

References 244 publications

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“…We prefer the triplet nitrene as our tentative assignment since observations of benzazirines are quite rare. 41b,c Moreover, as mentioned previously, it seems reasonable to expect that an ortho methoxy group to accelerate ISC in a manner similar to that of a para methoxy group 9 .…”

Section: Resultsmentioning

confidence: 67%

“…In this interpretation, the ISC rate for 4b must be much faster than the ISC rate of parent phenylnitrene (3.2×10 6 s −1 ), 2 determined at low temperature, and comparable to that found previously with 4-methoxyphenylnitrene, which was estimated to be greater than 5×10 8 s −1 by laser flash photolysis measurements. 9 We propose that the 2-methoxy group promotes a large acceleration of the ISC rate as it increases the zwitterionic character of the singlet nitrene relative to the parent system, which facilitates a spin-orbit coupling mechanism of ISC. 54 …”

Section: Resultsmentioning

confidence: 95%

“…This interpretation postulates that the 2-methoxy group accelerates the ISC rate relative to unsubstituted singlet phenylnitrene 2 , in the same manner as does a para -methoxy substituent. 9 …”

Section: Resultsmentioning

confidence: 99%

“…For example, a substituent at the para position, especially an electron-donating group can dramatically increase the ISC rate. 9 …”

Section: Introductionmentioning

confidence: 99%

“…9 A single ortho substituent usually has little influence on the rate of singlet phenylnitrene isomerization to the azirine. Singlet 2-methylphenylnitrene, at room temperature has a 1 ns lifetime, 1 the same as that of the parent singlet phenylnitrene.…”

Section: Introductionmentioning

confidence: 99%

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Ultrafast Infrared and UV–Vis Studies of the Photochemistry of Methoxycarbonylphenyl Azides in Solution

et al. 2012

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The photochemistry of 4-methoxycarbonylphenyl azide (2a), 2-methoxycarbonylphenyl azide (3a) and 2-methoxy-6-methoxycarbonylphenyl azide (4a) were studied by ultrafast time-resolved infrared (IR) and UV-vis spectroscopies in solution. Singlet nitrenes and ketenimines were observed and characterized for all three azides. Isoxazole species 3g and 4g are generated after photolysis of 3a and 4a, respectively, in acetonitrile. Triplet nitrene 4e formation correlated with the decay of singlet nitrene 4b. The presence of water does not change the chemistry or kinetics of singlet nitrenes 2b and 3b, but leads to protonation of 4b to produce nitrenium ion 4f. Singlet nitrenes 2b and 3b have lifetimes of 2 ns and 400 ps, respectively, in solution at ambient temperature. The singlet nitrene 4b in acetonitrile has a lifetime of about 800 ps, and reacts with water with a rate constant of 1.9 × 108 L·mol−1·s−1 at room temperature. These results indicate that a methoxycarbonyl group at either the para or ortho positions has little influence on the ISC rate, but that the presence of a 2-methoxy group dramatically accelerates the ISC rate relative to the unsubstituted phenylnitrene. An ortho methoxy group highly stabilizes the corresponding nitrenium ion and favors its formation in aqueous solvents. This substituent has little influence on the ring-expansion rate. These results are consistent with theoretical calculations for the various intermediates and their transition states. Cyclization from the nitrene to the azirine intermediate is favored to proceed towards the electron-deficient ester group; however, the higher energy barrier is the ring-opening process, that is azirine to ketenimine formation, rendering the formation of the ester-ketenimine to be less favorable than the isomeric MeO-ketenimine.

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Section: Resultsmentioning

confidence: 67%

Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

“…For example, a substituent at the para position, especially an electron-donating group can dramatically increase the ISC rate. 9 …”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ultrafast Infrared and UV–Vis Studies of the Photochemistry of Methoxycarbonylphenyl Azides in Solution

et al. 2012

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Photogeneration of Carbenes and Nitrenes

2013

Photochemically‐Generated Intermediates in Synthesis

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Photo‐Crosslinkable Unnatural Amino Acids Enable Facile Synthesis of Thermoresponsive Nano‐ to Microgels of Intrinsically Disordered Polypeptides

et al. 2017

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Hydrogel particles are versatile materials that provide exquisite, tunable control over the sequestration and delivery of materials in pharmaceutics, tissue engineering, and photonics. The favorable properties of hydrogel particles depend largely on their size, and particles ranging from nanometers to micrometers are used in different applications. Previous studies have only successfully fabricated these particles in one specific size regime and required a variety of materials and fabrication methods. A simple yet powerful system is developed to easily tune the size of polypeptide-based, thermoresponsive hydrogel particles, from the nano- to microscale, using a single starting material. Particle size is controlled by the self-assembly and unique phase transition behavior of elastin-like polypeptides in bulk and within microfluidic-generated droplets. These particles are then stabilized through ultraviolet irradiation of a photo-crosslinkable unnatural amino acid (UAA) cotranslationally incorporated into the parent polypeptide. The thermoresponsive property of these particles provides an active mechanism for actuation and a dynamic responsive to the environment. This work represents a fundamental advance in the generation of crosslinked biomaterials, especially in the form of soft matter colloids, and is one of the first demonstrations of successful use of UAAs in generating a novel material.

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Photochemistry of Azides: The Azide/Nitrene Interface

Cited by 48 publications

References 244 publications

Ultrafast Infrared and UV–Vis Studies of the Photochemistry of Methoxycarbonylphenyl Azides in Solution

Ultrafast Infrared and UV–Vis Studies of the Photochemistry of Methoxycarbonylphenyl Azides in Solution

Photogeneration of Carbenes and Nitrenes

Photo‐Crosslinkable Unnatural Amino Acids Enable Facile Synthesis of Thermoresponsive Nano‐ to Microgels of Intrinsically Disordered Polypeptides

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