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Despite their versatile synthetic utility, vinyl azides have complex and poorly understood photochemistry. To address this, we investigated the photoreactivity of 1-azidostyrene 1 and 3-phenyl-2H-azirine 2 in solution and cryogenic matrices. In argon matrices, irradiation of 1 at 254 nm yielded 2, phenyl nitrile ylide 3, and N-phenyl ketenimine 4, whereas irradiation at wavelengths above 300 nm produced only 2 and 4. Similarly, irradiation of 1 in 2-methyltetrahydrofuran (mTHF) glass at 77 K mainly yielded absorption corresponding to the formation of 2 (λmax ~ 252 nm). In contrast, irradiation of 2 at wavelengths above 300 nm in Argon matrices yielded no photoproducts, whereas irradiation at 254 nm resulted in the formation of 3. Furthermore, femto- and nanosecond transient absorption and laser flash photolysis were performed to ascertain the transient species and reactive intermediates formed during the photochemical transformations of 1 and 2. The ultrafast transient absorption spectroscopy of 1 resulted in a transient absorption band centered at ca. 472 nm with a time constant τ ~ 22 ps, which was assigned to the first singlet excited state (S1) of 1. The nano-second flash photolysis of 1 (308 nm laser) generated 2 within the laser pulse (~17 ns), and subsequently 2 is excited to yield triplet vinylnitrene 31N with an absorption centered at ~ 440 nm. In contrast, the nano-second laser flash photolysis of 2 with 266 nm laser produced a weak absorption corresponding to 3, whereas 308 nm laser yielded absorption due to triplet vinylnitrene 31N (λmax ~ 440 nm). These findings demonstrate that the direct irradiation of 1 populates S1 of 1, which does not intersystem cross to form 31N, but instead decays to yield 2. Density functional theory calculations supported the characteristics of the excited states and reactive intermediates formed upon irradiation of 1 and 2.
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Unraveling the Solid-State Photoreactivity of Carbonylbis(4,1-Phenylene)dicarbonazidate with Laser Flash Photolysis
Solid-state photoreactions are generally controlled by the rigid and ordered nature of crystals. Herein, the solution and solid-state photoreactivities of carbonylbis(4,1-phenylene)dicarbonazidate (1) were investigated to elucidate the solid-state reaction mechanism. Irradiation of 1 in methanol yielded primarily the corresponding amine, whereas irradiation in the solid state gave a mixture of photoproducts. Laser flash photolysis in methanol showed the formation of the triplet ketone (TK) of 1 (τ ∼ 99 ns), which decayed to triplet nitrene 31N (τ ∼ 464 ns), as assigned by comparison to its calculated spectrum. Laser flash photolysis of a nanocrystalline suspension and diffuse reflectance laser flash photolysis also revealed the formation of TK of 1 (τ ∼ 106 ns) and 31N (τ ∼ 806 ns). Electron spin resonance spectroscopy and phosphorescence measurements further verified the formation of 31N and the TK of 1, respectively. In methanol, 31N decays by H atom abstraction. However, in the solid state, 31N is sufficiently long lived to thermally populate its singlet configuration (11N). Insertion of 11N into the phenyl ring to produce oxazolone competes with 31N cleavage to form a radical pair. Notably, 1 did not exhibit photodynamic behavior, likely because the photoreaction occurs only on the crystal surfaces.
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- Award ID(s):
- 2102248
- PAR ID:
- 10476801
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry A
- Volume:
- 127
- Issue:
- 46
- ISSN:
- 1089-5639
- Page Range / eLocation ID:
- 9705 to 9716
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.jpca.3c04867
