Direct Observation of Acyl Azide Excited States and Their Decay Processes by Ultrafast Time Resolved Infrared Spectroscopy

Kubicki, Jacek; Zhang, Yunlong; Luk, Hoi Ling; Peng, Huo Lei; Vyas, Shubham; Platz, Matthew S.

doi:10.1021/ja9002102

Cited by 41 publications

(87 citation statements)

References 16 publications

(27 reference statements)

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“…As there is considerable difference in the character of the lowest singlet excited states of these two sets of acyl azides, these compounds may have different photochemical channels leading to different products. However, as previously shown, excitation with 270‐nm light for both PhCON 3 and 2‐NpCON 3 in chloroform leads to the formation of the corresponding isocyanate and singlet aroylnitrene, suggesting similar photochemical behavior of these two acyl azides. The calculated difference density plots and the vertical excitation energies (Table ) suggest differences in the excited state ordering.…”

Section: Computational Resultssupporting

confidence: 71%

“…In our short communication, results from our initial ultrafast fs TRIR study on the photochemistry of t ‐BuCON 3 , PhCON 3 , and 2‐NpCON 3 (with 270 nm excitation, in chloroform) were reported . Formation of aroylnitrenes and isocyanates was detected at 1760 and 2265 cm −1 , respectively .…”

Section: Ultrafast Trir and Uv–vis Pump‐probe Absorption Measurementsmentioning

confidence: 92%

“…Another positive band observed at 2100 cm −1 was assigned to the S 1 state of the acyl azides. The latter band decays bi‐exponentially (e.g., τ 1 = 6.8 ± 1.3 and τ 2 = 116 ± 30 ps for 2‐NpCON 3 in chloroform), and the fast component was attributed to the hot S 1 state . The relatively long component was assigned to the thermally relaxed S 1 state of acyl azides .…”

Section: Ultrafast Trir and Uv–vis Pump‐probe Absorption Measurementsmentioning

confidence: 99%

“…In this paper, we report results of ultrafast TRIR and UV–vis studies on the photochemistry of PhCON 3 , p ‐BpCON 3 , 2‐AnCON 3 , and t ‐BuCON 3 (Chart 1) in chloroform and in acetonitrile, along with density functional theory (DFT) calculations. TRIR data for PhCON 3 and t ‐BuCON 3 in chloroform were published recently, and they are presented here for comparison. All of our experimental findings are consistent with the predictions made by DFT calculations.…”

Section: Introductionmentioning

confidence: 99%

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An ultrafast time‐resolved infrared and UV–vis spectroscopic and computational study of the photochemistry of acyl azides

Vyas

Kubicki

Luk

et al. 2012

J of Physical Organic Chem

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The photochemistry of pivaloyl, benzoyl, 4‐phenylbenzoyl, and 2‐anthroyl azides has been studied using femtosecond (fs) time‐resolved infrared (TRIR) and UV–vis spectroscopy and interpreted with the aid of computational chemistry. Density functional theory calculations revealed a significant difference in the nature of the lowest singlet excited state for these carbonyl azides. The lowest singlet excited states (S1) of p‐phenylbenzoyl and 2‐anthroyl azides are (π,π*) in nature, while the pivaloyl and benzoyl azides S1 states involve (n,π*) excitations. Nevertheless, for all acyl azides studied here, a similar, and intense, IR band at about 2100 cm−1 has been detected in the ultrafast TRIR experiments following 270 nm excitation. These bands were shifted to lower energy by about 100 cm−1 relative to the N3 stretching mode for the ground states of these azides. These 2100 cm−1 vibrational bands were assigned to the S1 states of acyl azides in agreement with density functional theory calculations. The decay of the acyl azide S1 states was described by bi‐exponential functions. The fast component was attributed to the decay of the hot S1 state and the longer component to the decay of the thermally relaxed S1 state. A strong and broad transient absorption in the 350–650 nm spectral range was observed in the fs UV–vis experiments for p‐phenylbenzoyl and 2‐anthroyl azides. The carrier of this absorption also decayed bi‐exponentially, and the time constants were in excellent agreement with those found in the fs TRIR experiments. The slow component of the S1 state decay was found to be dependent on the solvent polarity. When the lifetime of the acyl azide S1 state is substantially longer than the time constant for vibrational cooling of nascent (hot) isocyanate, the correlation between the S1 decay and isocyanate formation was clear. The 270 nm excitation populates the Sn (n ≥ 2) states of these acyl azides. It was established that a hot nitrene is produced more efficiently from both the Sn and hot S1 states than from the relaxed S1 state of these acyl azides. Thus, time‐resolved study provides direct experimental evidence that the S1 state is the precursor of nitrene only when the S1 state is pumped directly and when the S1 state lifetime is longer than the time constant of vibrational cooling of the newborn nitrene. All of these results are consistent with the data obtained recently for 2‐napththoyl azide. Copyright © 2012 John Wiley & Sons, Ltd.

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Section: Computational Resultssupporting

confidence: 71%

Section: Ultrafast Trir and Uv–vis Pump‐probe Absorption Measurementsmentioning

confidence: 92%

Section: Ultrafast Trir and Uv–vis Pump‐probe Absorption Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An ultrafast time‐resolved infrared and UV–vis spectroscopic and computational study of the photochemistry of acyl azides

Vyas

Kubicki

Luk

et al. 2012

J of Physical Organic Chem

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“…[4,5] Of particular interest is the photodecomposition of carbonyl azides, which has been studied by time-resolved infrared spectroscopy. [6][7][8][9] Upon UV irradiation (l 250 nm), excited carbonyl azides may fragment to form two different products, carbonyl nitrenes and the Curtius-rearranged isocyanate (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

The Missing Link: Triplet Fluorocarbonyl Nitrene FC(O)N

Zeng

Beckers

Willner

et al. 2011

Chemistry A European J

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The elusive triplet fluorocarbonyl nitrene, FC(O)N (X(3 A''), has been generated in high yield from matrix-isolated FC(O)N(3) by ArF excimer laser photolysis (λ=193 nm). As a side product FNCO was formed. The novel nitrene was characterized by IR, UV/Vis, EPR spectroscopy, and quantum-chemical calculations. All six fundamental vibrations of FC(O)N at 1681.3, 1193.8, 879.8, 646.5, 588.7, and 434.8 cm(-1) (argon matrix, 16 K), their (12/13)C, (16/18)O, and (14/15)N isotopic shifts, and four electronic transitions at T(0) =13 890, 25 428, 29 166, and 30 900 cm(-1) that exhibit vibrational fine structures have been detected. Under visible-light irradiation at λ≥495 nm, FC(O)N reacted with molecular N(2) in the matrix cage at 6 K to give back FC(O)N(3), whereas near-UV irradiation at λ≥335 nm yielded FNCO. The singlet-triplet energy gaps of different carbonyl nitrenes are discussed.

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Properties of Carbonyl Nitrenes and Related Acyl Nitrenes

Gritsan

2013

Nitrenes and Nitrenium Ions

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Direct Observation of Acyl Azide Excited States and Their Decay Processes by Ultrafast Time Resolved Infrared Spectroscopy

Cited by 41 publications

References 16 publications

An ultrafast time‐resolved infrared and UV–vis spectroscopic and computational study of the photochemistry of acyl azides

An ultrafast time‐resolved infrared and UV–vis spectroscopic and computational study of the photochemistry of acyl azides

The Missing Link: Triplet Fluorocarbonyl Nitrene FC(O)N

Properties of Carbonyl Nitrenes and Related Acyl Nitrenes

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