Photoinduced Charge‐Transfer State of 4‐Carbazolyl‐3‐(trifluoromethyl)benzoic Acid: Photophysical Property and Application to Reduction of Carbon−Halogen Bonds as a Sensitizer

Matsubara, Ryosuke; Shimada, Toshiyuki; Kobori, Yasuhiro; Yabuta, Tatsushi; Osakai, Toshiyuki; Hayashi, Masahiko

doi:10.1002/asia.201600538

Cited by 18 publications

(12 citation statements)

References 52 publications

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“… a) Working hypothesis of phototriggered nitrile formation. b) Inspiring findings reported in our previous study …”

Section: Figuresupporting

confidence: 68%

“…The thus‐formed iminyl cation would then undergo a deprotonation, leading to the nitrile group. Previously, we have observed a fast BET from the carbon radical to the radical cation of carbazole derivative 1 (Scheme b) . Considering these previous findings, we expected that, in analogy to the carbon radical, the iminyl radical would undergo a BET with a suitable carbazole‐based photosensitizer rapidly enough to compete with the other radical reactions involved with the iminyl radical.…”

Section: Figurementioning

confidence: 82%

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Photoinduced Nitrile Formation from O‐(Arylcarbonyl) oxime: Usage as a Photoremovable Protecting Group

et al. 2018

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Employing a photoremovable protecting group is a useful technique to achieve precise conditional control over a biological function. This Communication reports the development of a photoremovable protecting group for the nitrile moiety. In the process, O-(arylcarbonyl) oxime was photochemically converted into the corresponding nitrile in the presence of a carbazole photosensitizer by means of an electron transfer from the excited carbazole to the arylcarbonyl unit. A variety of alkyl and (hetero) aryl nitriles were generated from the corresponding O-(arylcarbonyl) oximes. Moreover, a self-contained variant, in which O-(arylcarbonyl) oxime and carbazole units were covalently bonded, exhibited photochemical nitrile formation even in a highly diluted aqueous solution (0.1 mM), thus demonstrating that this molecular motif is potentially applicable in biological systems.[a] Prof.

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“… a) Working hypothesis of phototriggered nitrile formation. b) Inspiring findings reported in our previous study …”

Section: Figuresupporting

confidence: 68%

Section: Figurementioning

confidence: 82%

Photoinduced Nitrile Formation from O‐(Arylcarbonyl) oxime: Usage as a Photoremovable Protecting Group

et al. 2018

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“…Previously, we reported that a 3,6-dimethoxycarbazole derivative (CAR3, Scheme 1), which has an electron-deficient aryl substituent on the carbazole nitrogen, could catalyze the photochemical dehalogenation of unactivated primary alkyl bromides. 10 The fact that carbazole CAR3 showed higher reducing ability than CAR2 (Scheme 1) was rationalized by assuming that the charge-transfer (CT) excited state of CAR3 effectively suppresses back electron transfer. However, the CAR3 could not reduce some of the more demanding substrates, such as aryl bromides and organochlorides.…”

Section: Resultsmentioning

confidence: 99%

“…(3) The ideal PC should absorb photons at wavelengths longer than 350 nm to avoid unwanted direct excitation of substrates and allow the utilization of the UVA and visible-light region of sunlight. (4) Based on our previous finding, 10 the CT excited state helps to retard the unproductive back electron transfer. 12 DFT calculations for the parent molecule (carbazole) showed large orbital coefficients at C3 and C6 in the HOMO, while nodes exist on these two carbons in the lowest unoccupied molecular orbital (LUMO) (Figure 2).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

UVA- and Visible-Light-Mediated Generation of Carbon Radicals from Organochlorides Using Nonmetal Photocatalyst

et al. 2018

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Carbon radicals are reactive species useful in various organic transformations. The C-X bond cleavage of organohalides by photoirradiation is a common method to generate carbon radicals in a controlled fashion. The use of organochloride substrates is still a formidable challenge due to the low reduction potential and the high dissociation energy of the C-Cl bond. In this report, we address these issues by using a nonmetal organic molecule with a relatively simple structure as a photocatalyst. In this catalyst (bis(dimethylamino)carbazole), the amino groups increase both the HOMO and LUMO energy levels, especially in the former. As a result, compared to the parent molecule, the new catalyst shows experimentally red-shifted absorption in the visible region and forms an excited state with better reducing capability. This photocatalyst was used in the reduction of unactivated aryl chlorides and alkyl chlorides in the presence of hydrogen atom donor at room temperature. The catalytic system can also be applied to the coupling of aryl chlorides with electron-rich arene and heteroarenes to affect the C-C bond-forming reactions. Our mechanistic study results support the assumption that carbon radicals are formed from the organochlorides via a single-electron-transfer step.

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“…Our laboratory has been focusing on the development of nonmetal PCs with high reducing ability . We observed that the carbazole-based visible-light-activated PC PC1 , bearing excited-state oxidation potentials as negative as −2.75 V versus SCE, exhibited high catalytic performance, enabling the reduction of unactivated chloroarenes ( E red [PhCl/PhCl •– ] = −2.88 V vs SCE) and even a fluoroarene via the SET mechanism. − The installation of dimethylamino groups at the carbazole 3- and 6-positions provided two advantages: (1) A 40 nm bathochromic shift over that of PC2 in the absorption spectrum, enabling visible-light activation and (2) increased excited-state reducing ability [ E ox * = −2.75 V ( PC1 ) versus −2.47 V ( PC2 )].…”

Section: Introductionmentioning

confidence: 99%

Photocatalytic Reductive C–O Bond Cleavage of Alkyl Aryl Ethers by Using Carbazole Catalysts with Cesium Carbonate

2021

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Methods to activate the relatively stable ether C–O bonds and convert them to other functional groups are desirable. One-electron reduction of ethers is a potentially promising route to cleave the C–O bond. However, owing to the highly negative redox potential of alkyl aryl ethers (E red < −2.6 V vs SCE), this mode of ether C–O bond activation is challenging. Herein, we report the visible-light-induced photocatalytic cleavage of the alkyl aryl ether C–O bond using a carbazole-based organic photocatalyst (PC). Both benzylic and non-benzylic aryl ethers underwent C–O bond cleavage to form the corresponding phenol products. Addition of Cs2CO3 was beneficial, especially in reactions using a N–H carbazole PC. The reaction was proposed to occur via single-electron transfer (SET) from the excited-state carbazole to the substrate ether. Interaction of the N–H carbazole PC with Cs2CO3 via hydrogen bonding exists, which enables a deprotonation-assisted electron-transfer mechanism to operate. In addition, the Lewis acidic Cs cation interacts with the substrate alkyl aryl ether to activate it as an electron acceptor. The high reducing ability of the carbazole combined with the beneficial effects of Cs2CO3 made this otherwise formidable SET event possible.

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Photoinduced Charge‐Transfer State of 4‐Carbazolyl‐3‐(trifluoromethyl)benzoic Acid: Photophysical Property and Application to Reduction of Carbon−Halogen Bonds as a Sensitizer

Cited by 18 publications

References 52 publications

Photoinduced Nitrile Formation from O‐(Arylcarbonyl) oxime: Usage as a Photoremovable Protecting Group

Photoinduced Nitrile Formation from O‐(Arylcarbonyl) oxime: Usage as a Photoremovable Protecting Group

UVA- and Visible-Light-Mediated Generation of Carbon Radicals from Organochlorides Using Nonmetal Photocatalyst

Photocatalytic Reductive C–O Bond Cleavage of Alkyl Aryl Ethers by Using Carbazole Catalysts with Cesium Carbonate

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