Charge-transfer sensitization of the valence photoisomerization of norbornadiene to quadricyclene by an orthometalated transition-metal complex

Grutsch, Paul A.; Kutal, Charles

doi:10.1021/ja00271a053

Cited by 37 publications

(15 citation statements)

References 2 publications

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“…partially redox-mediated mechanism via sensitization in a charge-transfer encounter complex and successfully employed an Ir(III)-based catalyst. 104 In our case, it seems plausible that the TTET pathway is operative.…”

Section: ■ Results and Discussionmentioning

confidence: 60%

High Triplet Energy Iridium(III) Isocyanoborato Complex for Photochemical Upconversion, Photoredox and Energy Transfer Catalysis

et al. 2022

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Cyclometalated Ir(III) complexes are often chosen as catalysts for challenging photoredox and triplet−triplet-energy-transfer (TTET) catalyzed reactions, and they are of interest for upconversion into the ultraviolet spectral range. However, the triplet energies of commonly employed Ir(III) photosensitizers are typically limited to values around 2.5−2.75 eV. Here, we report on a new Ir(III) luminophore, with an unusually high triplet energy near 3.0 eV owing to the modification of a previously reported Ir(III) complex with isocyanoborato ligands. Compared to a nonborylated cyanido precursor complex, the introduction of B(C 6 F 5 ) 3 units in the second coordination sphere results in substantially improved photophysical properties, in particular a high luminescence quantum yield (0.87) and a long excited-state lifetime (13.0 μs), in addition to the high triplet energy. These favorable properties (including good long-term photostability) facilitate exceptionally challenging organic triplet photoreactions and (sensitized) triplet−triplet annihilation upconversion to a fluorescent singlet excited state beyond 4 eV, unusually deep in the ultraviolet region. The new Ir(III) complex photocatalyzes a sigmatropic shift and [2 + 2] cycloaddition reactions that are unattainable with common transition metalbased photosensitizers. In the presence of a sacrificial electron donor, it furthermore is applicable to demanding photoreductions, including dehalogenations, detosylations, and the degradation of a lignin model substrate. Our study demonstrates how rational ligand design of transition-metal complexes (including underexplored second coordination sphere effects) can be used to enhance their photophysical properties and thereby broaden their application potential in solar energy conversion and synthetic photochemistry.

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Section: ■ Results and Discussionmentioning

confidence: 60%

High Triplet Energy Iridium(III) Isocyanoborato Complex for Photochemical Upconversion, Photoredox and Energy Transfer Catalysis

et al. 2022

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“…The system has been a topic of intense interest [13][14][15][16][17][18][19], and a mechanism for the conversion from norbornadiene to quadricyclane has been proposed [7,15,[20][21][22][23][24][25][26][27][28][29]. The mechanism is shown in Figure 1 and involves two transient species with different structures.…”

Section: Introductionmentioning

confidence: 99%

Bromosubstituted norbornadienes and their reversible photolytic transformation to quadricyclanes

Sørensen

Madsen

Martin

et al. 2014

ScienceOpen Research

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Two new model systems for use within the rapidly developing ultrafast time resolved x-ray scattering techniques have been prepared. Their photoisomerisation from norbornadiene to quadricyclane was found to be a suitable reaction to follow. Simulations of scattering patterns (not included in this report) showed that if heavy atoms are included in these molecular structures, then the transformation can be followed by transient x-ray scattering techniques. Two new bromosubstituted norbornadienes were synthesised and characterised. Absorption spectroscopy showed that the norbornadienes are converted quantitatively to quadricyclanes under UV irradiation. NMR studies showed that the process was fully reversible and that the norbornadienes could be completely recovered even without addition of catalysts. Furthermore, it was shown that the formation of quadricyclane from norbornadiene was unaffected by triplet sensitizers. The two new model systems synthesised thus are strong candidates for use in time resolved x-ray scattering studies both in gas and condensed phases.

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“…The mechanism of valence isomerization of norbornadiene to quadricyclane has been extensively studied . Triplet sensitization of norbornadiene generates its triplet state, 3 NB, which undergoes adiabatic isomerization to the triplet state of quadricyclane, 3 Q, which very rapidly decays to its ground state, Scheme …”

Section: Introductionmentioning

confidence: 99%

Bond-Coupled Electron Transfer Reactions: Photoisomerization of Norbornadiene to Quadricyclane

et al. 1999

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In this paper, we report on the bond coupled electron transfer (BCET) isomerization reaction of norbornadiene (NB) to quadricyclane (Q). We have used several triplet sensitizers to examine electron and energy quenching by NB. In the case of acetophenone, energy transfer generates the detectable 3NB, which rearranges to give 3Q which relaxes to Q. Using chloranil, benzoquinone, and 2,5-dichlorobenzoquinone as triplet sensitizers, the triplet ion pairs are generated, but cannot access either 3NB or 3Q, and so the ion pair undergoes return electron transfer to the ground state. However, with 3,3‘,4,4‘-benzophenonetetracarboxylic dianhydride as the triplet sensitizer, the triplet ion pair is generated, but can undergo BCET to 3Q efficiently, which then relaxes to Q. To our knowledge, this is the first example of an efficient electron-transfer mechanism to photoisomerize NB to Q without the intermediacy of 3NB. Consequently, in the valence isomerization of NB to Q, it is possible to directly access the NB-Q triplet surface by controlling the energy of the triplet ion pair photogenerated, and in effect, the quantum yield can be modulated.

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Charge-transfer sensitization of the valence photoisomerization of norbornadiene to quadricyclene by an orthometalated transition-metal complex

Cited by 37 publications

References 2 publications

High Triplet Energy Iridium(III) Isocyanoborato Complex for Photochemical Upconversion, Photoredox and Energy Transfer Catalysis

High Triplet Energy Iridium(III) Isocyanoborato Complex for Photochemical Upconversion, Photoredox and Energy Transfer Catalysis

Bromosubstituted norbornadienes and their reversible photolytic transformation to quadricyclanes

Bond-Coupled Electron Transfer Reactions: Photoisomerization of Norbornadiene to Quadricyclane

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