High intensity laser photochemistry of organic molecules in solution

Wilson, R. Marshall; Schnapp, K. A.

doi:10.1021/cr00017a011

Cited by 50 publications

(39 citation statements)

References 53 publications

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“…Multiphoton excitation of organic molecules offers many applications and is a growing field in laser chemistry. In most cases, high-intensity UV-laser excitation of organic molecules produces radicals that further react to form stable photoproducts (1)(2)(3), and in aqueous solutions solvated electrons are formed (43).…”

Section: Introductionmentioning

confidence: 99%

One‐ and Two‐Photon‐Induced Photochemistry of Modified Palladium Porphyrazines Involving Molecular Oxygen

Freyer¹,

Stiel

Hild

et al. 1997

Photochem & Photobiology

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Abstract— Octaphenyltetraanthraporphyrazinato palladium undergoes a self‐sensitized photoreaction in the presence of oxygen to form a substituted palladium phthalocyanine with four endoperoxide bridges. This compound exhibits photophysical behavior similiar to palladium tetra‐tert‐butyl‐phthalocyanine. The phthalocyanine‐palladium complex with four endoperoxide bridges ejects molecular oxygen when excited by consecutive two‐photon absorption in the Q‐band region at 662 nm. This photocyclo‐reversion, which produces palladium porphyrazines bearing a diminished number of endoperoxide bridges, can occur up to four times per initial molecule. Irradiation of these photoproducts in the presence of oxygen produces substituted palladium phthalocyanine containing four endoperoxide groups.

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Section: Introductionmentioning

confidence: 99%

One‐ and Two‐Photon‐Induced Photochemistry of Modified Palladium Porphyrazines Involving Molecular Oxygen

Freyer¹,

Stiel

Hild

et al. 1997

Photochem & Photobiology

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“…In photochemistry the situation is much more complex, as fates of excited states are governed by competing pathways for reaction, coupling to other electronic states, possible further photoexcitation, and relaxation to the ground state; thus, the outcomes of such processes are difficult to control once initiated. Some useful selectivity through singlet or triplet states can be achieved by a number of means, including use of triplet quenchers or sensitizers,1–3 irradiation at user‐selected wavelengths,4 through higher exited states from multiphoton absorption,5, 6 and feedback‐based optical control using evolutionary algorithms and pulse shapers 7…”

Section: Methodsmentioning

confidence: 99%

Product Selection through Photon Flux: Laser‐Specific Lactone Synthesis

et al. 2008

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In ground-state chemistry, such as metal-catalyzed processes, exquisite levels of reaction control can often be achieved by subtle changes to the catalyst or reaction conditions. In photochemistry the situation is much more complex, as fates of excited states are governed by competing pathways for reaction, coupling to other electronic states, possible further photoexcitation, and relaxation to the ground state; thus, the outcomes of such processes are difficult to control once initiated. Some useful selectivity through singlet or triplet states can be achieved by a number of means, including use of triplet quenchers or sensitizers, [1][2][3] irradiation at user-selected wavelengths, [4] through higher exited states from multiphoton absorption, [5, 6] and feedback-based optical control using evolutionary algorithms and pulse shapers. [7] Herein, we describe how photon flux [8] can be used to switch cleanly between Norrish type I and type II pathways [1, 5, 6f-l,9] in the photochemical rearrangement of 1,3-indandiones.[10] In particular, the study demonstrates that photon flux, not average power or wavelength, is the controlling factor in product selection.As part of an ongoing study of the [5+2] photocycloaddition of maleimides, [11,12] we investigated the photochemistry of 2-ethyl-1,3-indandione 1 (Scheme 1). Unfocused [13] Nd:YAG laser irradiation of 1 at 266 nm [14] gave rise to the volatile g-alkylidinephthalide lactones 2 as an E/Z mixture (18 %). Using the higher power output of the laser at 355 nm (350 mW), a yield of 60 % of isolated 2 was obtained after 18 h. Addition of isoprene as a triplet quencher had no effect, suggesting a singlet mechanism. Quantum-yield (F) measurements using tunable lasers at five specific wavelengths between 222 and 355 nm indicated an inefficient photochemical reaction (F = 0.5-3.3 %).At this point we attempted to scale up the formation of 2 by irradiating 1 with higher (average) power UV lamps. To our surprise, however, irradiation of 1 with a low-pressure phosphor-coated mercury lamp (312 nm) gave only the diones 3 and 4 (43 %, 2:1). Similar results were obtained using medium-pressure lamps (125-600 W). Irradiation of 1 in CD 3 CN and direct analysis of the photosylate by 1 H NMR spectroscopy showed greater than 99 % of 3 and 4 and a trace of 2 (less than 1 %). These results indicate that the pathway leading to 2 is effectively closed for lamp irradiation. Significantly, addition of isoprene (one equivalent) resulted in quenching of the reaction and recovery of 1, thus indicating that 3 and 4 are formed from a different (triplet) pathway on lamp irradiation.This stark, source-dependent difference in behavior can be explained by the mechanisms in Scheme 2. Initial excitation of 1 with either source leads to the singlet state (S 1 ), from which two separate pathways can evolve. With the laser, S 1 undergoes a cleavage to the diradical 5 and subsequent recombination to the lactones 2 through a Norrish type I pathway. A singlet manifold is supported by the lack of quenchin...

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“…Another widely used physical stimulus is light, which leverages hydrogelators encoded with light‐sensitive groups (e.g., photocleavable groups, photoisomerizable groups) to trigger phase transitions . One key advantage of light as a trigger is the potential use of coherent light sources such as laser, which allows creation of supramolecular hydrogels with high spatial resolution . Polypeptides or small molecules encoded with light‐sensitive moieties such as 2‐nitrobenzyl groups have been shown to form supramolecular structures when exposed to light of wavelength 260 < λ < 365 nm .…”

Section: Physical Stimuli‐responsive Hydrogelsmentioning

confidence: 99%

Stimuli‐Responsive Supramolecular Hydrogels and Their Applications in Regenerative Medicine

Hoque

Sangaj

Varghese

2018

Macromolecular Bioscience

145

108

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Supramolecular hydrogels are a class of self-assembled network structures formed via non-covalent interactions of the hydrogelators. These hydrogels capable of responding to external stimuli are considered to be smart materials due to their ability to undergo sol–gel and/or gel–sol transition upon subtle changes in their surroundings. Such stimuli-responsive hydrogels are intriguing biomaterials with applications in tissue engineering, delivery of cells and drugs, modulating tissue environment to promote innate tissue repair, and imaging for medical diagnostics among others. This review summarizes the recent developments in stimuli-responsive supramolecular hydrogels and their potential applications in regenerative medicine. Specifically, various structural aspects of supramolecular hydrogelators involved in self-assembly, the role of external stimuli in tuning/controlling their phase transitions, and how these functions could be harnessed to advance applications in regenerative medicine are focused on. Finally, the key challenges and future prospects for these versatile materials are briefly described.

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High intensity laser photochemistry of organic molecules in solution

Cited by 50 publications

References 53 publications

One‐ and Two‐Photon‐Induced Photochemistry of Modified Palladium Porphyrazines Involving Molecular Oxygen

One‐ and Two‐Photon‐Induced Photochemistry of Modified Palladium Porphyrazines Involving Molecular Oxygen

Product Selection through Photon Flux: Laser‐Specific Lactone Synthesis

Stimuli‐Responsive Supramolecular Hydrogels and Their Applications in Regenerative Medicine

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