Methylene Blue Encapsulation in Cucurbit[7]uril: Laser Flash Photolysis and Near-IR Luminescence Studies of the Interaction with Oxygen
| Autor: | J. C. Scaiano, Pedro Montes-Navajas, María González-Béjar, Hermenegildo García |
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| Rok vydání: | 2009 |
| Předmět: |
Macrocyclic Compounds
Spectrophotometry Infrared Nitrogen chemistry.chemical_element Quantum yield Electrons Photochemistry Oxygen chemistry.chemical_compound Electrochemistry General Materials Science Triplet state Coloring Agents Spectroscopy Photolysis Photosensitizing Agents Singlet Oxygen Singlet oxygen Air Lasers Surfaces and Interfaces Condensed Matter Physics Methylene Blue Solutions Kinetics chemistry Excited state Luminescent Measurements Flash photolysis Luminescence Oxidation-Reduction Methylene blue |
| Zdroj: | Langmuir. 25:10490-10494 |
| ISSN: | 1520-5827 0743-7463 |
| DOI: | 10.1021/la9011923 |
| Popis: | The effect of methylene blue (MB) encapsulation in cucurbit[7]uril (CB[7]) on triplet excited-state behavior and singlet oxygen (1O2) generation has been studied by using laser flash photolysis (LFP) and time-resolved near-IR luminescence spectroscopy. The lifetime of the triplet excited state of MB is longer in the CB[7] cavity (140 micros for MB-CB[7] vs 79.5 micros for aqueous MB). Cucurbituril also protects the dye triplets from quenching by oxygen, reducing the quenching rate constant [kq(O2)] from 2.6x10(9) M(-1) s(-1) to 0.2x10(9) M(-1) s(-1). The quantum yield of 1O2 production in the air-equilibrated D2O solutions is similar for free MB and for MB-CB[7], and the singlet oxygen lifetime is approximately 70 micros, suggesting its decay occurs in the aqueous (D2O) phase. The generation of singlet oxygen is delayed by CB[7]; this is attributed to the time required for oxygen to access the CB[7] nanocavity and react with the MB triplet. Thus, the rate-limiting step for sensitization is the entry of oxygen into the CB[7] cavity. Encapsulation inside CB[7] increases the relative efficiency of photoinduced MB2+* dication-radical generation, for which a modest yield is observed. |
| Databáze: | OpenAIRE |
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