Gigantic Magnetic Field Effect on the Long-Lived Intermolecular Charge-Separated State Created at the Nonionic Bilayer Membrane

Abstract

For realization of low-cost organic photon-energy conversion, the supramolecular approach has been a focus of attention as a counter approach to precise synthesis of covalently linked donor (D)–acceptor (A) molecules. Here we report photogeneration of a long-lived (∼3 μs) intermolecular charge-separated (CS) state of metal porphyrins (D) and an alkyl viologen (A) at an interface of a vesicle membrane formed by self-assembly of nonionic surfactant and cholesterol molecules. The yield of escaped free radicals is negligibly low as in the case of CS states in covalently linked D–A systems. Furthermore, the transient concentration of the CS state dramatically increases by ∼100% upon application of a magnetic field of 250 mT at room temperature. The simulation of the spin dynamics of the CS state indicates that fast (∼107 s–1) spin-selective recombination and slow (105–106 s–1) dissociation–re-encounter dynamics are the key processes for the long CS-state lifetime and the gigantic magnetic field effect. It has turned out that such dynamics are sharply dependent on temperature and alkyl chain length of the viologen. The present results would lead to the development of future materials for light energy conversion, drug delivery, and microscopic bioprobes.

Photogenerated Radical Pair between Flavin and a Tryptophan-Containing Transmembrane-Type Peptide in a Large Unilamellar Vesicle

“…This feature is in sharp contrast with the previously reported niosome (PEG-based vesicle) system, where microsecondorder longitudinal diffusion of the embedded molecules plays an important role on a gigantic MFE (∼100%) and a long radical pair lifetime (∼a few μs). 48 Thus, the rigidity of the peptide and the hydrophobic region of the liposome is presumably higher than that of the hydrated PEG region of the niosome.…”

Photoreaction of 9,10-Anthraquinone-2,6-disulfonic Acid and Ascorbic Acid Complexed at the Cationic Bilayer Interface and Consecutive Radical Dynamics

“…This means that T 1 of AQDSH •2– is extremely longer than that of Asc •– because the long rotational correlation time of the vesicle controls the T 1 as represented in eq . The long T 1 is known to be observable in the low-temperature solution and also in confined environments, where τ c is long. , This indicates that two kinds of radicals interact with the bilayer interface differently, namely, there is no possibility that these radicals exist as a complexed radical pair after the photoreaction. This is consistent with no observation of SCRP.…”

Effects of the Peripheral Substituents, Central Metal, and Solvent on the Photochemical and Photophysical Properties of 5,15‐Diazaporphyrins

“…Nanosecond transient absorption spectroscopy was carried out with setup described elsewhere . Briefly, the second harmonics from a Nd : YAG laser (Continuum Minilite, duration of 10 ns, repetition of 10 Hz) and white continuous light from a 75 W xenon lamp (OBB Power Arc) were used as pump and probe light sources, respectively.…”

“…Nanosecond transient absorption spectroscopy was carried out with setup described elsewhere. [18] Briefly, the second harmonics from a Nd : YAG laser (Continuum Minilite, duration of 10 ns, repetition of 10 Hz) and white continuous light from a 75 W xenon lamp (OBB Power Arc) were used as pump and probe light sources, respectively. The probe light passing through the sample solution in a 1 cm quartz cuvette was dispersed with a monochromator (Spectral Products CM110) and detected with a photomultiplier tube (Hamamatsu R955).…”