Long-Lived Charge-Separation by Retarding Reverse Flow of Charge-Balancing Cation and Zeolite-Encapsulated Ru(bpy)₃²⁺as Photosensitized Electron Pump from Zeolite Framework to Externally Placed Viologen

Abstract

K(+)-exchanged, Ru(bpy)(3)(2+)-encapsulating zeolite-Y [K(+)-Ru(bpy)(3)(2+)Y] and N-[3-(dicyclohexylmethyl)oxypropyl-N'-methyl-4,4'-bipyridinium [DCH-MV(2+)] were prepared, and visible light-induced electron transfer from the zeolite-encapsulated Ru(II) complex to the size-excluded viologen was studied in acetonitrile. Addition of a series of crown ethers (CEs) into the heterogeneous solution leads to over a 10-fold increase in the yield of DCH-MV(*)(+), where the yield linearly increases as the formation constant of CE with K(+) [K(f)(K(+))(CE)] increases. The following two sequential events are attributed to be responsible for the above novel phenomenon. First, K(+) ions are liberated from the zeolite to solution during interfacial electron transfer from the photoexcited Ru(II) complexes to DCH-MV(2+). Second, the liberated K(+) ions form strong host-guest complexes with the added CE molecules, which leads to retardation of the reverse flow of the cations, hence the charge-balancing electrons, from the solution to the zeolite. Surprisingly, the yield of DCH-MV(*)(+) reaches more than approximately 50 times the amount of Ru(bpy)(3)(2+) situated in the outermost supercages, despite the absence of electron relay in the zeolite. This is attributed to photosensitized electron pumping from the zeolite framework to viologen by the outermost Ru(bpy)(3)(2+) ions. In support of the above conclusion, Ru(bpy)(3)(3+) does not accumulate in the zeolite host while DCH-MV(*)(+) accumulates in the supernatant solution. Consistent with the above, the independently prepared hexafluorophosphate salt of Ru(bpy)(3)(3+) is reduced to Ru(bpy)(3)(2+) in acetonitrile upon contact with Ru(bpy)(3)(2+)-free M(+)Y (M(+) = Li(+), Na(+), K(+), Rb(+), and Cs(+)), where the yield increases as the donor strength of the framework oxygen increases. Although small, thermal electron transfer also takes place from the zeolite framework to DCH-MV(2+), where the yield increases upon increasing the donor strength of the framework, concentration of DCH-MV(2+), temperature, and K(f)(K(+))(CE) (when K(+)Y is the zeolite host). The photoyield is always higher than the thermal yield by 4-30 times, confirming that the zeolite-encapsulated Ru(bpy)(3)(2+) serves as the photosensitized electron pump.

Zeolite matrix assisted decomposition of singlet oxygen sensitizers during photooxidation

“…[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] It has also been shown that the zeolite surface can serve as an electron donor. [53,54] Further it has been established that CsY is a better electron donor than NaY. [20,[49][50][51][52][53][54] The observation of the dye being less stable within CsY than in NaY is consistent with these established facts.…”

Redox‐Induced Molecular Metamorphism Promoting a Sol/Gel Phase Transition in a Viologen‐Based Coordination Polymer

“…Consistent with the literature, we found that viologen cation radicals can be photogenerated in situ, either by directi rradiation of the viologen moieties (300 < l < 400 nm) [50][51][52][53][54][55] or by excitation of as uitable photosensitizer such as tris(bipyridine)ruthenium(II) chloride (RuBPy; l ex % 450 nm) introduced in catalytic amount. [56][57][58][59] In our experimental conditions (thin-layer cell,i n situ measurements, concentrated sample),p hoto-production was found to be most effectiveu sing al ed lamp X-Cite 120LEDBoost equipped with al ong-pass filter (l > 360 nm) enabling to excite the viologen moieties. Particle tracking microrheology measurements [60] have been performed prior and after irradiation for Dt (irradiation time) of the thin layer cell mounted on the microscope.S uch micrometric analyses involvedt akinga dvantage of the dynamics of the colloidsa ctivated by thermale nergy k B T,w ith k B the Boltzmann constant and T = 20 8Ct he temperature of the sample, to probe the viscoelastic properties of the sample.…”

Syntheses of Precursors and Reference Compounds of the Melanin-Concentrating Hormone Receptor 1 (MCHR1) Tracers [11C]SNAP-7941 and [18F]FE@SNAP for Positron Emission Tomography

“…The hydroxypropyl analogue 36 was synthesized in a one-pot two-step reaction as shown above in Scheme 8 adapting the methods of Heidecke/Lindhorst and Park et al [25,26]. The cleavage to hydroxypropyl ester 36 was accomplished in an anti-Markovnikov reaction using a borane-tetrahydrofuran complex and hydrogen peroxide.…”

“…After purification of the raw product (5.23 g, brown oil) via column chromatography (silica gel, eluent: CH 2 Cl 2 /MeOH 9.5:0.5), the bromide 24 could be obtained as a yellow oil (1.41 g, 58.2%). (26). To a solution of 2-(t-butyldiphenylsilyloxy)ethyl 4-(3,4-difluorophenyl)-6-(methoxymethyl)-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate (19, 1.10 g, 1.89 mmol) and 4-nitrophenylchloroformate (1.34 g, 6.65 mmol) in THF (24.0 mL), LiHMDS (5.3 mL, 892 mg, 5.33 mmol, 1 M in THF) was added dropwise at −78 °C.…”