Structures and dynamics of the lowest excited triplet states and cation radicals of phenothiazine and 2-chlorophenothiazine: transient resonance Raman and absorption study

Sarata, Gaku; Noda, Yoichi; Sakai, Makoto; Takahashi, Hiroaki

doi:10.1016/s0022-2860(97)00060-4

Cited by 15 publications

(42 citation statements)

References 18 publications

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“…This spectrum is identical in terms of wavenumbers and relative intensities to the resonance Raman spectrum of pure PTZ + obtained in oxygenated methanol using the 517 nm probe wavelength. 50,51 This finding indicates weak effect of the electrostatic field in the straight channel of zeolite upon the vibrational and electronic properties of PTZ + . It is worth noting that the ring breathing mode at 1030 cm À1 for PTZ + is not observed in off-resonance conditions by using the FT-Raman technique.…”

Section: Resultsmentioning

confidence: 89%

Spontaneous charge separation induced by phenothiazine sorption within acidic HnZSM-5

Moissette¹,

Luchez²,

Brémard³

et al. 2009

Phys. Chem. Chem. Phys.

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In situ diffuse reflectance UV-visible, Raman scattering and EPR experiments, carried out as a function of time after phenothiazine (PTZ) direct exposure to thermally activated acid H(n)ZSM-5 zeolite without any solvent, provide evidence of phenothiazine sorption and simultaneous spontaneous ionization. For comparison, phenothiazine behavior was investigated within non acidic zeolite and showed that most of the phenothiazine molecules were occluded as intact molecules and that ionization was very weak. The multivariate curve resolution analysis of the diffuse reflectance UV-visible spectra set recorded during the sorption process resolve the absorption spectra and respective concentrations of individual species involved in the sorption course. When PTZ entered through the acidic zeolite channels, PTZ (+)@H(n)ZSM-5 (-) radical pair is generated by the polarization energy. Subsequent PTZ(2+) formation was fast but only partial. After months, equilibrium including PTZ (+), PTZ(2+) and occluded PTZ was reached within acid H(n)ZSM-5 but depends on the Si/Al ratio: the higher the Al content, the easier the spontaneous ionization. The close match between PTZ and the pore size of zeolites combined with efficient polarizing effect of proton and aluminium electron trapping sites appear to be the most important factors responsible for the stabilization of PTZ (+) and PTZ(2+) and hinder efficiently the charge recombination. No evidence of Brønsted acid sites of H(n)ZSM-5 was found during the sorption of phenothiazine through generation of protonated species.

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Section: Resultsmentioning

confidence: 89%

Spontaneous charge separation induced by phenothiazine sorption within acidic HnZSM-5

Moissette¹,

Luchez²,

Brémard³

et al. 2009

Phys. Chem. Chem. Phys.

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“…The transient spectrum of Phe showed a maximum at 455 nm with a lifetime of about 1.45 μs assigned to its triplet state, 3 Phe 27. The bimolecular quenching rate constants for the triplet state of Phe by S + and THF were obtained from the decay of the absorption at 455 nm as a function of the quencher concentration, according to where τ and τ 0 are the triplet lifetimes in the absence and in the presence, respectively, of quencher (S + or THF), and [ Q ] is the quencher concentration.…”

Section: Resultsmentioning

confidence: 99%

Cationic photopolymerization of tetrahydrofuran: A mechanistic study on the use of a sulfonium salt-phenothiazine initiation system

Rodrigues

Neumann

2000

J. Polym. Sci. A Polym. Chem.

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The kinetics aspects of the photoinitiated polymerization of tetrahydrofuran with triphenylsulfonium hexafluoroarsenate and sensitized by phenothiazine was studied under visible‐light irradiation. A photosensitizer mechanism was proposed involving electron transfer from phenothiazine to the triphenylsulfonium salt, forming a cation radical, the true precursor of the polymerization. An initial complex in the ground state between the phenothiazine and the triphenylsulfonium was formed prior to the excitation, and this complex actually activated the photopolymerization rate. The polymerization conversion presented an S‐shaped curve, suggesting an induction period caused by the existence of two pathways responsible for the beginning of the polymerization. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 46–55, 2001

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“…The PTZ N+ Raman peaks are identical in terms of position and relative intensity to the resonance Raman spectrum (l ex = 517 nm) of the pure PTZ radical cation in oxygenated methanol. 55,56 In addition, note that the characteristic line expected for PTZ 2+ at about 445 cm 21 is not clearly observed by using the 1064 nm exciting radiation line after two months (Fig. 7, spectrum d).…”

Section: Sorption Of Phenothiazine In H-mormentioning

confidence: 89%

Sorption and spontaneous ionization of phenothiazine within channel type zeolites: Effect of the confinement on the electron transfers.

et al. 2011

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Diffuse reflectance UV-visible absorption and Raman scattering experimental data show evidence of the phenothiazine (PTZ) sorption and spontaneous ionization in the straight channels of three medium pore acid zeolites with various topologies (ferrierite (H-FER), H-ZSM-5 and mordenite (H-MOR)) but analogous Si/Al contents. The spectral data highlight the combined effects of confinement and local electrostatic field on the sorption and charge separation kinetics. The PTZ incorporation and ionization appeared to be quicker in the larger pore H-MOR than in H-ZSM-5 and in H-FER. However, sorption and ionization are almost complete in the three zeolites after about one year. The low ionization potential value of PTZ (I.P. = 6.73 eV) induced quasi instantaneous formation of the radical cation PTZ N+ in high yield within the internal space of each channel structure. Nevertheless, the higher confinement effect and higher polarizing effect offered by the 10-membered rings (10-MR) channels of H-FER favoured the PTZ second ionization to form the dication PTZ 2+ . The very long lifetimes of these charge separated states are probably due to the restricted mobility of PTZ in the narrow channels and to the compartmentalization of the trapped electron away from the initial site of PTZ ionization. However, a very slow charge recombination process is observed within the three zeolite morphologies after about one year. This reaction is only partial in the narrower pores of H-FER and H-ZSM-5 whereas the faster diffusion process within the larger pore H-MOR induces quasi total cation disappearance after 2 years. Therefore, the reaction mechanism indicates clearly that PTZ N+ and PTZ 2+ are only intermediates and that the thermodynamically stable end product is the occluded PTZ molecule.

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Structures and dynamics of the lowest excited triplet states and cation radicals of phenothiazine and 2-chlorophenothiazine: transient resonance Raman and absorption study

Cited by 15 publications

References 18 publications

Spontaneous charge separation induced by phenothiazine sorption within acidic HnZSM-5

Spontaneous charge separation induced by phenothiazine sorption within acidic HnZSM-5

Cationic photopolymerization of tetrahydrofuran: A mechanistic study on the use of a sulfonium salt-phenothiazine initiation system

Sorption and spontaneous ionization of phenothiazine within channel type zeolites: Effect of the confinement on the electron transfers.

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