Visible absorption spectra of the phenothiazine radical cation and its 10-substituted derivatives

Wagner, Elżbieta; Filipek, Sławomir; Kalinowski, Marek K.

doi:10.1007/bf00810102

Cited by 24 publications

(26 citation statements)

References 9 publications

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“…Advantageously,appearance of such IVCT peak would serve as ad iagnostic peak while characterizing products of photoinduced electron transfer upon excitation of TDPP entity (vide infra). With this in mind, spectroelectrochemical studies were systematically performed for both oxidation and reduction processes.F igure 4s hows the spectral changes observed during the process of first oxidation and first reduction of 1 and 2 in DCB containing 0.2 MT BAPw hile Figure S3 shows such spectral changes for 3 and 5.A ss hown in Figure 4a,d uring first oxidation of 1,asmall increase in the intensity of the original compound was witnessed without the appearance of any new peaks.T his could be attributed to the low molar extinction coefficient values of PTZC +, [18] compared to intense absorptions of TDPP in the monitoring spectral region. In contrast, during first reduction of 1,d ecreased original peak intensity was accompanied by intense new peaks at 1136 nm accompanied by asmaller peak at 1471 nm (Figure 4c), characteristic of IVCT via electron exchange between the two TCBD entities.Inthe case of compounds 2, S3.…”

Section: Methodsmentioning

confidence: 99%

Photoinduced Charge Separation Prompted Intervalence Charge Transfer in a Bis(thienyl)diketopyrrolopyrrole Bridged Donor‐TCBD Push‐Pull System

et al. 2021

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Intervalence charge transfer (IVCT), aphenomenon observed in molecular systems comprised of two redox centers differing in oxidation states by one unit, is reported in anovel, newly synthesized, multi-modular donor-acceptor system comprised of central bis(thienyl)diketopyrrolopyrrole (TDPP) hosting two phenothiazine-tetracyanobutadiene (PTZ-TCBD) entities on the opposite sides.One-electron reduction of TCBD promoted electron exchange between the two TCBD resulting in IVCT transition in the near-infrared region. The stabilization energy, ÀDG com and comproportionation equilibrium constant, K com calculated from peak potentials of the split reduction waves were found to be 1.06 10 4 Jmol À1 ,a nd 72.3 M À1 ,r espectively.F urther,t he IVCT transition was also witnessed during the process of thermodynamically feasible electron transfer upon excitation of the TDPP entity in the system, and served as ad iagnostic marker to characterizet he electron transfer product. Subsequent transient absorption spectral studies and data analysis by Global and Target analyses revealed occurrence of ultrafast charge separation (k cs % 10 10 s À1 )owing to the close proximity and good communication between the entities of the multi-modular donoracceptor system. The role of central TDPP in promoting IVCT is borne out from the present investigation.

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Section: Methodsmentioning

confidence: 99%

Photoinduced Charge Separation Prompted Intervalence Charge Transfer in a Bis(thienyl)diketopyrrolopyrrole Bridged Donor‐TCBD Push‐Pull System

et al. 2021

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“…It is consistent with that observed for PTZ N+ stabilized within H 3.4 ZSM-5 37 and also formed in sulfuric acid or in acetonitrile solution. [48][49][50][51] The last species (d) shows two bands in the visible spectral domain at 437 and between 600 and 700 nm. This spectrum is assigned to the dication PTZ 2+ because of its similarity with the spectrum of this dication produced by photoinduced electron transfer in phenothiazine/semiconductor systems 52 or in sulfuric acid solution.…”

Section: Multivariate Curve Resolution By Alternating Least Squares (...mentioning

confidence: 99%

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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“…5 These compounds are, in general, good electron donors and may be photo-ionized by UVradiation to form the corresponding radical cations that can be characterized by electron paramagnetic resonance (EPR) 6 and UV/Vis spectroscopy. 7 They also readily form charge transfer complexes with various electron acceptors or Lewis acids. 8 Phenothiazines are mostly known as an important class of neuroleptic drugs; however, they exhibit a large variety of pharmacological properties (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…MPS , section 2.3, eqn(7))Solventτ Δ a (μs) Reference sensitizer (R)λ ex P (nm) Φ Δ R λ ex MPS (nm) Φ Δapp MPS Φ Δ MPS k t MPS (M −1 s −1 )a Determined by time-resolved phosphorescence measurements (±2 μs, § 2.3).b Value in good agreement with literature, within experimental error (Φ Δ MPS = 0.19; k t MPS = 8.2 × 10 6 M −1 s −1 ).14a …”

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confidence: 99%

Self sensitized photooxidation of N-methyl phenothiazine: acidity control of the competition between electron and energy transfer mechanisms

Manju¹,

Manoj

Braun

et al. 2012

Photochem Photobiol Sci

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The reaction pathways following electronic excitation of 10-methyl phenothiazine (MPS) in the presence of oxygen have been investigated as a contribution to establish the mechanisms involved in the phototoxic reactions related to phenothiazine drugs. In the context of previously published results, the pathways of oxidation via the radical cation and/or by reactive oxygen species, such as singlet oxygen and superoxide anion, are of particular interest. The effects of polarity of the medium as well as of proton donors on the different reaction pathways, in particular on the formation of reactive oxygen species and the intermediates of the oxidation of 10-methyl phenothiazine, have been investigated. No reaction was observed in non-polar solvents. In polar solvents, both self-sensitized and sensitized singlet oxygen generation lead to the oxidation of MPS and the production of 10-methyl phenothiazine sulfoxide (MPSO) most probably via a zwitterionic persulfoxide. During self-sensitized photooxidation of MPS in the presence of proton donors, such as carboxylic acids, the zwitterionic intermediate is protonated to the corresponding cation that in turn facilitates the reaction with a second molecule of MPS. In the presence of strong acids however, the formation of the radical cation of MPS and of the superoxide anion, by electron transfer from the triplet excited state of MPS to molecular oxygen, competes efficiently with singlet oxygen formation. In this case, the scavenging of the superoxide anion by protons to yield its conjugated acid (hydroperoxyl radical) and the subsequent disproportionation of the latter prevents back electron transfer.

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Visible absorption spectra of the phenothiazine radical cation and its 10-substituted derivatives

Cited by 24 publications

References 9 publications

Photoinduced Charge Separation Prompted Intervalence Charge Transfer in a Bis(thienyl)diketopyrrolopyrrole Bridged Donor‐TCBD Push‐Pull System

Photoinduced Charge Separation Prompted Intervalence Charge Transfer in a Bis(thienyl)diketopyrrolopyrrole Bridged Donor‐TCBD Push‐Pull System

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

Self sensitized photooxidation of N-methyl phenothiazine: acidity control of the competition between electron and energy transfer mechanisms

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