Photochromic properties of 3-methylthio-1,5-diphenylformazan

Grummt, U.‐W.; Langbein, H.; Nöske, Robert; Röbisch, Gerhard

doi:10.1016/0047-2670(84)80006-4

Cited by 6 publications

(4 citation statements)

References 12 publications

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“…As pointed out earlier, this back-relaxation is the subject of our investigations with solvent variation. The addition of other substituents to the formazan may allow a light-induced reaction from yellow I to red I, but for TPF it only proceeds thermally. , In the literature, a debate about the exact isomerization mechanism, especially about the conversion step from the red isomers to the yellow species derived from observed absorption changes and laser flash photolysis studies, can be found. ,,, To verify both the isomerization pathway to the yellow forms and the back-relaxation into red I, we have performed broadband transient absorption (TA) experiments on various time scales. First, we employed a nanosecond laser pulse at 532 nm and monitored the TA for 1 ms after excitation.…”

Section: Resultsmentioning

confidence: 99%

Section: The Journal Of Organic Chemistrymentioning

confidence: 99%

“…Formazans can be present in various forms due to isomerization in both the azo group and the hydrazone group. These properties were investigated quantum-chemically − and with a huge arsenal of experimental techniques, comprising studies on luminescence, , solvatochromism, ,− quantum yield determination, vibrational spectroscopy, ,− electrochemistry, ,, laser flash photolysis, − temperature variation, ,− and the impact of high pressure, in addition to absorption measurements, to name a few.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity of Isomerization Kinetics of 1,3,5-Triphenylformazan on Cosolvents Added to Toluene

2021

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Formazan molecules exhibit photochromism because isomerization processes following excitation may occur in both the azo group and the hydrazone group; thus, each formazan may be present in various forms with different colors. The ratio of these forms depends on the illumination conditions and the environment of the formazan with a most incisive sensibility of the thermal anti-syn relaxation of the CN toward slight traces of impurities in toluene solutions, as reported most prominently for 1,3,5-triphenylformazan. Here, we study the latter compound with transient absorption spectroscopy to investigate the role of these traces by adding small amounts of both protic and aprotic cosolvents. Whereas the activation barrier decreases if the binary solvent mixture has a higher polarity, the role of hydrogen bonding can have a reverse impact on the thermal isomerization rate. Both the addition of an aprotic cosolvent and the addition of a protic cosolvent can slow the reaction due to their hydrogen-bond accepting and hydrogen-bond donating properties, respectively. In the case of methanol as a cosolvent, this effect outweighed that of the polarity increase for small concentrations, which was not observed for the fluorinated alcohol hexafluoroisopropanol. The results are explained in the context of a competition between solute−cosolvent and cosolvent−cosolvent hydrogen bonding.

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Section: Resultsmentioning

confidence: 99%

Section: The Journal Of Organic Chemistrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sensitivity of Isomerization Kinetics of 1,3,5-Triphenylformazan on Cosolvents Added to Toluene

2021

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“…So how is it possible that a thermal process leads from ZEZE (red II) to EZEE (yellow I) without any detectable intermediates? In chelated formazan isomers exhibiting an intramolecular hydrogen bond, intramolecular proton transfer was reported to occur in the ground state ( Fischer et al, 1968 ; Hutton and Irving, 1980 ; Hutton and Irving, 1982 ; Grummt et al, 1984 ), and also IR spectra in solution and in the solid state point towards this pathway ( Otting and Neugebauer, 1968 ; Otting and Neugebauer, 1969 ). A combined IR and resonance Raman study, also of unsymmetrical derivates of TPF, found evidence for this tautomerism even in the photochemical generation of non-chelated isomers and interpreted the transfer step to occur in the excited state ( Lewis and Sandorfy, 1983 ).…”

Section: Analysis Of Reaction Pathwaysmentioning

confidence: 99%

Monitoring the photochemistry of a formazan over 15 orders of magnitude in time

Wortmann

Kutta²,

Nuernberger³

2022

Front. Chem.

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2,3,5-triphenyltetrazolium chloride (TTC) may convert into phenyl-benzo[c]tetrazolocinnolium chloride (PTC) and 1,3,5-triphenylformazan (TPF) under irradiation with light. The latter reaction, albeit enzymatically rather than photochemically, is used in so-called TTC assays indicating cellular respiration and cell growth. In this paper, we address the photochemistry of TPF with time-resolved spectroscopy on various time scales. TPF is stabilized by an intramolecular hydrogen bond and switches photochemically via an E-Z isomerization around an N=N double bond into another TPF-stereoisomer, from which further isomerizations around the C=N double bond of the phenylhydrazone group are possible. We investigate the underlying processes by time-resolved spectroscopy in dependence on excitation wavelength and solvent environment, resolving several intermediates over a temporal range spanning 15 orders of magnitude (hundreds of femtoseconds to hundreds of seconds) along the reaction path. In a quantum-chemical analysis, we identify 16 stable ground-state isomers and discuss which ones are identified in the experimental data. We derive a detailed scheme how these species are thermally and photochemically interconnected and conclude that proton transfer processes are involved.

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Resonance Raman studies of the structures and vibrational assignments of photochromic S‐alkyldithizones

Takahashi

Yamada

Isaka

et al. 1988

J Raman Spectroscopy

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The resonance Raman spectra of S-rnethyldithizone (MeHDz), S-ethyldithizone (EtHDz) and S-isopropyldithizone (iPrHDz) have been measured in the solid state and in solution. It is shown that the red and yellow isomers of these S-alkyldithizones adopt in solution the trans-syn-s-trans and trans-unti-s-trans configurations, respectively, with respect to the N=N, C-N and C-N bonds of the formazan skeleton. It is also demonstrated that for EtHDz the red and yellow isomers can be isolated as different crystal forms. Vibrational assignments are given for both red and yellow isomers of MeHDz based on the frequency shifts of five kinds of isotopically substituted species. INI'RODUCTION S-Alkyldithizones (3-alkylthio-1,5-diphenylformazans)are known to exhibit colour changes in solution.'*2 The colour of a freshly prepared solution of Smethyldithizone (MeHDz) is permanganate pink. On keeping the solution in the dark or in diffused light at room temperature, the colour slowly changes to yellowbrown with a concomitant spectral change; the absorption peak originally at 545 nm decreases in intensity as a new peak appears at 415 nm (Fig. 1A). This process is greatly accelerated on illumination with green light, but is reversed with light of shorter wavelength.S-Isopropyldithizone (iPrHDz) also exhibits a colour change in solution. However, the change is opposite : the lcolour of a fresh solution is yellow ( A, , , = 410 nm), and it gradually turns brownish on standing with a new absorption maximum at 550 nm (Fig. 1B).Although it is generally accepted that these colour changes of S-alkyldithizones are due to thermal and r---1

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Photochromic properties of 3-methylthio-1,5-diphenylformazan

Cited by 6 publications

References 12 publications

Sensitivity of Isomerization Kinetics of 1,3,5-Triphenylformazan on Cosolvents Added to Toluene

Sensitivity of Isomerization Kinetics of 1,3,5-Triphenylformazan on Cosolvents Added to Toluene

Monitoring the photochemistry of a formazan over 15 orders of magnitude in time

Resonance Raman studies of the structures and vibrational assignments of photochromic S‐alkyldithizones

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