Solvatochromic Behaviour of Formazans and Contribution of

doi:10.7598/cst2014.836

Chem Sci Trans

2014

DOI: 10.7598/cst2014.836

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Solvatochromic Behaviour of Formazans and Contribution of

Abstract: Abstract:The electronic absorption profiles of 3-cyano-1,5-diarylformazans were recorded in different organic solvents having different polarities. Both macroscopic and microscopic aspects were contemplated to determine the influence of various solute-solvent interactions upon absorption spectral shifts. The effects of solvent polarity on the absorbance profiles of the compounds were evaluated. The multiple linear regression techniques were employed to evaluate Kamlet-Taft coefficients which proved to be instr… Show more

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Cited by 2 publications

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

2021

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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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Solvatochromic Behaviour of Formazans and Contribution of

Cited by 2 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

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