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Bitterfeld-Wolfen, Germany

The quantum mechanical model is fully recognized and used for rotational and vibronic transitions in molecules, where according to the model, transitions occur between discrete, the resonance condition matching states, only. It is also accepted that selection rules are implied for rotational and vibronic transitions. Why is it so hard to recognize that this established quantum mechanical model is also valid for vibronic transitions, where the Franck-Condon principle instead of a selection rule applies to the population of vibronic states in the electronic excitation state? In any case, supposed illustrative and comfortable but wrong explanations, also if they are widely used, must not replace more sophisticated, correct quantum mechanical models. In scientific publications as well as in teaching only the quantum mechanical version of the Franck-Condon principle should be used. Terms like "Franck-Condon point" or "Franck-Condon region of the photochemical reaction" should be avoided in the future. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Schmitz C.,Niederrhein University of Applied Sciences | Halbhuber A.,Niederrhein University of Applied Sciences | Keil D.,FEW Chemicals GmbH | Strehmel B.,Niederrhein University of Applied Sciences
Progress in Organic Coatings | Year: 2016

Photoinitiated radical polymerization using as photoinitiator system a combination of NIR-sensitizer (Sens) and a radical initiator (RI) was investigated in different multifunctional monomers derived from the multifunctional acrylic esters HDDA, TPGDA, PEGDA, and TMPTA. NIR-LEDs were applied for exposure exhibiting their emission maximum either at 750nm, 790nm, 830nm or 940nm. Solubility of Sens in the respective monomers, their absorption data (λabs max, εmax), fluorescence data (Φf, λf max), electrochemical data (E ox, E red) and the free energy of electron transfer (δG el) between the excited state of Sens and RI were compiled. It showed for many systems an exothermic behavior, which does not always correlate with reactivity. Iodonium salts with low coordinating anions ([B(Ph)4]-, [B(Ph-F5)4]-, [(CF3SO2)2N]-, PF6 -) and Triazine A (2,4-Bis(trichloromethyl)-6-(4-methoxy)phenyl-1,3,5-triazine) were applied as RI. Sens was selected from the group of cyanines in which neutral compounds exhibited the highest reactivity. Cationic sensitizers showed almost no initiating reactivity. Furthermore, the sensitizer (5-(6-(2-(3-Ethyl-1,1-dimethyl-1H-benzo[e]indol-2(3H)-ylidene)ethylidene)-2-(2-(3-ethyl-1,1-dimethyl-1H-benzo[e]indol-3-ium-2-yl)vinyl)cyclohex-1-en-1-yl)-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate) (S9) was taken to study the effect of wavelength dependent LED excitation. The highest reactivity was found for the LED emitting at 850nm where the system possesses the highest excitation volume and the lowest absorption of photoproducts. Furthermore, thermal investigation approved that the combination S9 and iodonium salt can be considered as a thermal initiation system either. Thus, these systems can be seen as hybrid initiator systems. Finally, we show for the first time the generation of solvated protons using different iodonium salts and sensitizers in acetone as surrounding. The activity of solvated protons was evaluated showing a certain reactivity tendency. The number of solvated protons with respected to the number of sensitizer molecules was lower than unity showing their consumption by nucleophilic centers. © 2016 Elsevier B.V.

Mustroph H.,FEW Chemicals GmbH | Ernst S.,FEW Chemicals GmbH | Senns B.,FEW Chemicals GmbH | Towns A.D.,Vivimed Labs Europe Ltd
Coloration Technology | Year: 2015

The creation of the first synthetic dyes not only stimulated the hunt for new colorants but also drove the search for rules correlating the constitution of organic compounds with their colour. Dye chemistry additionally facilitated the development of molecular electronic spectroscopy as well as theories of molecular electronic structure and electronic transitions. Powerful quantum chemical computational tools are now available for the prediction of the electronic structure and spectroscopic characteristics of organic compounds. Such methods are thus useful in designing new functional colorants and aiding interpretation of their properties. However, without a deep appreciation of the principles and assumptions behind the calculations, one runs the risk of misunderstanding what can be achieved as well as becoming confused about how the outputted electronic and vibronic transition data correspond to observed absorption spectra. This review therefore aims to cover fundamentals of electronic spectroscopy that are often overlooked and enable the dye chemist using modern computational methods to comprehend the subtle differences in the types of transition energy value that such software can generate. In addition, the limitations of these methods in predicting absorption maxima and intensities of real-world colorants will be discussed in the context of physical influences on absorption band position and shape, for example from the perspective of different forms of the Franck-Condon principle. In essence, the goal of this review is to clarify, in terms that practical dye chemists will understand, what computational methods can predict and how valid these predictions are compared with reality. © 2015 Society of Dyers and Colourists.

Strehmel B.,Niederrhein University of Applied Sciences | Ernst S.,FEW Chemicals GmbH | Reiner K.,FEW Chemicals GmbH | Keil D.,FEW Chemicals GmbH | And 2 more authors.
Zeitschrift fur Physikalische Chemie | Year: 2014

This contribution discusses photoinitiated crosslinking of multifunctional acrylic esters in polymeric binders based on digital imaging using the Computer to Plate (CtP) technology applying laser exposure at 830 nm in the near infrared (NIR). All coating components (NIR photoinitiator system, monomers, binder, adhesion promoter, contrast dye, and oxygen barrier material) were applied as thin double layer film (1-2 μmdry film thickness) on Al-plateswith an anodized surface. Materials exposed exhibit a sensitivity between 30-200 mJ/cm2depending on the NIR-photoinitiator composition. This was processed in a weak aqueous alkaline bath to obtain the image. Generation of initiating radicals occurs by electron transfer from the excited state of the NIR-sensitizer to the radical generator; that is either an oniumsalt or neutral electron deficient compound. Redox potentials were determined for the NIR-sensitizers and the radical generator. These data allow a rough estimate regarding the free energy of electron transfer of the excited state of the sensitizer and radical generator in NIR-photosensitive imaging material. Photoinduced electron transfer plays a major function to generate initiating radicals by a sensitized mechanism but thermal events also influence sensitivity of the coating. Particular the non-radiative deactivation of the NIR-sensitizer possesses a major function to release selectively the heat. Absorption data of manyNIR-sensitizers used exhibitmolar extinction coefficient ofmore than 200 000M-1cm-1.

Mistol J.,FEW Chemicals GmbH | Ernst S.,FEW Chemicals GmbH | Keil D.,FEW Chemicals GmbH | Hennig L.,University of Leipzig
Dyes and Pigments | Year: 2015

Squaraines containing 2,3-dihydro-1H-perimidine terminal groups have been known since 1993. In the literature two structure types have been described; those involving bonding of the four-membered ring to C-4 and those involving bonding to C-6 of the dihydroperimidine unit. It was found by extensive application of one dimensional and two-dimensional nuclear magnetic resonance spectroscopic techniques, that the 2,3-dihydro-1H-perimidine terminal groups are linked at their 4-position with the four-membered cyclic ring, and not at their 6-position. It was also found by nuclear magnetic resonance spectroscopy that hindered rotation about the partial double bond between the 2,3-dihydro-1H-perimidine terminal groups and the central four membered cyclic ring, leads to a syn-anti isomerization of the dihydroperimidine derived squaraine dyes. This feature is confirmed by the detection of two isomers using 2nd order derivative ultraviolet-visible absorption spectroscopy. © 2015 Elsevier Ltd. All rights reserved.

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