Untersuchungen zum UV/VIS‐Spektralverhalten von Azofarbstoffen. IIIEmpirische, an Azobenzenen gewonnene Absorptionsinkremente und ihre Beziehungen zu Reaktivitätskonstanten, spektroskopischen Substituentenkonstanten und Ionisierungspotentialen

Abstract

Studies on UV/VIS Absorption Spectra of Azo Dyes. III. Empirical Absorption Increments Derived from Azobenzenes and their Relationship to Reactivity Constants, Spectroscopic Substituent Constants and Ionisation Potentials Absorption increments ϵ which specifically characterize the substituents are derived from the difference in exitation energy between azobenzene and monosubstituted azobenzenes. These increments have been found to predict accurately the effect of substituents of the long wave π → π* band of polysubstituted azobenzenes. Comparison of the ϵ values with HAMMETT‐σ reactivity constants reveals direct proportionality between the two sets of constants. There is also a direct proportionality between the increments and spectroscopic substituent constants introduced by BLOOR and COPLEY. Furthermore, a correlation of the ϵ values with the ionization potentials of substituents was found.

Quantum Chemical Investigation of Thermal Cis-to-Trans Isomerization of Azobenzene Derivatives: Substituent Effects, Solvent Effects, and Comparison to Experimental Data

“…The last column gives Hammett substituent constants σ, taken from ref . Some of the σ values of ref are different from the original Hammett values and have been especially adapted for azobenzenes.…”

“…Here, k H is the cis f trans isomerization rate constant of azobenzene and k X is that of the X-substituted species. σ is the substituent constant, whose values are also tabulated in Table 2 and taken from ref 39. In the Hammett plot, which is shown in Figure 7, substituents with positive σ (3-CN, 4-CN, and 4-NO 2 ) accelerate the reaction, but also substituents with negative σ (4-OMe, 5-NH 2 , and 4-NH 2 ) do.…”

Cobalt Antiferromagnetic Ring and Grid Single‐Molecule Magnet

“…Recently, Taherpour and Shafiei5 studied the structural relationship between Randić indices, the determinants of the adjacency matrixes and distance matrixes to maximum wavelength of linear simple conjugated polyene compounds H 2 CCH(HCCH) n H ( n = 1, 2, 3,…, 24). For substituted aromatic derivatives, now, there are three main kinds of parameters applied to study the substituent effect on UV spectra: (1) Polar substituent parameter,6 such as Hammett constant σ p ; some workers7–11 used two straight lines or the absolute values of polar substituent constant, | σ p | for a ‘successful’ correlation of UV data. (2) Free radical substituent parameter,12–14 for example spin‐delocalization substituent constant ${\rm \sigma }_{{\rm JJ}}^ \bullet $ ; Jiang et al 15, 16.…”

Determining the excited‐state substituent constants of meta‐substituent from 3,4'‐disubstituted stilbenes

“…Researches showed that the UV absorption energy of compounds can be affected by the type and position of substituents in a narrow range, and knowledge of the correlation between molecular structure and UV absorption energy is helpful to design optical molecules . Therefore, considerable effort has been devoted to the correlation between substituent effect and UV absorption energy . In early researches, the substituent effect on UV energy of compounds was scaled with the polar constant, for example, Hammett constant σ p .…”

“…Therefore, considerable effort has been devoted to the correlation between substituent effect and UV absorption energy . In early researches, the substituent effect on UV energy of compounds was scaled with the polar constant, for example, Hammett constant σ p . In 1995, Jiang X. K. et al .…”