Coupling Principles in Organic Dyes

Abstract

Dye molecules containing two or more polymethine structural units, or at least one polymethine and one polyene structural unit, generally exhibit coupling effects that determine the spectroscopic behavior and other physicochemical properties of the substance. The coupling concept can be used inter alia to fit the quinone dyestuffs, the indigoids, and the indanthrenes into a general polymethine color system and to predict new dye structures.

Recent Developments in the Colour and Constitution of Organic Dyes

“…For example, the calculated absorption maxima and intensities of the azo compound (34). nitrophenylenediamine (35). methine dye (36), and quinone dye (37) are in reasonable agreement with the experimental values, without making any further adjustments to the parameters listed in Table 1.…”

Molecular mechanisms of the photostability of indigo

“…Semiempirical calculations performed in the 1960s to the 1980s led to the conclusion that the basic chromophore of the indigo dyes is the central C=C bond together with the adjacent C=O and N-H groups. [38][39][40][41][42][43] The excitation energies of singlet excited states of indigo have been extensively studied with ab initio methods 44,45 as well as, more recently, with time-dependent density functional theory (TDDFT) and with inclusion of solvation effects by a polarizable continuum model. [46][47][48][49] However, little attention has been paid to the photochemical reactions of indigo, such as ESIPT and trans → cis photoisomerization.…”

Selective Reduction of Carbonyl Amides: Toward the First Unsymmetrical Bischelating N‐Substituted 1,2‐Diamino‐4,5‐di­amidobenzene

“…[1] The second class of quinonediimines is the largest owing to easy access to symmetrical systems (R 1 = R 2 = R 3 ) and a high stability, which have allowed their use in different fields ranging from hair coloring [12] and biosensors [13] to supramolecular [14] and coordination chemistry. [15] This high stability is explained by the coupling principle [16,17] of the 12π-electron system of the quinoid skeleton, which is best described as being constituted of two 6π-electron subunits chemically connected by two single C-C bonds but each unit is electronically independent (no conjugation). [5] As an extension of these studies, it appeared very attractive to develop the synthesis of new N-substituted p-benzoquinonediimines such as 4, for which a fine tuning of the substituents in the two different, potentially bischelating sites would allow new developments in quinoid and coordination chemistry.…”