Cyanines aromaticity

There are several other classes of polymers being examined for high-temperature adhesive and composite applications, such as phthalo-cyanines, " aromatic nitriles,polytriazines, ladder polymers such as poly-bis(benzimidazophenanthroline) (BBP polymers), " and polyphenylene." Many of these materials are not commercially available and much more work is needed before successful applications will be found. 

Condensed aromatic compounds (benzoselenazoles) are considered much more stable, and they are in fact more commonly used in the area of cyanine-type photographic dyes. 

Cyanine dyes containing one or two phosphate groups attached directly to the aromatic indolenine residues were recently reported by M. Reddington [26],... 

The indole- and benzindole-cyanine dyes illustrated in Scheme 6 are used by many major manufacturers in optical disk recording applications. These types of dye tend to be more light-stable than many other readily synthesized polymethine dyes. To increase the photostability, the dyes are used in combination with various types of stabilizers such as nickel dithiolato complexes and selected tertiary aromatic amine compounds.199 The application of cyanine dyes for optical storage media was primarily developed in Japan203 and several dyes and compatible stabilizers are commercially available in pure form from Japanese suppliers.199... 

Of some importance as textile dyes are aza analogues of polymethine (cyanine) dyes. Azacarbocyanines result when Fischer s aldehyde is heated with primary aromatic amines. Thus Cl Basic Yellow 11 (6.220) is obtained when Fischer s aldehyde is condensed with 2,4-dimethoxyaniline. The equivalent reaction with 2-methylindoline gives Cl Basic Yellow 21 (6.221), which has superior light fastness but has been classified by ETAD as toxic [73]. The tinctorially strong golden yellow diazacarbocyanine dye Cl Basic Yellow 28 (6.222) is prepared by coupling diazotised p-anisidine with Fischer s base (6.223), followed by quaternisation with dimethyl sulphate. Some triazacarbocyanine dyes are also used commercially. 

All polycyclic pigments, with the exception of triphenylmethyl derivatives, comprise anellated aromatic and/or heteroaromatic moieties. In commercial pigments, these may range from systems such as diketopyrrolo-pyrrol derivatives, which feature two five-membered heteroaromatic fused rings (DPP pigments) to such eight-membered ring systems as flavanthrone or pyranthrone. The phthalo-cyanine skeleton with its polycylic metal complex is somewhat unique in this respect. 

Another approach is based on n-n stacking, which utilizes the moderately strong interactions between delocalized n-electrons of nanocarbons and those in aromatic organic compounds, such as derivatives of pyrene [54,55], porphyrins [56,57], phthalo-cyanines [58] or combinations thereof [59], as well as peptides [60], DNA [61], benzyl alcohol [62] or triphenylphosphine [63]. These molecules are often modified with long... 

Cyclic voltammetry revealed four reversible one-electron oxidation processes. The ground state structures for HOC and HOC " are aromatic . The structures for HOC" and HOC " are doublets and show Jahn-Teller distortions. The structures for HOC " in the solid is a Jahn-Teller distorted, closed-shell singlet with a canonical structure [37 ], as represented by cyanine/p-phenylenediammonium fragments. The one-to-one complex of HOC" TCNE" was indeed synthesized but found to be antiferromagnetic. 

An interesting equilibrium study was performed by Kasatani and coworkers on the interaction of a series of cyanine dyes with beta and gamma cyclodextrin, using u.v.-visible spectrophotometric measurements. The results were consistent with the enhancement of dimer formation by inclusion of the dye molecules within the cyclodextrin. As expected from the work of others, such geometrical factors " as the size of the aromatic groups and the lengths of the central methine chains strongly influence the occurrence of dimer formation within the cyclodextrin cavity. 

Scheme 1. Principle of cyanine dye synthesis leading to trimethine (n = l), pentamethine (n = 2) and heptamethine (n = 3) chromophores. Structures comprising indolic subunits are usually named indocarbocyanine, indodicarbocyanine and indotricarbocyanine, respectively. Formic acid, malonic aldehyde, glutaconic aldehyde are used in their protected dianUide or orthoester form. They can be applied as substituted derivatives to introduce residues into the polymethine unit. The indolic substructure might bear further residues or annelated aromatic rings...

Brightness. Brighmess of a fluorophore is proportional to the product of the molar absorption coefficient at the excitation wavelength times its quantum yield. This is the theoretical value, but in practice it can be much reduced by fluorescent quenching on interaction with other labels on the protein or DNA surfaces. Sulfonic acid groups on the aromatic rings of cyanines reduce this interaction, giving very much improved protein fluorescence. 

Several transition metal ions form stable complexes with aliphatic 1,2-dithiols, which absorb in the near-lR. Known as dithiolenes, their nickel complexes in particular have been found to have valuable properties. The physical properties of dithiolenes can be readily tailored by variations on the substituents attached to the dithiols, see (4.13). Although they have low molar absorption coefQcients, when compared to cyanines etc., they do have one big advantage in that they show very little absorption in the visible region." Stracturally analogous dyes can be made from aromatic dithiols and oxothiols (4.14), and the much more bathochromic naphthalene derivatives (4.15), but they are much weaker absorbers. 

Presumably, the dication obtained in sulfuric acid is a fully conjugated aromatic peripheral 22-jt system that forms 7-aggregates—previously observed exclusively in cyanine dyes. Only a few related compounds were found to give the same effect the structural requirement for 7-aggregation in these systems has been described (89CL1719). The optical properties of the corresponding propyl derivatives assembled in monolayers were studied (94MI4). 

Fig. 3. Bimolecular electron transfer of photoexcited donors and acceptors. The parabolas (a) and (i>) represent Eq. 1 with l = 0.42 eV. Curve (a) is flattened at the top due to the diffusional limit [27]. The Rehm-Weller equations (Eq. 6) with identical A is presented by lines (e) and (/), where the former includes a diffusional limit of kd = 2 x 1010 M 1 s"The filled circles represent the Rehm-Weller data for neutral aromatic donors and acceptors in acetonitrile [25]. The squares denote similar data for inorganic (charged) acceptors and organic (neutral) donors also in acetonitrile [28], The data are fitted into Eq. 6 with X = 0.69 eV and kd = 9 x 109 M 1 s "1 (line d). The open squares represent the forward ET to the excited inorganic complexes the filled squares depict the bimolecular BET within the photogenerated ion pairs of the same systems [28], The triangles represent forward electron transfer between organic borates [29] and cyanines (filled triangles) or pyrylium cations (open triangles) within contact ion pairs in benzene. Even in this case, without diffusional interference, the data seem to fit better the Rehm-Weller equation (g) than the Marcus equation (c)...

The doughnut geometry of the host was taken a step further by use of a functionally active spacer group. Instead of simple aromatic spacers previously used, phthalo cyanines were employed [155]. The geometry of the resulting dimer (65)2 is similar to that of the doughnut, and dimerisation is observed to be preferable in aromatic solvents which will fit the cavity and template the dimerisation process (Fig. 57). The use of the phthalo cyanine introduces a potential catalytic site within the capsule. To date, no work has been published investigating the catalytic potential of this dimer. 

Nonpolar solute in a nonpolar solvent. In this case, only dispersion forces contribute to the solvation of the solute. Dispersion forces, operative in any solution, invariably cause a small bathochromic shift, the magnitude of which is a function of the solvent refractive index n, the transition intensity, and the size of the solute molecule. The function (n — l)/(2n - -1) has been proposed to account for this general red shift [69, 70]. Corresponding linear correlations between this function of n and Av have been observed for aromatic compounds e.g. benzene [22], phenanthrene [71]), polyenes e.g. lycopene [23], y9-carotene [464]), and symmetrical polymethine dyes e.g. cyanines [26, 27, 292, 293]). 

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