The nature of electronic transitions in linear conjugated systems

Kachkovskii, A. D.

doi:10.1070/rc1997v066n08abeh000274

Cited by 87 publications

(97 citation statements)

References 139 publications

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“…The titration spectra in Figure 5 show one example: the appearance of a new absorption band at around 560 nm with a well-defined isosbestic point for SNO 3 in the presence of up to one equivalent of protons. In accordance with the shift observed upon exchange of one of the dimethylamino groups by a methoxy group, that is, exchange of a strong donor in SDMA with l abs max = 627 nm in chloroform for a weaker donor in USNO, absorbing at 579 nm; [48,49] we attribute this shift to exclusive protonation of one nitrogen atom. It is known that the small macrocycle in SNO 3 stabilises protonation of the nitrogen atom by hydrogen bonding interactions in nonprotic solvents.…”

Section: Wwwchemeurjorgsupporting

confidence: 84%

Squaraines as Reporter Units: Insights into their Photophysics, Protonation, and Metal‐Ion Coordination Behaviour

Ros‐Lis

Martínez‐Máñez

Sancenón

et al. 2008

Chemistry A European J

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The synthesis, photophysical properties, protonation, and metal-ion coordination features of a family of nine aniline-based symmetrical squaraine derivatives are reported. The squaraine scaffold displays very attractive photophysical properties for a signalling unit. These dyes show absorption and weakly Stokes-shifted, mirror-image-shaped emission bands in the visible spectral range and there are no hints of multiple emission bands. The mono-exponential fluorescence decay kinetics observed for all the derivatives indicate that only one excited state is involved in the emission. These data stress the interpretation that squaraines can be regarded as polymethine-type dyes. From a coordination chemistry point of view, the squaraines possess four potential binding sites; that is, two nitrogen atoms from the anilino groups and two oxygen atoms from the central C(4)O(2) four-membered ring. These coordination sites are part of a cross-conjugated pi-system and coordination events with protons or certain metal ions affect the electronic properties of the delocalised pi-system dramatically, resulting in a rich modulation of the colour of the squaraines. The absorption band at around 640 nm is blue-shifted when coordination at the anilino nitrogen atoms occurs, whereas coordination to the C(2)O(4) oxygen atoms results in the development of red-shifted bands. Addition of more than one equivalent of protons or metal cations could additionally entail mixed N,O- or N,N-coordinated complexes, manifested in the development of a broad band at 480 nm or complete bleaching in the visible range, respectively. Analysis of the spectrophotometric titration data with HYPERQUAD yielded the macroscopic and microscopic stability constants of the complexes. Theoretical modelling of the various protonated species by molecular mechanics methods and consideration of some of the title dyes within the framework of molecular chemosensing and molecular-scale "logic gates" complement this contribution.

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Section: Wwwchemeurjorgsupporting

confidence: 84%

Squaraines as Reporter Units: Insights into their Photophysics, Protonation, and Metal‐Ion Coordination Behaviour

Ros‐Lis

Martínez‐Máñez

Sancenón

et al. 2008

Chemistry A European J

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“…This was found to be dependent on the basicity of the terminal groups. [20] The values of the alternation of the bond lengths in the open PC of symmetrical dyes are calculated with Equation (1), in which l n is the length of the n-th bond in the open PC. These values are presented in Figure 1 (top).…”

Section: Dye Hetmentioning

confidence: 99%

Studies of 2‐Azaazulenium Derivatives: Unsymmetrical Trimethine Cyanine Dyes Bearing a 2‐Azaazulenium Moiety as One of the Terminal Groups

Bricks

Ryabitskii

Kachkovskii

2010

Chemistry A European J

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We report here the synthesis of a series of symmetrical and unsymmetrical trimethine cyanine dyes derived from 2-azaazulene, combined spectral and quantum-chemical investigations of their molecular geometry and electron structure, as well as the nature of the lowest electron transitions. Based on the analysis of both calculations and experimental data obtained from absorption and (13)C NMR spectra, it was concluded that the 2-azaazulene residue can be treated as a weakly basic terminal group; its donor properties are provided with the participation of the HOMO-1, in contrast to the typical Brooker's terminal residues with their donor HOMOs. The new classification of the terminal groups of cyanine dyes, and hence the classification of types of unsymmetrical cyanines, is proposed. It is shown that the nature of the higher electron transitions (delocalized or local) in the cyanine dyes depends on their type. In the unsymmetrical trimethine cyanine of the mixed type, negative deviations are observed in their absorption spectra.

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“…The terminal groups (TGs) in cyanine chain are the major sites of substitutions. The modifications in different ways and the presence of appended charged groups do not influence the alternating π-electron density distribution in the main chain [17,83].…”

Section: Why Cyanine Dyes?mentioning

confidence: 99%

Fluorescent J-aggregates of cyanine dyes: basic research and applications review

Bricks

Slominskii

Panas

et al. 2017

Methods Appl. Fluoresc.

340

299

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J-aggregates are fascinating fluorescent nanomaterials formed by highly ordered assembly of organic dyes with the spectroscopic properties dramatically different from that of single or disorderly assembled dye molecules. They demonstrate very narrow red-shifted absorption and emission bands, strongly increased absorbance together with the decrease of radiative lifetime, highly polarized emission and other valuable features. The mechanisms of their electronic transitions are understood by formation of delocalized excitons already on the level of several coupled monomers. Cyanine dyes are unique in forming J-aggregates over the broad spectral range, from blue to near-IR. With the aim to inspire further developments, this review is focused on the optical characteristics of J-aggregates in connection with the dye structures and on their diverse already realized and emerging applications.

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The nature of electronic transitions in linear conjugated systems

Cited by 87 publications

References 139 publications

Squaraines as Reporter Units: Insights into their Photophysics, Protonation, and Metal‐Ion Coordination Behaviour

Squaraines as Reporter Units: Insights into their Photophysics, Protonation, and Metal‐Ion Coordination Behaviour

Studies of 2‐Azaazulenium Derivatives: Unsymmetrical Trimethine Cyanine Dyes Bearing a 2‐Azaazulenium Moiety as One of the Terminal Groups

Fluorescent J-aggregates of cyanine dyes: basic research and applications review

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