Series Of Polymethine Dyes Research Articles

Quantum–Classical Mechanics: Nano-Resonance in Polymethine Dyes

It is well known in quantum mechanics that the theory of quantum transitions is based on the convergence of the series of time-dependent perturbation theory. This series converges in atomic and nuclear physics. However, in molecular and chemical physics, this series converges only in the Born–Oppenheimer adiabatic approximation and due to the application of the Franck–Condon principle, and it diverges as a result of going beyond the adiabatic approximation and the Franck–Condon principle. This divergence (singularity) is associated with the incommensurability of the masses of light electrons and heavy nuclei which jointly participate in the full-fledged movement in the transient state of molecular “quantum” transitions. In a new physical theory—quantum–classical mechanics (Egorov, V.V. Heliyon Physics 2019, 5, e02579)—this singularity is damped by introducing chaos into the transient state. This transient chaos is introduced by replacing the infinitely small imaginary additive in the energy denominator of the spectral representation of the total Green’s function of the system with a finite value and is called dozy chaos. In this article, resonance at the nanoscale (nano-resonance) between electron and nuclear reorganization motions in the quantum–classical (dozy-chaos) mechanics of elementary electron transfers in condensed media and their applications to polymethine dyes and J-aggregates in solutions are reviewed. Nano-resonance explains the resonant character of the transformation of the shape of the optical absorption band in a series of polymethine dyes in which the length of the polymethine chain changes, as well as the nature of the red-shifted absorption band of the J-aggregates of polymethine dyes (J-band), which is narrow and intense. The process of dye aggregation in an aqueous solution with an increase in its concentration by the formation of J-aggregates is considered a structural tuning of the “polymethine dye + environment” system into resonance with light absorption. For J-aggregates in Langmuir films, the asymmetry of the luminescence and absorption bands, as well as the small value of their Stokes shifts, are explained. The parasitic transformation of the resonant shape of the optical absorption band of a polymethine dye in solution during the transition from one-photon to two-photon absorption is also explained, and the conditions for the restoration of this nano-resonance shape are predicted.

Polymethine Thiopyrylium Fluorophores with Absorption beyond 1000 nm for Biological Imaging in the Second Near-Infrared Subwindow.

Small-molecule fluorescence imaging in the second near-infrared (NIR-II, 1000-1700 nm) window has gained increasing interest in clinical application. Till now, very few studies have been exploited in the small-molecule fluorophores with both excitation and emission in the NIR-II window. Inspired by the indocyanine green structure, a series of polymethine dyes with both absorption and emission in the NIR-II window have been developed for NIR-II imaging, providing the feasibility to directly compare optical imaging in the NIR-IIa (1300-1400 nm) subwindow under 1064 nm excitation with that in the NIR-II window under 808 nm excitation. The signal-background ratio and the tumor-normal tissue ratio achieved great improvement under 1064 nm excitation in the imaging of mouse blood pool and U87 glioma tumors. Our study not only introduces a broadband emission fluorophore for both NIR-II and NIR-IIa imaging, but also reveals the advantages of NIR-II excitation over NIR-I in in vivo imaging.

Electronic transitions in polymethine dyes involving local and delocalized levels

Several series of polymethine dyes containing terminal groups, which can generate the local levels close to the HOMO/LUMO energy gap, have been investigated by spectroscopic and quantum-chemical methods. The analysis of the obtained data has shown that the participation of the local levels in the electronic transitions leads to the appearance of the specific quasi-local transitions which differ from the transitions between delocalized molecular orbitals by their sensitivity to the length of the π-conjugated chromophore and to the chemical constitution of the terminal groups. These quasi-local transitions can be experimentally detected by measuring of the ordinary absorption spectra or by the excitation anisotropy spectra, in case when their low-intensive bands are covered by the intensive absorption band. In the unsymmetrical dyes, containing different terminal groups, the delocalized and quasi-local transitions can be mixed producing complicated absorption spectra with two comparatively intensive bands, and their shapes can be gradually transformed upon the lengthening of the π-conjugated chromophore.

Excited-state absorption dynamics in polymethine dyes detected by polarization-resolved pump–probe measurements

Polarization-resolved excitation-probe measurements are performed for a new series of polymethine dyes in several solvents and a polyurethane acrylate elastopolymer. We describe our experimental studies and give an analysis of the nature of the rotational motions of excited molecules and orientation of the excited-state transitions relative to transitions from the ground state.

Alternative Compounds for the Particle in a Box Experiment

A new series of compounds is proposed to serve as an experimental example of the one-dimensional particle in a box model. The compounds studied are: 1,4-diphenyl-1,3-butadiene, 1,6-diphenyl-1,3,5-hexatriene, and 1,8-diphenyl-1,3,5,7-octatetraene. In all three compounds the distance between the phenyl groups is taken as the length of the one-dimensional box. The lowest energy peak in the ultraviolet absorption spectrum corresponds to the lowest energy transition in the molecule and is used to determine the experimental length of the box. The experimental box length agrees well with the box length determined from average bond length data and the percent errors are similar to those obtained when a series of polymethine dyes are used to represent the box.

A study of the vinylene shifts in polymethine dyes with sulphur-containing end-groups

A series of polymethine dyes with sulphur-containing end-groups have been investigated by spectral and quantum-chemical methods. The shift in absorption maximum with lengthening of the polymethine chain has been shown to depend on the nature of the first member of the vinylene series. Possible causes of this are discussed and a correlation between the first vinylene shift and the electron density change on excitation at the sulphur atoms has been established.

Long chain heterocyclic dyes. Part one. Hydrophobic structures

AbstractA series of polymethine dyes and of their precursors, containing long and short alkyl chains, was prepared and their chemical and spectroscopic (uv, 1H‐nmr) properties were briefly discussed. The electronic absorption spectra of the dyes in aqueous medium and in presence of anionic or cationic surfactants evidenced aggregation phenomena. The best deaggregating effect was shown by the anionic surfactant when added above its critical micellar concentration.

Laser action and photoisomeric transformations in polymethine dyes

A study was made of stimulated emission from a series of polymethine dyes, differing in respect of the radical incorporated in the polymethine chain, and of the effect of photoisomeric transformations in excited states on the emission. The absorption spectra of the photoisomers and their lifetimes in the nonequilibrium state were determined. An energy level scheme was deduced and the channeb of radiative and nonradiative transitions in this series of dyes were identified.