2-((E)-2-((E)-4-Chloro-5-(2-((E)-5-methoxy-3,3-dimethyl-1-(3-phenylpropyl)indolin-2-ylidene) ethylidene)-1,1-dimethyl-1,2,5,6-tetrahydropyridin-1-ium-3-yl)vinyl)-5-methoxy-3,3-dimethyl-1-(3-phenylpropyl)-3H-indol-1-ium

A heptamethine fluorophore, ERB-60, has been synthesized efficiently in four steps in a good yield. The structure of this fluorophore consists of an electron-donating group (methoxy), a hydrophobic moiety (phenylpropyl) with a rotatable bond, a quaternary ammonium fragment, and indolium rings at the terminal ends connected via polymethine chain. All these inherent chemical features fine-tuned the optical properties of the fluorophore. This compound was characterized by both 1H NMR, 13C NMR and mass spectra. The optical properties, including molar absorptivity, fluorescence, Stokes’s shift, and quantum yield, were measured in different solvents such as DMSO, DMF, MeCN, i-PrOH, MeOH, and H2O. The wavelengths of maximum absorbance of ERB-60 were found to be in the range of 745–770 nm based on the solvents used. In decreasing order, the maximum wavelength of absorbance of ERB-60 in the tested solvents was DMSO > DMF > i-PrOH > MeOH > MeCN > H2O while the decreasing order of the extinction coefficient was found to be MeCN > MeOH > DMSO > i-PrOH > H2O > DMF. ERB-60 was found to be more photostable than IR-786 iodide, a commercially available dye, and brighter than the FDA-approved dye, indocyanine green (ICG).

Near-Infrared-II Cyanine/Polymethine Dyes, Current State and Perspective

The development of near-infrared-II (NIR-II) fluorescence imaging has implemented real-time detection of biological cells, tissues and body, monitoring the disease processes and even enabling the direct conduct of surgical procedures. NIR-II fluorescence imaging provides better imaging contrast and penetration depth, benefiting from the reducing photon scattering, light absorption and autofluorescence. The majority of current NIR-II fluorophores suffer from uncontrollable emission wavelength and low quantum yields issues, impeding the clinical translation of NIR-II bioimaging. By lengthening the polymethine chain, tailoring heterocyclic modification and conjugating electron-donating groups, cyanine dyes have been proved to be ideal NIR-II fluorophores with both tunable emission and brightness. However, a simpler and faster method for synthesizing NIR-II dyes with longer wavelengths and better stability still needs to be explored. This minireview will outline the recent progress of cyanine dyes with NIR-II emission, particularly emphasizing their pharmacokinetic enhancement and potential clinical translation.

Streptocyanine dyes

The simplest possible type of polymethine dye consists of an odd-numbered polymethine chain sandwiched between two terminal nitrogen atoms, which do not form part of an unsaturated heterocyclic ring. Originally, this type of colorant was termed streptopolymethine dyes. For systematic reasons they are usually called streptocyanine dyes today. Their color is mainly determined by the lengths of their polymethine chains. Owing to their simple structure they are the favorite compounds for investigation of fundamental structure–property relationships. In the form of dianil hydrochlorides mainly streptocyanines are used to prepare cyanine, hemicyanine, merocyanine, oxonol, pyrylium and thiopyrylium dyes.

Apocyanine dyes

Cyanine dyes without a methine group or polymethine chain between their two terminal unsaturated heterocycles are called apocyanines. Such colorants which are yellow and red received the labels xantho-apocyanine and erythro-apocyanine dyes, respectively. Nevertheless, from time to time in the literature, the term “apocyanine dyes” is wrongly applied to various N-bridgehead heterocycles. In addition, the phenylogous zeromethine hemicyanine dyes are often incorrectly referred to with the term “apocyanine dyes”. This chapter clarifies the definition of apocyanine, describes how confusion over the term has come about, and points the ways in which it is sometimes incorrectly employed.

Nature of Lowest Electron Transitions in Anionic Polymethine Dyes With Keto-Containing Terminal Groups

The complex quantum-chemical and spectral study of the anionic polymethine dyes with the simplest symmetrical terminal groups and with different length polymethine chain is performed. It was shown that these dyes produce the specific molecular orbitals positioned nearly the energy gap and located only within the terminal groups. By investigation of the absorption spectra, it was established that the typical highly intensive longwawelength spectral band is observed which are bathochromically shifted upon lengthening of the open conjugated chain; this polymethine band is connected with the electron transition between the frontier levels of the opposite symmetry. In the contrast, the local MOs take part in so-called quasi-local electron transitions involved also one the frontier orbital. The local transitions have small dipole moments and hence they do practically not appear in the absorption spectra, however, the local transitions cause the appearance of the non-deep minima in the spectra of the fluorescence excitation anisotropy.

Электронное строение и спектрально-флуоресцентные свойства лазерных красителей тиопирило-4-трикарбоцианинов

It was found that the long-wavelength absorption band of the laser dye IR 1061 and its analogue with an unsubstituted polymethine chain is strongly broadened and decreases in intensity in polar solvents, while the fluorescence band remains narrow and practically does not change in a wide range of solvent polarities. Based on the quantum-chemical calculations of these dyes by the ab initio DFT/B3LYP/6-31G (d,p) and TDDFT methods, taking into account the polarity of the medium by the PCM method, it is shown that the reason for this difference is the weakening of solvation in the fluorescent state as compared to the ground state due to the greater equalization of the charge in the first than in the latter. An increase in the alternation of bond orders in the polymethine chain in the fluorescent state was found, which causes an increase of vibronic interactions in the radiative transition as compared to the absorptive one. Spectral effects caused by a change in the angle of rotation of phenyl groups in the thiopyrylium cycle upon excitation have been analyzed.

High-efficiency polymethine dyes for passive Q-switch and mode locking of neodymium lasers

New polymethine dyes (PD) based on benzene [c, d] indole were synthesized. Their spectral and nonlinear optical characteristics in liquid and polymer media have been studied. It was found that the relaxation times τ of the excited state of the new PDs are approximately the same as those of the dye 3274y, which is widely used as a passive Q-switch of neodymium lasers with a generation lengthwave of 1.06 μm. The low sensitivity of τ to changes in the chemical structure of such PDs indicates that the main contribution to the deactivation of the excited state is made by the benzene [c, d] indole heterocycle. High values ​​of the cross section in the range of 1.05-1.08 μm at low relaxation times allow the studied PD to be easily bleached in lasers at low intensities (about 10 MW/cm2). It is established that the photostability of the new PD significantly exceeds that for the dye 3274y. This is because they contain a saturated six-membered ring in the polymethine chain, which is much less reactive than the corresponding five-membered ring of dye 3274u with respect to the photoinitiator of free radicals of UV irradiation. It is shown that the efficiency of Q-switching and mode locking of new passive laser shutters is higher than their analogues based on the dye 3274y.

IR Luminescence of Polyfunctional Associates of Indocianine Green and Ag-=SUB=-2-=/SUB=-S Quantum Dots-=SUP=-*-=/SUP=-

In this work, manifestations of IR luminescence sensitization of Indocyanine Green during conjugation with colloidal Ag2S quantum dots with average size of 2.2 and 3.7 nm, passivated with thioglycolic acid molecules (Ag2S/TGA QDs) are studied using absorption and luminescence techniques. The possibility of enhancing luminescence in the dye monomer band (820 nm) under excitation of 660 nm by a factor of 6 in the presence of Ag2S/TGA QDs (2.2 nm) due to a decrease in the dye polymethine chain due movement via coordination interaction with quantum dots was demonstrated. The way to switch-over from the first therapeutic window of biological tissue transparency (NIR-I, 700-950 nm) to the second (NIR-II, 1000-1700 nm), based on sensitization of IR luminescence of Ag2S/TGA QDs with an average size of 3.7 nm in the region of 1040 nm due to of resonance non-radiative transfer of excitation energy from Ag2S/TGA (2.2 nm) QDs at 900 nm to Ag2S/TGA QDs (3.7 nm) via the J-aggregate of ICG dye, which acts as an exciton bridge.

Polymethine dyes

There are a lot of different dye classes with complete different chemical structures. On the basis of a common classification the term “polymethine dyes” was created in 1926. Common criteria are a conjugated polymethine chain with terminal functional groups and an odd number 2n + 3 of π-centers and 2n + 4 π-electrons (n is the number of vinyl groups), the vinylene shift of the 0–0 vibronic transition of about 100 nm per vinyl group, the influence of substituents or heteroatoms according to Dewar´s Rules and a bathochromic shift by twisting of the polymethine chain according to the Brunings–Corwin effect.

CRYSTAL STRUCTURE AND TAUTOMERISM OF ALKYLAMINO-β-KETOENOLS IN SOLUTIONS

The structure of alkylamino-β-ketoenols obtained by opening of the pyran cycle of chalcones based on dehydracetic acid was studied by X-ray diffraction, IR, 1H NMR spectroscopy and chromatography-mass spectrometry. The infrared spectra of the compounds appear to be typical of β-ketoenols. The crystalline structure (2Z,5Z,7E,9E)-6-hydroxy-2-(methylami-no)-10-phenylethoxy-2,5,7,9-tetraene-4-one was first determined. A comparative analysis of it with 2 pre-viously published structures has been carried out. All of these compounds are crystallized in the form of yellow plates in the monoclinic crystalline system (spatial group P21/n), they have a planar arrangement of the polyene chain and β-ketoenol fragment con-jugated to the aromatic ring. It has been established that the planar configuration of the β-ketoenol fragment is stabilized by hydrogen bonds between the hydroxy and keto group and the amino and keto group in the crystalline state. The length of the polymethine chain, the nature of the substituents in the aromatic and aliphatic part of the molecule do not significantly affect the size and geometry of the alkylamino-β-ketoenolate fragment. Approximately the same lengths of bonds, the distance between atoms and the corners indicate that all these com-pounds may have similar chelating properties. Ac-cording to 1H NMR spectroscopy in various deu-terated solvents (benzene, DMSO, chloroform, ace-tone, methanol and trifluoroacetic acid), most of the main signals of the obtained compounds have sa-tellites, which indicates the existence of several isomeric forms in solutions. The analysis of integral intensities of labile protons in 1H NMR spectra does not allow to obtain accurate results regarding the ratio of tautomers in a solution, but for a series of compounds their approximate ratio in chloroform, DMSO and trifluoroacetic acid have been established (from 70:30 in CDCl3 to 90:10 in DMSO and CF3CO2D). The stability of the tautomers in the solutions is confirmed by the data of chromatogra-phy-mass spectrometry.