Pavel A. Panchenko

Cation-dependent fluorescent properties of naphthalimide derivatives with N-benzocrown ether fragment.

The investigation of N-phenyl-4-amino- and N-phenyl-4-acetamido-1,8-naphthalimides containing N-benzo-15-crown-5 ether substituent showed that the presence of ionophoric fragment as N-substituent in naphthalimide molecule provides the design of compound possessing the properties of fluorescent receptor. The addition of metal cations does not change the position of absorption and emission bands but substantial increases the fluorescence intensity. The study of molecules included the theoretical and experimental (optical, NMR) methods, analysis of intramolecular charge (electron) transfer and fluorescence properties in the presence and absence of metal ions.

Spectroscopical study of bacteriopurpurinimide-naphthalimide conjugates for fluorescent diagnostics and photodynamic therapy.

Two novel bis(chromophoric) dyads ABPI-NI1 and ABPI-NI2 containing 1,8-naphthalimide and bacteriopurpurinimide units linked by p-phenylene-methylene (ABPI-NI1) and pentamethylene (ABPI-NI2) spacers were prepared to test their ability to be used in the design of effective agents for both photodynamic therapy (PDT) and fluorescent tumor imaging. Photophysical studies revealed that the emission from the naphthalimide chromophore in both conjugates was partially quenched due to resonance energy transfer between the photoactive components. Compound ABPI-NI2 with more sterically flexible oligomethylene group demonstrated higher fluorescence intensity as compared with that for ABPI-NI1.

Synthesis and sensor propeties of crown-containing derivatives of 4-(1,5-diphenyl-Δ2-pyrazolin-3-yl)-1,8-naphthalimide

Previously undescribed derivatives of 4-(1,5-diphenyl-Δ2-pyrazoline-3-yl)-1.8-naphthalimide that contain a moiety of benzo-15-crown-5- and N-phenylaza-15-crown-5-ether in the composition of the N-aryl substituent at the imide nitrogen atom of the naphthalimide nucleus have been synthesized. The derived compounds have a long-wavelength band in the absorption spectra in the region of 480 nm owing to charge transfer from the electron-donor pyrazoline moiety onto the carbonyl groups of the carboxyimide group. The fluorescence peaks are located in the region of 670 nm. In the series of the synthesized pyrazolinylnaphthalimides, the effect of the nature of the N-aryl moiety on the spectral-luminescent properties has been analyzed. It has been shown that the annelation of the 15-crown-5-ether moiety with the benzene ring of the N-phenyl substituent of 4-pyrazolinyl-N-phenyl naphthalimide does not change the position of bands in the absorption and fluorescence spectra and has little effect on the fluorescence quantum yield. At the same time, the presence of the N-phenylaza-15-crown-5-ether group in the composition of the N-aryl moiety leads to a small hypsochromic shift of the peaks in the absorption and emission spectra and to a decrease in fluorescence intensity attributed to the occurrence of a nonradiative process of electron transfer from the N-aryl substituent onto the photoexcited naphthalimide chromophore. The proposed explanation for the observed spectral effects has been confirmed by the data of semi-empirical quantum-chemical calculations using the PM6 method. The complexation of crown-containing 4-pyrazolinylnaphthalimides was studied employing alkaline earth metal cations (Mg2+ and Ca2+) in acetonitrile solutions. 1H NMR spectroscopy has revealed that the coordination of the cation occurs through the crown-ether receptor. Upon complexation, in the absorption and fluorescence spectra, a bathochromic shift of the peaks of the long-wavelength bands by 6–15 nm was observed. The binding of the Mg2+ cations by the benzo-15-crown-5-ether derivative of naphthalimide was accompanied by fluorescence quenching, while in the case of 4-pyrazolinylnaphthalimide containing an N-phenylaza-crown-ether moiety in the N-aryl substituent, during the complexation with the Ca2+ cations, fluorescence buildup was observed. The spectrofluorometric titration data were used to determine the stability constants of complexes of crown-containing naphthalimides with alkaline earth metal cations with a composition of 1: 1 in acetonitrile. These studies have shown that the synthesized compounds are promising from the standpoint of developing fluorescent sensors for cation analysis.

Utilizing a pH‐Sensitive Dye in the Selective Fluorescent Recognition of Sulfate

A receptor containing amidopyrrole binding subunits and free amino groups, conjugated to a naphthalimide dye, has been designed and synthesized. The intrinsic selectivity of the binding motif for phosphate present in DMSO completely disappears in 10 % DMSO aqueous buffer at pH 3.6, at which the receptor is protonated. The electrostatic interactions between the receptor and an anion start to dominate, thus leading to selectivity for sulfate. The ability of the HSO4- anion to transfer the proton to the amino group during the recognition event suppresses the photoinduced electron transfer (PET) on the dye, resulting in a selective turn-on fluorescent response. The choice of pH of the solution for sensing is dictated by the pKa value of the dye.

Synthesis and spectral properties of fluorescent dyes based on 4-styryl-1,8-naphthalimide

The paper reports on synthesis and spectroscopic study of novel N-butyl-4-styryl-1,8-naphthalimide dyes bearing methoxy (1), dimethoxy (2), and dimethylamino (3) groups in the styryl fragment. It is shown that all synthesized compounds demonstrate positive solvatochromism, high values of Stokes shift in polar solvents, and fluorescence in the long wavelength part of visible range. These facts indicate a potential application of these compounds as fluorescent dyes in the biochemistry. The changes in the dipole moments of the molecules caused by excitation were estimated using Lippert—Mataga equation. The obtained results could be assigned to the formation of the excited states with intramolecular charge transfer. The formation of the twisted states with charge transfer was suggested in the case of compound 3, while the fluorescence quantum yield was significantly reduced in polar protic solvents.

Cation-dependent spectral properties of fluorescent complexon based on 1,8-naphthalimide with PET mechanism of optical response

Complexation of 4-amino-1,8-naphthalimide derivative containing an aza-15-crown-5 ether receptor unit in the N-aryl substituent at the imide nitrogen atom of the naphthalimide core with alkaline earth metal cations was studied using optical and NMR spectroscopy. The binding of the cations with crown ether receptors was accompanied by signifacant fluorescence enhancement of naphthalimide moiety caused by the inhibition of the photoinduced electron transfer (PET) process. An increase in the cation radii on going from Mg2+ to Ca2+ to Ba2+ leads to a decrease in the complex stability and an increase in the quantum yield of its fluorescence.