New conjugates of fluorophore based on 3,4-dimethoxy-4-styryl-1,8-naphthalimide and photosensitizer bacteriochlorinediffering in the nature of spacer fragments were synthesized and their spectral-luminescent properties were studied. The conjugates efficiently generate singlet oxygen in solution, however, the emission of the naphthalimide fragment of the conjugates is quenched to varying degrees as a result of the photoexcitation energy transfer to bacteriochlorin.

Novel 2-(2-hydroxyphenyl) substituted imidazoles have been synthesized. A prototropic tautomerism of the 1-hydroxyimidazole derivatives has been studied. X-ray diffraction analysis and IR-spectroscopy have revealed that in the solid state the title compounds exist as the N-hydroxy tautomers. The 1H and 13C NMR spectra of the new imidazole derivatives are discussed. It has been shown that in chloroform solutions 5-carbonyl substituted 2-(2-hydroxyphenyl)-1-hydroxyimidazoles exist in the N-hydroxy tautomeric form. A transition to DMSO results in the existence of the 1-hydroxyimidazoles under study as the N-oxide tautomers.

New 4-methoxy-1,8-naphthalimide derivative containing a salicylideneamino receptor group at the imide nitrogen atom demonstrated selective fluorescent response to Zn2+ cations due to the formation of 1: 2 and 2: 1 ligand–metal complexes.

New 4-methoxy-1,8-naphthalimide derivative equipped with bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetate receptor moiety at the imide nitrogen atom showed a fluorescent response to Ca2+ cations due to the formation of complexes of 1:1 ligand–metal composition.

Conjugation of 4-pyrazolinyl-1,8-naphthalimide and propargyl-15(2),17(3)-dimethoxy-13(1)-amide of bacteriochlorin e by the oligo(ethylene glycol) linker resulted in the dual function system comprising the modalities of a photosensitizer and a fluorescence imaging agent. In comparison with the conjugate of the same structure but containing the shorter linker, the system demonstrated the higher emission intensity originating from the naphthalimide unit, which could be explained by the decrease in resonance energy transfer efficiency between the chromophores. It has been shown that the ability of bacteriochlorin to generate singlet oxygen remains at the same level when this fragment is introduced in the conjugate structure. 4-Pyrazolinyl-1,8-naphthalimide group in the studied compounds was found to easily undergo photooxidation yielding highly emissive 4-pyrazolyl-1,8-naphthalimide derivatives.

A novel approach to the synthesis of pH-sensitive prodrugs has been proposed: thiourea drug modification. Resulting prodrugs can release the cytotoxic agent and the biologically active 2-thiohydantoin in the acidic environment of tumor cells. The concept of acid-catalyzed cyclization of thioureas to 2-thiohydantoins has been proven using a FRET model. Dual prodrugs of model azidothymidine, cytotoxic doxorubicin, and 2-thiohydantoin albutoin were obtained, which release the corresponding drugs in the acidic environment. The resulting doxorubicin prodrug was tested on prostate cancer cells and showed that the thiourea-modified prodrug is less cytotoxic (average IC50 ranging from 0.5584 to 0.9885 μM) than doxorubicin (IC50 ranging from 0.01258 to 0.02559 μM) in neutral pH 7.6 and has similar toxicity (average IC50 ranging from 0.4970 to 0.7994 μM) to doxorubicin (IC50 ranging from 0.2303 to 0.8110 μM) under mildly acidic conditions of cancer cells. Cellular and nuclear accumulation in PC3 tumor cells of Dox prodrug is much higher than accumulation of free doxorubicin.

Theranostic upconversion nanoparticles (UCNPs) are ideal candidates for personalized medicine. We present a smart, easy-to-prepare nanohybrid (NH) suitable for NIR-theragnosis and imaging tracking without triggering therapy simultaneously. The photophysical features of each component have been carefully selected in order to maximize the capabilities for theragnosis, in particular, the upconversion emission and the photosensitizer absorption. In addition, NH presents a fluorescent marker with one-photon absorption in the green and two-photon absorption cross-section at NIR wavelengths where the UCNP does not absorb, thus enabling innocuous tracking. Thus, the NH consists of NaYF4:Yb, Er, Tm (UCYbErTm) emitting in the UV, vis, and NIR; a broadband-absorbing natural porphyrin (PP) in the UV-to-NIR range but from 580 to 675 nm; and a 1,8-naphthalimide (NI) with two absorption bands (UV, VIS), and dual emission. In vitro assays demonstrate that UCYbErTm@PP/NI NH is noncytotoxic and extremely effective for NIR-induced cancer cell death. Moreover, this NH offers fluorescence tracking features without therapy due to the specific excitation of NI in the NIR and emission in the orange. This strategy opens up new alternatives for successful and noninvasive antitumoral theragnosis

The Photosensitizing and fluorescence imaging ability of a bacteriochlorin–naphthalimide conjugate is studied.

The photophysical properties of naphthalimide dyes NI1-3 with electron releasing 4-methoxy-(NI1), 3,4-dimethoxystyryl-(NI2) and dimethylaminostyryl (NI3) groups are examined in a variety of protic and aprotic solvents. All compounds demonstrate positive solvatochromism in the steady-state absorption and fluorescence spectra. The analysis of the dependence of the Stokes shift on the polarity of the solvent using the Lippert-Mataga equation allowed us to determine the change in the dipole moment upon excitation. The obtained data correspond to the formation of highly polar charge transfer states. Based on the transient absorption spectra and time-resolved fluorescence measurements, the presence of two different emissive states was definitely proved. The primarily formed planar Local Excited (LE) state dominates in non-polar solvents like cyclohexane and toluene where it relaxes mostly through fluorescence and E, Z-isomerisation pathways. In polar solvents, an alternative relaxation channel emerges that consists of twisting around single bond between styryl and naphthalimide fragments, which leads to the formation of a Twisted Intramolecular Charge Transfer (TICT) state. The factors affecting the fluorescence of TICT states are discussed. The observed spectral effects are rationalized using quantum-chemical calculations, X-ray data and NMR spectroscopy.

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.