Facile synthesis, sensor activity and logic behaviour of 4-aryloxy substituted 1,8-naphthalimide

Synthesis and Biological Properties of Fluorescent Strigolactone Mimics Derived from 1,8-Naphthalimide

Strigolactones (SLs) have potential to be used in sustainable agriculture to mitigate various stresses that plants have to deal with. The natural SLs, as well as the synthetic analogs, are difficult to obtain in sufficient amounts for practical applications. At the same time, fluorescent SLs would be useful for the mechanistic understanding of their effects based on bio-imaging or spectroscopic techniques. In this study, new fluorescent SL mimics containing a substituted 1,8-naphthalimide ring system connected through an ether link to a bioactive furan-2-one moiety were prepared. The structural, spectroscopic, and biological activity of the new SL mimics on phytopathogens were investigated and compared with previously synthetized fluorescent SL mimics. The chemical group at the C-6 position of the naphthalimide ring influences the fluorescence parameters. All SL mimics showed effects similar to GR24 on phytopathogens, indicating their suitability for practical applications. The pattern of the biological activity depended on the fungal species, SL mimic and concentration, and hyphal order. This dependence is probably related to the specificity of each fungal receptor-SL mimic interaction, which will have to be analyzed in-depth. Based on the biological properties and spectroscopic particularities, one SL mimic could be a good candidate for microscopic and spectroscopic investigations.

Design and Synthesis of a Novel ICT Bichromophoric pH Sensing System Based on 1,8-Naphthalimide Fluorophores as a Two-Input Logic Gate and Its Antibacterial Evaluation

The synthesis, sensor activity, and logic behavior of a novel 4-iminoamido-1,8-naphthalimide bichromophoric system based on a "fluorophore-receptor" architecture with ICT chemosensing properties is reported. The synthesized compound showed good colorimetric and fluorescence signaling properties as a function of pH and proved itself as a promising probe for the rapid detection of pH in an aqueous solution and base vapors in a solid state. The novel dyad is able to work as a two-input logic gate with chemical inputs H⁺ (Input 1) and HO^- (Input 2) executing INHIBIT logic gate. The synthesized bichromophoric system and the corresponding intermediates demonstrated good antibacterial activity toward Gram (+) and Gram (-) bacteria when compared with the Gentamycin standard.

TICT compounds by design: comparison of two naphthalimide-π-dimethylaniline conjugates of different lengths and ground state geometries

Two new twisted intramolecular charge transfer (TICT) donor-π-acceptor compounds were designed by combining a well-known electron acceptor naphthalimide unit with a classic electron donor dimethylaniline through two types of different rigid linkers. The combined steady-state and time-resolved spectroscopy of molecules in solvents of different polarities in comparison to solid-state solvation experiments of doped polymer matrixes of different polarities allowed distinguishing between solvation and conformation determined processes. The photophysical measurements revealed that non-polar solutions possess high fluorescence quantum yields of up to 70% which is a property of pre-twisted/planar molecules in the excited charge transfer (CT) states. The increase of polarity allows tuning the Stokes shift through all the visible wavelength range up to 8601 cm^-1 which is accompanied by a three orders of magnitude drop of fluorescence quantum yields. This is a result of the emerged TICT states as dimethylaniline twists to a perpendicular position against the naphthalimide core. The TICT reaction of molecules enables an additional non-radiative excitation decay channel, which is not present if the twisting is forbidden in a rigid polymer matrix. Transient absorption spectroscopy was employed to visualize the excited state dynamics and to obtain the excited state reaction constants, revealing that TICT may occur from both the Franck-Condon region and the solvated pre-twisted/planar CT states. Both molecules undergo the same photophysical processes, however, a longer linker and thus a higher excited state dipole moment determines the faster excited state reactions.

A Highly Water-Soluble and Solid State Emissive 1,8-Naphthalimide as a Fluorescent PET Probe for Determination of pHs, Acid/Base Vapors, and Water Content in Organic Solvents

A new highly water-soluble 1,8-naphthalimide fluorophore designed on the “fluorophore-spacer-receptor1-receptor2” model has been synthesized. Due to the unusually high solubility in water, the novel compound proved to be a selective PET-based probe for the determination of pHs in aqueous solutions and rapid detection of water content in organic solvents. Based on the pH dependence of the probe and its high water solubility, the INH logic gate was achieved using NaOH and water as chemical inputs, where NaOH is the disabler and the water is an enabler. In addition, the probe showed effective fluorescence “off-on” reversibility on glass support after exposure to acid and base vapors, which defines it as a promising platform for rapid detection of acid/base vapors in the solid-state, thus extending the molecular sensing concept from solution to the solid support.

Synthesis and Solvent Dependent Fluorescence of Some Piperidine-Substituted Naphthalimide Derivatives and Consequences for Water Sensing

Novel fluorescent strigolactone derivatives that contain the piperidine-substituted 1,8-naphthalimide ring system connected through an ether link to a bioactive 3-methyl-furan-2-one unit were synthesized and their spectroscopic properties investigated. The solvatochromic behavior of these piperidine-naphthalimides was monitored in solvents of different polarity using the electronic absorption and fluorescence spectra. These compounds exhibited a strong positive solvatochromism taking into account the change of solvent polarity, and the response mechanism was analyzed by fluorescence lifetime measurements. According to Catalan and [f(n), f(ε), β, α] solvent scales, the dipolarity and polarizability are relevant to describe the solute-solvent interactions. The emission chemosensing activity was discussed in order to determine the water content in organic environments. The emission intensity of these compounds decreased rapidly in dioxane, increasing water level up to 10%. Measuring of quantum yield indicated that the highest values of quantum efficiency were obtained in nonpolar solvents, while in polar solvents these derivatives revealed the lowest quantum yield. The fluorescence decay can be described by a monoexponential model for low water levels, and for higher water contents a biexponential model was valid.

The study of chiral recognition on ibuprofen enantiomers by a fluorescent probe based on β-cyclodextrin modified ZnS:Mn quantum dots

In this paper, a fluorescence method for chiral detection of ibuprofen and its enantiomer was developed. The L-cystenine-capped ZnS:Mn quantum dots were synthesized and functionalized with β-cyclodextrin (β-CD-QDs). The β-CD-QDs exhibited different quenching effect to the S-(+)-ibuprofen and the R-(-)-ibuprofen based on the advantage of the inclusion complex of cyclodextrin. It was found that the quenching of β-CD-QDs by S-(+)-ibuprofen was due to the formation of inclusion complex through both static quenching and photoinduced electron transfer, but only slight quenching with the R-(-)-ibuprofen. The stability constants derived from Hildebrand-Benesi method and absorption titration experiments were applied to determine the stability constants of the formed complexes, the double reciprocal plots suggest that a conclusion complex with a ratio of 1:1 was formed between β-CD-QDs and S-(+)-ibuprofen, but did not with the R-(-)-ibuprofen. The fluorescence intensity of the β-CD-QDs was linearly dependent on the concentration of the S-(+)-IBP in the range of 0-0.5 nmol/L with an limit of detection of 0.29 nmol/L.

Synthesis, Photophysical Characterization, and Sensor Activity of New 1,8-Naphthalimide Derivatives

Three new 1,8-naphthalimide derivatives M1-M3 with different substituents at the C-4 position have been synthesized and characterized. Their photophysical properties have been investigated in organic solvents of different polarity, and their fluorescence intensity was found to depend strongly on both the polarity of the solvents and the type of substituent at C-4. For compounds M1 and M2 having a tertiary amino group linked via an ethylene bridge to the chromophore system, high quantum yield was observed only in non-polar media, whereas for compound M3, the quantum efficiency did not depend on the medium polarity. The effect of different metal ions (Ag⁺, Ba²⁺, Cu²⁺, Co²⁺, Mg²⁺, Pb²⁺, Sr²⁺, Fe³⁺, and Sn²⁺) on the fluorescence emission of compounds M1 and M2 was investigated. A significant enhancement has been observed in the presence of Ag⁺, Pb²⁺, Sn²⁺, Co²⁺, Fe³⁺, as this effect is expressed more preferably in the case of M2. Both compounds have shown significant pH dependence, as the fluorescence intensity was low in alkaline medium and has been enhanced more than 20-fold in acidic medium. The metal ions and pH do not affect the fluorescence intensity of M3. Density-functional theory (DFT) and Time-dependent density-functional theory (TDDFT) quantum chemical calculations are employed in deciphering the intimate mechanism of sensor mechanism. The functional properties of M1 and M2 were compared with polyamidoamine (PAMAM) dendrimers of different generations modified with 1,8-naphthalimide.

Mixed alkoxy/hydroxy 1,8-naphthalimides: expanded fluorescence colour palette and in vitro bioactivity

An efficient and functional group tolerant route to access hydroxy 1,8-naphthalimides has been used to synthesise a range of mono- and disubstituted hydroxy-1,8-naphthalimides with fluorescence emissions covering the visible spectrum. The dialkoxy substituted compounds prepared possess high quantum yields (up to 0.95) and long fluorescent lifetimes (up to 14 ns). The method has been used to generate scriptaid analogues that successfully inhibit HDAC6 in vitro with tubulin acetylation assays confirming that these compounds are more effective than tubastatin.

A “weak acid and weak base” type fluorescent probe for sensing pH: mechanism and application in living cells

A simple pH fluorescent probe, N-(6-morpholino-1, 3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl) isonicotinamide (NDI), based on naphthalimide as the fluorophore and isonicotinic acid hydrazide as the reaction site was synthesized and characterized. It is useful for monitoring acidic and alkaline pH. The results of pH titration indicated that NDI exhibits obvious emission enhancement with a pK_a of 4.50 and linear response to small pH fluctuations within the acidic range of 3.00–6.50. Interestingly, NDI also displayed strong pH-dependent characteristics with pK_a 9.34 and linearly responded to an alkaline range of 8.30–10.50. The sensing response mechanism was confirmed by ¹H NMR and ESI-MS spectroscopy. The mechanism of the optical responses of NDI toward pH was also determined by density functional theory (DFT) calculations. In addition, NDI displayed a highly selective and sensitive response to hydrogen ions and hydroxyl ions. The probe was successfully applied to image acidic and alkaline pH value fluctuations in HeLa cells and has lysosomal targeting ability.

When the probe was in the protonation process, the fluorescence intensity gradually decreased, whereas when the probe was in the deprotonation process, the fluorescence intensity gradually increased.

Synthesis of a single 1,8-naphthalimide fluorophore as a molecular logic lab for simultaneously detecting of Fe3+, Hg2+ and Cu2

A novel fluorescence sensing 1,8-naphthalimide fluorophore is synthesized and investigated. The novel probe comprising two different binding moieties is capable to detect selectively Fe³⁺ over the other representative metal ions as well as a combination of biologically important cations such as Fe³⁺, Cu²⁺ and Hg²⁺ in the physiological range without an interfering effect of the pHs. Due to the remarkable fluorescence changes in the presence of Fe³⁺, Hg²⁺ and Cu²⁺ ions, INH and AND logic gates are executed and the system is able to act as a single output combinatorial logic circuit with three chemical inputs.

Synthesis, fluorescence-sensing and molecular logic of two water-soluble 1,8-naphthalimides

Two novel highly water-soluble fluorescence sensing 1,8-naphthalimides are synthesized and investigated. The novel compounds are designed on the "fluorophore-receptor₁-spacer-receptor₂" model as a molecular fluorescence probe for determination of cations and anions in 100% aqueous media. The novel probes comprising N-imide and N-phenylpiperazine or morpholine substituents are capable to operate simultaneously via ICT and PET signaling mechanism as a function of pH and to recognize selectively Cu²⁺ and Hg²⁺ over the other representative metal ions. Due to the remarkable fluorescence changes in the presence of protons, hydroxyl anions, Hg²⁺ and Cu²⁺, INH and doubly disabled INH logic gates are executed and the systems are able to act as a single output combinatorial logic circuit with four chemical inputs.

Novel nanosized water soluble fluorescent micelles with embedded perylene diimide fluorophores for potential biomedical applications: cell permeability, localization and cytotoxicity

Novel biocompatible water-soluble fluorescent micelles with embedded perylene diimides (PDI) for intracellular applications have been prepared by self assembling of amphiphilic poly(vinyl alcohol)-b-poly(acrylonitrile) (PVA-b-PAN) copolymers in the presence of synthesized fluorophores. Amphiphilic PVA-b-PAN copolymers were obtained by selective hydrolysis of well-defined poly(vinyl acetate)-b-poly(acrylonitrile) (PVAc-b-PAN) copolymer. The preparation of the novel fluorescence micelles consisting of PVA hydrophilic shell and PAN hydrophobic core with incorporated PDI fluorophores has been confirmed by DLS and TEM analysis. The cytotoxicity of the water-soluble fluorophores and their internalization into living cells depending on the micellar concentration have been tested. It was shown that they could successfully enter in living cells without destroying their morphology. The results obtained indicate that the novel water-soluble fluorescent micelles with embedded PDI fluorophores would be suitable for potential intracellular biomedical applications.

A highly selective ratiometric fluorescent pH probe based on a PAMAM wavelength-shifting bichromophoric system

A novel PAMAM wavelength-shifting bichromophoric system has been successfully developed. Novel compound was configured as a light harvesting antenna where the system surface is labeled with yellow-green emitting 4-(N,N-dimethylamino)ethylamino-1,8-naphthalimide "donor" units capable of absorbing light and efficiently transferring the energy to a focal Rhodamine 6G "acceptor". The periphery of the system was designed on the "fluorophore-spacer-receptor" format, capable of acting as a molecular fluorescence photoinduced electron transfer based probe. Due to the both effects, photoinduced electron transfer in the periphery of the system and pH dependent rhodamine core absorption, novel antenna is able to act as a selective ratiometric pH fluorescence probe in aqueous medium. Thus, the distinguishing features of the fluorescence resonance energy transfer systems were successfully combined with the properties of classical ring-opening charge transfer systems, which may be beneficially for monitoring pH variations in complex samples.

Synthesis and sensor activity of a PET-based 1,8-naphthalimide Probe for Zn(2+) and pH determination

A novel blue-emitting 1,8-naphthalimide fluorophore designed as a molecular PET-based probe for determination of pH and detection of transition metal ions in the environment was successfully synthesized. Novel compound was configured on the "fluorophore-spacer-receptor" format. Due to the tertiary amine receptor the novel system showed "off-on" switching properties under the transition from alkaline to acid media (FE = 3.2) and in the presence of Zn(2+) ions (FE = 2.5). The results obtained illustrate the high potential of the synthesized blue-emitting 1,8-naphthalimide fluorophore as an efficient pH chemosensing material and a selective probe for Zn(2+) ions.

A novel fluorescent pH probe with valuable pKabased on a twisted intramolecular charge transfer mechanism, and its applications in cell imaging

A novel TICT-mechanism based pH probe with valuable pK_aof 5.32 has been developed. It is a promising visualizing agent for lysosomes in intracellular application.