Dual Fluorescent N-Aryl-2,3- naphthalimides: Applications in Ratiometric DNA Detection and White Organic Light-Emitting Devices

Dual and Panchromatic Emission from N-Aryl-phenanthridinones: Extension of the Seesaw Photophysical Model with a Slight Twist

White-light emission from a single organic molecule, known as a single white-light emitter, is a rare phenomenon and desirable property for a class of materials with potential future applications in white lighting. Since N-aryl-naphthalimides (NANs) have been shown to follow excited state behavior and unique dual or panchromatic emission through a substituent pattern prescribed via a seesaw photophysical model, this study investigates the substituent effects on the fluorescence emission of structurally related N-aryl-phenanthridinones (NAPs) dyes. Following a similar placement prescription of an electron-releasing group (ERG) and electron-withdrawing group (EWG) at the phenanthridinone core and N-aryl moiety, we discovered from time-dependent density functional theory (TD-DFT) results that NAPs show a substitution pattern opposite to NANs in order to promote S2 and higher excited states. Interestingly, 2-methoxy-5-[4-nitro-3(trifluoromethyl)phenyl]phenanthridin-6(5H)-one 6e displayed a pronounced dual and panchromatic fluorescence dye depending on the solvent. For the six dyes included in the study, full spectral information in a variety of solvents, as well as fluorescence quantum yield and lifetime are reported. TD-DFT calculations support the predicted optical behavior via mixing of S2 and S6 excited states via anti-Kasha type of emission behavior.

Effect of solvent inclusion on the structures and solid-state fluorescence of coordination compounds of naphthalimide derivatives and metal halides

The structural characteristics and solid-state fluorescence of coordination compounds formed between the fluorophore N-((3-pyridyl)methyl)-1,8-naphthalimide (3-pn) and a range of divalent metal halides, were investigated. Six new crystal structures, of the formula ML 2 X 2.solv, were obtained through the combination of the organic ligand L = 3-pn with the divalent metal halides CoX2 (X = Cl− or Br−) or ZnX2 (X = Cl− or Br−) in different solvents. It was found that solvent molecules are incorporated into all the structures, and that the same complex can incorporate different solvent molecules. The conformation of the complex molecule is determined by the solvent molecule incorporated into the structure. The fluorescence intensity is affected by the identity of the metal and halido ligand in the complex molecule, while the identity of the solvent molecule and the metal ion affects the emission wavelength. Thus, the solvent of crystallisation impacts on the solid-state fluorescence of the compounds, hence the same complex can be made to fluoresce at different wavelengths depending on the solvent of crystallisation.

Unraveling the Mechanistic Pathway for the Dual Fluorescence in Green Fluorescent Protein (GFP) Chromophore Analogue: A Detailed Theoretical Investigation

The photophysical properties of the para-sulfonamide (p-TsABDI) analogue of the green fluorescent protein (GFP) chromophore with both proton donating and accepting sites have been exploited in polar solvents to understand the origin of the unusual dual fluorescence nature of the chromophore. In the polar solvents, the compound undergoes structural rearrangement upon photoexcitation, leading to the ultrafast excited-state intermolecular proton transfer (ESIPT) phenomenon at the S₁ surface. In this work, we employed both the static electronic structure calculations and on-the-fly molecular dynamics simulation to unravel the underlying reason for this peculiar behavior of the p-TsABDI analogue in polar solvents. To represent this adequately and provide extensive information on the ESIPT mechanism mediated by the solvent molecules, we considered explicit solvent molecules using the integral equation formalism variant of polarizable continuum (IEFPCM) model. From the static calculation analysis, we can conclude that the dual emissive behavior of the compound is ascribed to the proton transfer (PT) phenomena in the excited-state. However, based on the static calculation exclusively, it is hard to ascertain the mechanistic pathway of the PT phenomena. Hence, to investigate the dynamics and reaction mechanism for the ESIPT process, we performed the on-the-fly dynamics simulation for p-TsABDI in solvent clusters. Dynamics simulation results reveal that, based on the time lag between all the proton transfer processes, the ESIPT mechanism occurs in a stepwise manner from the benzylidene moiety of the chromophore to its imidazolinone moiety. However, the nonexistence of crossings between the S₁- and S₀-states confirms the PT characteristics of the reactions.

Progress in the Chemistry of Cytochalasans

Cytochalasans are a group of fungal-derived natural products characterized by a perhydro-isoindolone core fused with a macrocyclic ring, and they exhibit a high structural diversity and a broad spectrum of bioactivities. Cytochalasans have attracted significant attention from the chemical and pharmacological communities and have been reviewed previously from various perspectives in recent years. However, continued interest in the cytochalasans and the number of laboratory investigations on these compounds are both growing rapidly. This contribution provides a general overview of the isolation, structural determination, biological activities, biosynthesis, and total synthesis of cytochalasans. In total, 477 cytochalasans are covered, including "merocytochalasans" that arise by the dimerization or polymerization of one or more cytochalasan molecules with one or more other natural product units. This contribution provides a comprehensive treatment of the cytochalasans, and it is hoped that it may stimulate further work on these interesting natural products.

Practical access to fluorescent 2,3-naphthalimide derivatives via didehydro-Diels-Alder reaction

A practical and efficient approach for the synthesis of fluorescent 2,3-naphthalimide derivatives has been developed from readily available starting materials via an intramolecular didehydro-Diels-Alder reaction, which proceeded well under room temperature, exhibiting a wide substrate scope and good functional group tolerance. The practicability of this methodology has been verified by one-step synthesis of the environmentally sensitive fluorophore 6-DMN on a gram scale with a shorter time, fewer steps and less waste disposal, and without the utilization of toxic transition metals. The present experimental and computational studies support the crucial role of the propiolimide moiety in the transformation.

Coexistence of structurally similar but electronically distinct isomers of delocalized cation radicals as a basis for the development of functional materials

Certain low-symmetry aromatic molecules with a small HOMO/HOMO-1 energy gap might co-exist as electronic isomers in their cation radical states that differ only in bond lengths yet have distinct optical and electronic properties. These electronic isomers are sensitive to the environment and might be used for the development of novel functional materials.

A coumarin–hemicyanine hybrid as a ratiometric fluorescent sensor of microenvironment proticity

ICT-based ratiometric fluorescent probe developed to selectively monitor microenvironment proticity within biopolymer targets with well resolved dual emission channels.

Aggregation-Induced Emission and White Luminescence from a Combination of π-Conjugated Donor-Acceptor Organic Luminogens

Two new star-shaped phenyl- and triazine-core based donor-acceptor (D-A) type conjugated molecules bearing triphenylamine end-capped arms were synthesized and characterized as imminent organic optoelectronic materials. Photophysical properties of the compounds were explored systematically via spectroscopic and theoretical methods. Because of the presence of donor-acceptor interactions, these luminogens display multifunctional properties, for instance, high extinction coefficient, large stokes shift, and pronounced solvatochromic effect. The compounds also exhibited phenomenon known as aggregation-induced emission on formation of nano-aggregates in the tetrahydrofuran-water mixture. The aggregate formation was confirmed by transmission electron microscopy, scanning electron microscopy, and dynamic light scattering analyses. Moreover, by controlling the electron withdrawing ability of the acceptor, complementary emissive fluorophores (blue and yellow) were achieved. These two complementary colors together span the entire range of visible spectrum (400-800 nm) and therefore when mixed in a requisite proportion generate white light in solution phase. These findings have potential for the progress of new organic white light radiating materials for applications in lighting and display devices.

Phthalimide Derivatives with Bioactivity against Plasmodium falciparum: Synthesis, Evaluation, and Computational Studies Involving bc 1 Cytochrome Inhibition

We describe herein the design and synthesis of N-phenyl phthalimide derivatives with inhibitory activities against Plasmodium falciparum (sensitive and resistant strains) in the low micromolar range and noticeable selectivity indices against human cells. The best inhibitor, 4-amino-2-(4-methoxyphenyl)isoindoline-1,3-dione (10), showed a slow-acting mechanism similar to that of atovaquone. Enzymatic assay indicated that 10 inhibited P. falciparum cytochrome bc ₁ complex. Molecular docking studies suggested the binding mode of the best hit to Qo site of the cytochrome bc ₁ complex. Our findings suggest that 10 is a promising candidate for hit-to-lead development.

Intense White Molecular Fluorescence from Naphthoxazole-Quinoline Derivatives

Naphthoxazole derivatives are small heterocyclic compounds endowed with outstanding fluorescence properties. In this work, we report a detailed study of the intense white light fluorescence observed in naphthoxazole-quinoline dyads in solvent mixtures including at least a strong hydrogen bonding solvent. The same phenomenon was also studied in inclusion complexes naphthoxazole derivatives-sulfonated-βCD either in aqueous solution as well as in solid phase. A novel mechanism of white molecular fluorescence generation based on solvent-to-fluorophore proton transfer facilitated by ground state hydrogen bonding was characterized. The emission combines both, a blue charge transfer fluorescence emitted by the locally excited singlet state along with a red-shifted emission from a proton transfer complex.

Design of "Click" Fluorescent Labeled 2'-deoxyuridines via C5-[4-(2-Propynyl(methyl)amino)]phenyl Acetylene as a Universal Linker: Synthesis, Photophysical Properties, and Interaction with BSA

Microenvironment-sensitive fluorescent nucleosides present attractive advantages over single-emitting dyes for sensing inter-biomolecular interactions involving DNA. Herein, we report the rational design and synthesis of triazolyl push-pull fluorophore-labeled uridines via the intermediacy of C5-[4-(2-propynyl(methyl)amino)]phenyl acetylene as a universal linker. The synthesized nucleosides showed interesting solvatochromic characteristic and/or intramolecular charge transfer (ICT) features. A few of them also exhibited dual-emitting characteristics evidencing our designing concept. The HOMO-LUMO distribution showed that the emissive states of these nucleosides were characterized with more significant electron redistribution between the C5-[4-(2-propynyl(methyl)amino)]phenyl triazolyl donor moiety and the aromatic chromophores linked to it, leading to modulated emission property. The solvent polarity sensitivity of these nucleosides was also tested. The synthesized triazolyl benzonitrile (10C), naphthyl (10E), and pyrenyl (10G) nucleosides were found to exhibit interesting ICT and dual (LE/ICT) emission properties. The dual-emitting pyrenyl nucleoside maintained a good ratiometric response in the BSA protein microenvironment, enabling the switch-on ratiometric sensing of BSA as the only protein biomolecule. Thus, it is expected that the new fluorescent nucleoside analogues would be useful in designing DNA probes for nucleic acid analysis or studying DNA-protein interactions via a drastic change in fluorescence response due to a change in micropolarity.

Spectroscopic investigation of bio-mimetic solvolysis of 6-(N,N-dimethylamino)-2,3-naphthalic anhydride in confined nanocavities

Enzymes are biological catalysts that can vastly accelerate the reaction rate of a substrate by accommodating it within the active site.

Investigation of a sensing approach based on a rapid reduction of azide to selectively measure bioavailability of H2S

A new reaction-based sensor (AHS) was synthesized for quantitative detection of H2S. AHS showed a high selectivity and sensitivity toward H2S over other thio-containing molecules, or reducing reagents with high abundance in living cells. In the presence of H2S, significant fluorescence enhancement (17-fold) was observed due to the reduction of the azide on AHS. The absorption (362 nm) and fluorescence emission (557 nm) of reduced AHS showed a highly linear correlation to H2S level, which were used to measure concentration of H2S in the range of 0-100 μM.

Ratiometric mechanosensitive fluorescent dyes: Design and applications

Fluorescent molecules, with their almost instantaneous response to external influences and relatively low-cost measurement instrumentation, have been attractive analytical tools and biosensors for centuries. More recently, advanced chemical synthesis and targeted design have accelerated the development of fluorescent probes. This article focuses on dyes with segmental mobility (known as fluorescent molecular rotors) that act as mechanosensors, which are known for their relationship of emission quantum yield with microviscosity. Fluorescence lifetime is directly related to quantum yield, but steady-state emission intensity is not. To remove confounding factors with steady-state instrumentation, dual-band emission dyes can be used, and molecular rotors have been developed that either have intrinsic dual emission or that have a non-sensitive reference unit to provide a calibration emission band. We report on theory, chemical structure, applications and targeted design of several classes of dual-emission molecular rotors.

Tuning the reaction rates of fluoride probes for detection in aqueous solution

Tuning the reaction rates of fluoride probes for detection in aqueous solution by varying the pendent groups of probe molecules.

Solvent-induced multicolour fluorescence of amino-substituted 2,3-naphthalimides studied by fluorescence and transient absorption measurements

Amino-substituted 2,3-naphthalimide derivatives showed marked positive solvatofluorochromism, and the fluorescence emission was effectively quenched in methanol via the internal conversion process.

White light emissive molecular siblings

White-light emission from boron based molecular siblings.

A ratiometric fluorescent probe for detection of biogenic primary amines with nanomolar sensitivity

An ultrasensitive ratiometric fluorescent sensor made of an N,N-dimethylaminonaphthalene anhydride moiety for detection of aliphatic primary amines is reported.

Cascade DNA logic device programmed ratiometric DNA analysis and logic devices based on a fluorescent dual-signal probe of a G-quadruplex DNAzyme

Two fluorescence sensitive substrates of G4 DNAzyme with inverse responses were simultaneously used to a cascade advanced DNA logic device based DNA analysis for the first time.

Discovery of potent indenoisoquinoline topoisomerase I poisons lacking the 3-nitro toxicophore

3-Nitroindenoisoquinoline human topoisomerase IB (Top1) poisons have potent antiproliferative effects on cancer cells. The undesirable nitro toxicophore could hypothetically be replaced by other functional groups that would retain the desired biological activities and minimize potential safety risks. Eleven series of indenoisoquinolines bearing 3-nitro bioisosteres were synthesized. The molecules were evaluated in the Top1-mediated DNA cleavage assay and in the National Cancer Institute's 60 cell line cytotoxicity assay. The data reveal that fluorine and chlorine may substitute for the 3-nitro group with minimal loss of Top1 poisoning activity. The new information gained from these efforts can be used to design novel indenoisoquinolines with improved safety.

An abiotic fluorescent probe for cardiac troponin I

The first ratiometric fluorescent reporter was designed for the detection of cardiac troponin I (cTnI), a key protein elicited during cardiac muscle cell death. In designing this abiotic fluorescent probe, docking simulation studies were performed to predict the probe/protein interactions along the solvent exposed regions of cTnI. Simple cuvette titration experiments in aqueous buffered solution indicate remarkable selectivity for cardiac troponin in the clinically relevant nM region versus skeletal troponin.