Naphthalene Chromophores Research Articles

Ion sensing with a calix[4]arene bifunctional receptor with thiosemicarbazone moieties and naphthalene chromophore

Ion sensing with a calix[4]arene bifunctional receptor with thiosemicarbazone moieties and naphthalene chromophore

Harmonizing Topological Features of Self-Assembled Fibers by Rosette-Mediated Random Supramolecular Copolymerization and Self-Sorting of Monomers by Photo-Cross-Linking.

Random copolymerization is an effective approach to synthesize the desired polymers by harmonizing distinct properties of different monomers. For supramolecular polymers in which monomer binding is inherently dynamic, it is difficult to achieve random copolymerization of monomers with distinct molecular structures and properties due to an enthalpic advantage upon self-recognition (self-sorting). Herein, we demonstrate an example of thermodynamically controlled random supramolecular copolymerization of two monomers functionalized with barbituric acid via the formation of six-membered hydrogen-bonded rosette intermediates to exhibit structural harmonization of the two main-chain motifs, i.e., intrinsically curved and linear motifs. One monomer based on naphthalene chromophore exclusively forms toroidal fibers, whereas another one bearing additional photoreactive diacetylene moiety affords linearly elongated fibers. Supramolecular copolymerization of the two monomers is achieved by cooling hot monomer mixtures in a nonpolar solvent, which results in the formation of thermodynamically stable spirally folded yet elongated fibers. Atomic force microscopic observations and theoretical simulations of the experimental data obtained by absorption spectroscopy reveal the homopolymerization of the diacetylene-functionalized monomer in the high-temperature region, followed by the incorporation of the naphthalene monomer in the medium-temperature region to form supramolecular copolymers with random monomer sequence. Finally, we demonstrate that the random copolymerization process can be switched to a narcissistically self-sorting one by deactivating monomer exchange through the photo-cross-linking of the diacetylene-functionalized monomers.

NIR-Responsive Lysosomotropic Phototrigger: An "AIE + ESIPT" Active Naphthalene-Based Single-Component Photoresponsive Nanocarrier with Two-Photon Uncaging and Real-Time Monitoring Ability.

In recent times, organelle-targeted drug delivery systems have gained tremendous attention due to the site-specific delivery of active drug molecules, resulting in enhanced bioefficacy. In this context, a phototriggered drug delivery system (DDS) for releasing an active molecule is superior, as it provides spatial and temporal control over the release. So far, a near-infrared (NIR) light-responsive organelle-targeted DDS has not yet been developed. Hence, we introduced a two-photon NIR light-responsive lysosome-targeted "AIE + ESIPT" active single-component DDS based on the naphthalene chromophore. The two-photon absorption cross section of our DDS is 142 GM at 850 nm. The DDS was converted into pure organic nanoparticles for biological applications. Our nano-DDS is capable of selective targeting, AIE luminogenic imaging, and drug release within the lysosome. In vitro studies using cancerous cell lines showed that our single-component photoresponsive nanocarrier exhibited enhanced cytotoxicity and real-time monitoring ability of drug release.

Green fluorescent waterborne polyurethane polyols

In this paper, we reported a series of green fluorescent flame-retardant waterborne polyurethane polyols. The polyurethane polyols were uniformly sized and possessed decent colloidal stability. Comparing to other reported products, our aqueous dispersions showed much stronger fluorescence intensity and greatly improved long-term stability, which were desired for practical applications. Small molecule conjugation units were gated into polyurethane chains via reaction between −OH of naphthalene and −NCO of diisocyanate, which restricts intramolecular rotation of naphthalene chromophores and non-radiative transition to enhance fluorescence intensity. The non-radiative transition and chromophore aggregation are weakened to hinder aggregation-caused quenching of chromophores to improve fluorescence by weak collision. This study has demonstrated a facile method to prepare waterborne polyurethane polyols, providing detailed explanation and guidance for related work in the future.

Induced axial chirality by a tight belt: naphthalene chromophores fixed in a 2,5-substituted cofacial para-phenylene-ethynylene framework.

We report the design of a synthetically easy accessible axial chirality-inducing framework for a chromophore of choice. The scaffold consists of two basic para-phenylene-ethynylene backbones separated by laterally placed corner units. Substitution with an inherently achiral chromophore at the 2 and 5 positions of the central phenylene excitonically couples the chromophore associated transition and thereby results in chiroptical properties. Using 6-methoxynaphthalene as a model chromophore, we present the synthesis, structural analysis and spectroscopic investigation of the framework. The chiral framework was synthesized in three straightforward synthetic steps and fully characterized. The obtained racemic compounds were resolved using HPLC and assignment of the absolute configuration was performed using the exciton chirality method, crystallography and DFT calculations. This simple yet potent framework might prove useful to enrich the structural diversity of chiral materials.

Synthesis, Characterization, and Photophysics of Self-Assembled Mn(II)-MOF with Naphthalene Chromophore

The unique and highly organized three-dimensional structure of metal–organic frameworks (MOFs) formed by self-assembled organic chromophores with metal ions emerges as next-generation luminophores ...

Point-to-Axial Chirality Transmission: A Highly Sensitive Triaryl Chirality Probe for Stereochemical Assignments of Amines.

A readily available stereodynamic and the electronic circular dichroism (ECD)-silent 2,5-di(1-naphthyl)-terephthalaldehyde-based probe has been applied for chirality sensing of primary amines. The chiral amine (the inductor) forces a change in the structure of the chromophore system through the point-to-axial chirality transmission mechanism. As a result, efficient induction of optical activity in the chromophoric system is observed. The butterflylike structure of the probe, with the terminal aryl groups acting as changeable “wings”, allowed for the generation of exciton Cotton effects in the region of 1Bb electronic transition in the naphthalene chromophores. The sign of the exciton couplets observed for inductor–reporter systems might be correlated with an absolute configuration of the inductor, whereas the linear relationship between amplitudes of the specific Cotton effect and enantiomeric excess of the parent amine gives potentiality for quantitative chirality sensing. Despite the structural simplicity, the probe turned out to be unprecedentedly highly sensitive to even subtle differences in the inductor structure (i.e., O vs CH2).

Experimental and DFT Study of the Photoluminescent Green Emission Band of Halogenated (-F, -Cl, and -Br) Imines.

The morphological, optical, and structural changes in crystalline chiral imines derived from 2-naphthaldehyde as a result of changing the −F, −Cl, and −Br halogen (−X) atoms are reported. Scanning electron microscopy (SEM), optical absorption, photoluminescence (PL), and powder X-ray diffraction (XRD) studies were performed. Theoretical results of optical and structural properties were calculated using the PBE1PBE hybrid functional and compared with the experimental results. Differences in surface morphology, absorbance, XRD, and PL of crystals were due to the change of halogen atoms in the chiral moiety of the imine. Absorption spectra exhibited the typical bands of the naphthalene chromophore located in the ~200–350 nm range. Observed absorption bands in the UV region are associated with π→π* and n→π* electronic transitions. The band gap energy was calculated using the Tauc model. It showed a shift in the ~3.5–4.5 eV range and the crystals exhibited different electronic transitions associated with the results of absorbance in the UV region. XRD showed the monoclinic→orthorhombic crystalline phase transition. PL spectra displayed broad bands in the visible region and all the samples have an emission band (identified as a green emission band) in the ~400–750 nm range. This was associated with defects produced in the morphology, molecular packing, inductive effect and polarizability, crystalline phase transition, and increase in size of the corresponding halogen atoms; i.e., changes presumably induced by −C−X…X−, −C−X…N−, −C−N…π, and −C−X…π interactions in these crystalline materials were associated with morphological, optical, and structural changes.

Photophysical Impact of Diacetylenic Conjugation on Classical Donor-Acceptor Electronic Energy Pair.

Organic fluorophores with extended π-conjugation are important for their widespread applications. The present work provides photophysical insights into a diacetylene bridged classical donor-acceptor electronic energy pair, naphthalene-pyrene, in comparison with its constituents' molecular structures, naphthyl and pyrenyl acetylenes, as well as parent naphthalene and pyrene chromophores. The diacetylenic dye loses the individual spectral identities of the donor and acceptor fluorophores exhibiting a locally excited (LE) emission (∼411 nm) from the overall molecular entity with high fluorescence quantum yields (0.55-0.84) in nonaqueous media. In contrast to the parent pyrene, the hybrid derivative shows a strongly allowed S0 → S1 transition. In mixed-aqueous media, the dye forms aggregates displaying a new red-shifted absorption (∼425 nm) as well as emission (∼510 nm) band. Unlike the hybrid dye, the naphthyl and pyrenyl acetylenes do not form aggregates. In the aggregate state of the hybrid fluorophore, electronic energy transfer takes place from the naphthyl moiety to pyrenyl ring. The excited-state photophysical properties of the dye are exploited in vapor sensing in the solid state.

Luminescent Supramolecular Heterometallic Macrocycles and their Encapsulation on Cholate Gels

The metal complex formed by coordination of ZnII to 1,7‐bis(4‐methylpyridine)‐4‐(2‐naphthylmethyl)‐1,4,7‐triazaheptane (ZnL2+) was reacted in aqueous solution with [Pd(NO3)2(en)] and [Pt(NO3)2(en)] salts to form the self‐assembled heterometallic macrocycles [Zn2L2Pd2(en)2]8+ and [Zn2L2Pt2(en)2]8+, respectively. PdII and PtII‐coordination modulates the original emission of ZnL2+ arising from the presence of the naphthalene chromophore and the formation of the macrocycles can be monitored due to the PET process occurring with coordination of PdII and PtII to the pyridine units of ZnL2+. Additionally, several studies reveal that these heteromacrocycles can be encapsulated in ZnII‐cholate hydrogels giving rise to soft materials with tunable emissive properties. Preliminary analysis show also that the addition of the metallic species in micromole concentration to the cholate hydrogels resulted in an improved mechanical strength of the final materials.

Intramolecular energy transfer and photoisomerization in stilbene dendrimers

Stilbene dendrimers with energy harvesting chromophores, such as naphthalene and benzophenone, have been prepared and their photochemical and photophysical properties have been examined. These dendrimers underwent trans–cis mutual photoisomerization on excitation of the core stilbene or the peripheral naphthalene and benzophenone chromophores through several energy transfer processes, and photophysical processes such as intersystem crossing finally resulted in cis-trans isomerization of the core stilbene.

Optical, thermal and combustion properties of self-colored polyamide nanocomposites reinforced with azo dye surface modified ZnO nanoparticles

New self-colored aromatic-polyamide (PA) nanocomposites containing azo and naphthalene chromophores were prepared with azo-dye surface-modified ZnO nanoparticles (SMZnO) using solution method in dimethylformamide. The X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results showed the uniform distribution for ZnO nanoparticles in the PA matrix. The UV–vis spectra of PA/ZnO nanocomposites (PANC) showed a blue shift as well as reduction in absorbance intensities and the photoluminescence studies revealed that the increasing intensities of the violet emission in SMZnO loading. From thermo gravimetric analysis (TGA), the temperature at 10% mass loss (T10) increased from 291.8°C to 387.6°C for PANC containing 8 mass% of SMZnO, as well as the char yield enhanced significantly, which was about 23.5% higher than the neat PA. The peak heat release rate resulted from microscale combustion calorimeter (MCC), by 8 mass% loading of SMZnO, decreased about 56.9% lower than the neat PA.

A pH‐Gated Photocage

Orthogonal control can be imposed on the photocleavage of a dioxinone heterocycle with the introduction of an amino substituent. Photoinduced electron transfer from this group to a naphthalene chromophore quenches the excited state responsible for the photochemical reaction. Protonation of the amino group prevents electron transfer and allows the cleavage of the dioxinone ring into a hydroxyester and a ketone.

A ratiometric fluorescent formaldehyde probe for bioimaging applications.

We have described a ratiometric fluorescent formaldehyde probe (RFFP) based on the 6-hydroxy naphthalene chromophore for the first time. The probe is suitable for ratiometric detection of formaldehyde both in the solution and living biological samples with two distinct emission bands.

Photophysical Studies on Covalently-linked Naphthalene and TEMPO Free Radical Systems: Observation of a Charge Transfer State in the Ground State.

A series of molecules containing a naphthalene chromophore and a stable free radical 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) covalently linked by a spacer group of different lengths have been synthesized. In n-hexane solution, their photophysical behavior was studied and compared with a system of freely moving naphthalene and the free radical TEMPO. The linked molecules showed strong quenching of the singlet and triplet states of the naphthalene moiety, compared to when naphthalene and TEMPO were not linked. The quenching efficiency decreased with increasing the length of the spacer group. In addition, new electronic absorption and emission bands, along with the usual bands of the individual moieties, were also seen. These news bands have been attributed to the formation of electron donor-acceptor charge-transfer complexes in the ground state, arising from the interaction between the two moieties in close proximity. The photophysical dynamics of the linked molecules has been rationalized by assuming the existence of two types of population of the linked molecules: folded and extended. The ground state complex formation is proposed to occur only in the folded conformation of the linked molecules. To our knowledge, this is possibly the first example of a ground state charge-transfer complex formation involving a TEMPO free radical and naphthalene.

Configuration-Dependent Photoinduced Electron Transfer in Diastereomeric Naphthalene-Amino-Naphthalene Triads.

Novel diastereomeric triads containing two naphthalene chromophores have been designed in which an electron-donating amine moiety is covalently integrated into the connecting bridge. Photophysical studies (steady-state and time-resolved fluorescence) in solvents of different polarity have been performed. A remarkable stereodifferentiation in the intramolecular fluorescence quenching was found in acetonitrile. Laser flash photolysis gave rise to naphthalene-derived radical cations, which were also quenched by the amine with an even higher degree of stereodifferentiation. The results are in agreement with thermodynamic estimations and indicate that photoinduced electron transfer (PET) is the main quenching pathway. Furthermore, theoretical calculations have allowed us to explain the experimentally observed stereodifferentiation in PET quenching.

Twisted baskets.

A preparative procedure for obtaining a pair of twisted molecular baskets, each comprising a chiral framework with either right ((P)-1syn) or left ((M)-1syn) sense of twist and six ester groups at the rim has been developed and optimized. The racemic (P/M)-1syn can be obtained in three synthetic steps from accessible starting materials. The resolution of (P/M)-1syn is accomplished by its transesterification with (1R,2S,5R)-(-)-menthol in the presence of a Ti(IV) catalyst to give diastereomeric 8(P) and 8(M). It was found that dendritic-like cavitands 8(P) and 8(M), in CD2Cl2, undergo self-inclusion ((1)H NMR spectroscopy) with a menthol moiety occupying the cavity of each host. Importantly, the degree of inclusion of the menthol group was ((1)H NMR spectroscopy) found to be greater in the case of 8(P) than 8(M). Accordingly, it is suggested that different folding characteristic of 8(P) and 8(M) ought to affect the physicochemical characteristics of the hosts to permit their effective separation by column chromatography. The absolute configuration of 8(P)/8(M), encompassing right- and left-handed "cups", was determined with the exciton chirality method and also verified in silico (DFT: B3LYP/TZVP). Finally, the twisted baskets are strongly fluorescent due to three naphthalene chromophores, having a high fluorescence quantum yield within the rigid framework of 8(P)/8(M).

Spectroscopic, Conductivity and Molecular Modeling Studies of the Inclusion Complex of TNDAB with Cucurbit[7]uril in Aqueous Solution

Abstract In this investigation, a novel surfactant (N, N, N-trimethyl-4-(5-decyloxy naphthalene-1-yloxy) butan-1-aminium bromide, TNDAB) with a naphthalene chromophore moiety was synthesized. The UV, fluorescence, conductivity measurements and molecular modeling have been carried out at 298 K for TNDAB + H2O, and TNDAB + CB[7] + H2O systems. The apparent critical micelle concentrations, the dissociation degree of the micelle, the hydrophobic contribution of the transfer free energy for the hydrocarbon chain of TNDAB, and the stoichoimetry, stability constant, and potential energy surface for the inclusion complex of TNDAB and CB[7] have been determined. The results suggested that CB[7] formed strong complex with TNDAB, the stoichoimetry of CB[7] and TNDAB was found to be almost 1:1, and hydrophobic interactions between the naphthalene nucleus of TNDAB and the cavity of the CB[7] are suggested to be the main driving forces in the association process. It also indicated that the naphthalene chromophore introduced can be as a spectral probe to examine the inclusion behaviors between host and guest molecules.

Synthetic control of isolated, single functional groups on silica surfaces.

We report control of the density of isolated, single functional groups in homogeneously mixed trichloroalkyl silanes on various silica surfaces. The functional groups are covalently bound to a silane derived from the Rink resin. This Rink-silane is reactive to any nucleophile. Control over the density of functional groups is achieved by diluting the immersion solution containing the Rink-silane with an inert silane, octadecyltrichlorsilane. The isolated nature of the functional groups is confirmed by the stochastic blinking of fluorescent single boron-dipyrromethane dyes imaged in total internal reflection geometry. The robust character of silane monolayers allows facile covalent binding and cleavage of molecular species from silica surfaces as well as general synthetic transformations to be conducted. This is shown by the covalent attachment and then cleavage of a naphthalene chromophore. This low-cost and scalable platform has great potential for use in sensing, molecular electronics, semiconductor processing, and the investigation of fundamental processes in catalysis and the kinetics of molecular association.

Photoactive graft amphiphilic polyelectrolyte: Facile synthesis, intramolecular aggregation and photosensitizing activity

Simple and versatile two-step procedure for synthesis of graft amphiphilic polyelectrolytes has been developed. A photoactive copolymer of poly(vinylnaphthalene) grafted from poly(sodium 2-acrylamido-2-methyl-1-propanesulfonate) (PAMPS-graft-PVN) was obtained and characterized. By separating the processes of generation of grafting sites on the precursor main chain and subsequent nitroxide-mediated polymerization (NMP), the formation of the unwanted homopolymer could be avoided. Combination of charged polymer backbone with short hydrophobic side chains in PAMPS-graft-PVN leads to spontaneous intramolecular aggregation of the macromolecule in an aqueous solution with formation of hydrophobic domains consisting of highly packed naphthalene chromophores arranged in a “pearl-necklace” structure as shown using atomic force microscopy. The presence of fluorophores in the polymer structure is beneficial for the studies of such macromolecular system as it allows application of emission spectroscopy, which is very sensitive to structural arrangement of the fluorophores. The domains formed within the polymer chain in an aqueous solution were also characterized using fluorescent molecular probes. Studies on photophysical properties of PAMPS-graft-PVN indicated that the polymer can be an efficient photosensitizer in photoinduced electron transfer processes. The proposed here synthetic approach can be easily applied for syntheses of other graft copolymers that are otherwise difficult to be obtained.