Fluorescent molecular sensory system based on bis pyrene-modified gamma-cyclodextrin dimer for steroids and endocrine disruptors.

A gamma-cyclodextrin dimer modified with two pyrene moieties, 6-(2-pyrenebutylate-aminoethyl)pyrenebutylate-amino-6-deoxy-bis-gamma-cyclodextrin, has been synthesized in the presence of N,N'-dicyclohexycarbodiimide from gamma-cyciodextrin dimer linked with ethylenediamine at an upper rim. The sensing ability and binding property of the titled dimer were investigated for bile acids and endocrine disruptors. This cyclodextrin dimer showed both monomer and excimer fluorescence; the guest-induced emissions were observed as increases or decreases depending on the guest. The values deltaI(m)/I0(m) and deltaI(ex)/I0(ex), where I0(m) and I(m) are fluorescence intensities of monomer emission in the absence and presence of a guest and I0(ex) and I(ex) are those of excimer emission and deltaI(m) and deltaI(ex) were I(m) - I0(m) and I(ex) - I0(ex), respectively, were used as a parameter of sensitivity. This host exhibited highly sensitive molecular recognition ability for bile acids and endocrine disruptors, in which the sensing parameters obtained from monomer emission were plus or minus values, whereas the parameters obtained as excimer emission were minus ones. The behavior of the appended moieties of the host during a host-guest complexation was studied by induced circular dichroism (ICD) and fluorescence spectra. The ICD intensities of the titled dimer were decreased upon an addition of a guest. The guest-induced variations in the fluorescence and ICD intensity suggest that the appended moieties move by altering the spatial relationship in the hydrophobic space between two linked cyclodextrins.     

Photophysics of a polyether containing tetramethylanthracene units

PESA is a rigid rod polymer incorporating anthrylene units in its backbone. The photophysics of PESA in solution are representative of the isolated anthracene chromophore. In the solid state, strong interchain excimer emission is observed. Solid PESA undergoes efficient photocrosslinking which we assign to interchain anthracene dimer formation. Competitive quenching of photocrosslinking by diphenyliodonium hexafluorophosphate suggests that localized singlet excitation energy can migrate among chains until trapped by excimer formation. The excimer state is intermediate in photocrosslinking. © 1993 John Wiley & Sons, Inc.     

Intramolecular excimer formation for covalently linked boron dipyrromethene dyes

Photophysical properties have been recorded for a small series of covalently linked, symmetrical dimers formed around boron dipyrromethene (Bodipy) dyes. Within the series, a control dimer is unable to adopt a cofacial arrangement because of steric factors, while a second dimer possesses sufficient internal flexibility to form the cofacial geometry but with little overlap of the Bodipy units. The other three members of the series take up a cofacial arrangement with varying bite angles between the planes of the two Bodipy units. Fluorescence quantum yields and excited-state lifetimes indicate differing extents of electronic interaction between the two Bodipy head-groups, but only the compound with the smallest bite angle exhibits excimer emission in solution under ambient conditions. Time-resolved fluorescence studies show dual-exponential decay kinetics in each case, while temperature-dependent emission studies reveal reversible coupling between monomer and lower-energy excimer states. The latter is weakly fluorescent, at best, and is seen clearly only for dimers having small bite angles. The application of high pressure to dilute solutions of these dimers promotes excimer formation in certain cases and leads to loss of monomer-like fluorescence. Under high pressure, excimer emission is more evident, and the overall results can be discussed in terms of subtle structural rearrangements that favor excimer formation.     

Solvent-driven multiply configurable on/off fluorescent indicator of the pH window: a diethylenetriamine bearing two end pyrene fragments

Fluorescence behaviors of a simple-structured molecule (L), a diethylenetriamine bearing two end pyrene fragments, have been investigated in water. Effects of adding a less-polar organic solvent (acetonitrile: MeCN) on the emission behaviors have been studied by means of steady-state and time-resolved fluorescence measurements. L dissolved in water shows dual-mode fluorescence consisting of monomer and excimer emissions. The monomer emission shows an "on-off" intensity profile against the pH window (pH 2-12), whereas the excimer emission shows an "off-on" profile. Upon MeCN addition, the monomer emission maintains the "on-off" profile. In contrast, the "off-on" profile of the excimer emission is drastically changed: L shows two more types of profiles, "off-on-off-on" and "off-on-off", along with the MeCN concentration increase, thus behaving as a multiply configurable fluorescent indicator of the pH window. The MeCN-driven excimer emission switching of L is triggered by (i) the decrease in stability of the intramolecular ground-state dimer (GSD) formed between the end pyrene fragments, which suppresses the direct photoexcitation of GSD (suppression of the "static" excimer formation), leading to a decrease in the excimer emission intensity at basic pH; and (ii) the decrease in polarity of solution, which allows formation of a "dynamic" excimer via a monomer-to-excimer transition, resulting in an enhancement of the excimer emission intensity at acidic-neutral pH.     

Normal and second excimers in macromolecules—I: Poly(1-methoxy-4-vinylnaphthalene) in fluid solution

The emission properties of poly(1-methoxy-4-vinylnaphthalene) (PMVN) in 2-methyltetrahydrofuran solution have been investigated over the range 77–350 K. It exhibits, in addition to the monomer fluorescence (348 and 360 nm), two structureless emissions derived from two different types of excimer, viz. the normal excimer (420 nm) and the second excimer (380 nm), the latter having a partially overlapping structure of aromatic rings. The intensity of second excimer emission of PMVN increases with decreasing temperature, while the normal excimer emission shows a maximum at 215 K. Kinetic analysis of transient decay curves for the fluorescence of PMVN gave results consistent with the previously reported kinetic scheme for the dimer model, 1,3-bis(4-methoxy-1-naphthyl)propane, showing that the second excimer is not formed from or converted to the normal excimer and that two types of excimer are formed independently from the excited monomer.     

A fluoride-selective PCT chemosensor based on formation of a static pyrene excimer

[reaction: see text] Calixarene-based fluorescent chemosensor 1 with two fluorogenic pyrene units conjugated to amide groups as guest recognition sites is synthesized. Complexation of F(-) by 1 causes a red shift of its absorption band to 400 nm (Deltalambda = 54 nm) and a blue shift of the excimer emission to 470 nm (Deltalambda = 12 nm) together with enhanced fluorescence intensity. The blue-shifted excimer emission is attributed to a pyrene dimer formed in the ground state, a so-called static excimer.     

Artificial Iono‐ and Photosensitive Membranes Based on an Amphiphilic Aza‐Crown‐Substituted Hemicyanine

Artificial iono‐ and photosensitive membranes based on an amphiphilic aza‐crown‐substituted hemicyanine are assembled on liquid and solid supports and their aggregation behaviour, which is influenced by the binding of metal cations and surface density, is studied. The photoinduced charge‐transfer properties of an analogous non‐amphiphilic hemicyanine in solution are also demonstrated. An asymmetric sandwich dimer model is proposed and existence of such dimers in solution is evidenced by transient absorption and fluorescence anisotropy experiments. Changes in absorption and emission spectra, as well as compression isotherms of the amphiphile observed in the presence of cations, are discussed in terms of 2D molecular reorganisation. Surface‐pressure‐controlled reversible excimer formation at the air–water interphase and excimer‐type emission of Langmuir–Blodgett films in the presence of cations are demonstrated and are discussed on the basis of fibre‐optic fluorimetry and fluorescence microscopy results.     

Alternately π-Stacked Systems Assisted by o-Carborane: Dual Excimer Emission and Color Modulation by Bcage-Methylation

Herein, we report the unique solid-state excimer emission of three types of acridine-tethered o-carboranes with variable degrees of methylation at the o-carborane unit. They all showed columnar packing structures based on dimer formation, and two types of π-overlapping motifs were alternately stacked. From the photoluminescence (PL) measurements on the crystalline samples, it was found that three types of luminescence bands can simultaneously appear: monomer emission, excimer emission from the moderately π-stacked intra-dimer unit, and excimer emission from the widely π-stacked inter-dimer unit. Consequently, the PL colors were drastically changed by the steric effect of the methyl groups, with a strong correlation found between the π-overlapping and excimer character. In addition, variable-temperature PL measurements revealed that these PL species should be in thermal equilibrium at room temperature, with the intensity ratios sensitive toward temperature changes.     

Observation of the diffusion-free intermolecular excimer of 9-methyladenine in aqueous solution by picosecond time-resolved spectroscopy

Diffusion-free intermolecular excimer formation in liquid solution is observed for an aqueous solution of 9-methyladenine using the synchroscan streak camera technique. The excimer fluorescence (330 ps lifetime) appears at 380 nm, at longer wavelength than the monomer fluorescence (5 ps lifetime). The excimer is formed via a weakly coupled stacking dimer composed of ground-state monomers.     

PHOTOPHYSICS and PHOTOCHEMISTRY OF BIS-2-(9-ANTHRYL)ETHYL GLUTARATE

Abstract— The photochemistry and photophysics of bis-(2-(9-anthryl)ethyl glutarate 2 and 2-(9-anthryl) ethyl pivalate 3 have been examined as monomeric models for poly-2-(9-anthryl)ethyl methacrylate 1. The absorption and excitation spectra of 2 show no ground state interaction, but appreciable monomer (51%) and excimer (49%) emission. Delayed monomer and excimer fluorescence are also observed in fluid solution at room temperature. Photolysis of 2 at low temperature produces a photoproduct (44% yield) which is unstable at room temperature and presumably is the head-to-head (H-H) dimer. Steady state irradiation of 2 at room temperature (Λ 350 nm) cleanly produces a head-to-tail (H-T) dimer (6) derived from the singlet state and an additional unidentified adduct (7). The product distribution is concentration dependent, with 6 predominating at high concentrations (> 10⁻³ M ). The fluorescence spectra of the broken dimers derived from 6 and 7 indicate that substantial ir overlap exists in the transition state leading to each product.     

A fluorescent molecular switch driven by the input sequence of metal cations: an azamacrocyclic ligand containing bipolar anthracene fragments

An azamacrocyclic ligand (L) containing two anthracene (AN) fragments connected through two triethylenetetramine bridges has been synthesized, in which each of the bridges can coordinate with one metal cation. The effects of pH and metal cations (Zn2+ and Cd2+) on the emission properties of L were studied in water. Without metal cations, L does not show any emission at basic pH values. The addition of Zn2+ leads to the production of excimer emission, which is due to a static excimer formed by direct excitation of the intramolecular ground-state dimer of the bipolar AN fragments that approach each other by Zn2+ binding. In contrast, Cd2+ addition does not result in excimer emission because the Cd2+-AN pi complex, formed by donation of a pi electron of the AN fragments to the adjacent Cd2+, suppresses pi-stacking interactions of the AN fragments. The most notable feature is the appearance of excimer emission controlled by the input sequence of metal cations: Zn2+-->Cd2+ sequential addition (each one equivalent) allows excimer emission, whereas the reverse sequence (Cd2+-->Zn2+) does not. In the Zn2+-->Cd2+ sequence, Cd2+ coordination is structurally restricted by the first Zn2+ coordination with the other polyamine bridge, leading to the formation of a weak Cd2+-AN pi complex. In contrast, for the reverse sequence, the first Cd2+ coordination forms a stable Cd2+-AN pi complex, which is not weakened by sequential Zn2+ coordination, resulting in no excimer emission.     

Photophysical study of bis(naphthalimide)-amine conjugates: toward molecular design of excimer emission switching

The fluorescence properties of two bis(1,8-naphthalimides) with amino-containing spacers are investigated, giving special emphasis to the observation of excimer emission. It is found that a minor elongation of the spacer by two methylene units gives rise to a quantitative shut-down of the broad and red-shifted excimer emission. Furthermore, a switching of this emission is established through manipulation of a photoinduced electron transfer process, which involves the amino spacer. Protons as well as protic solvents lead to substantial excimer emission with lifetimes of 12 to 27 ns. The excimer quantum yield takes a maximum value of Φ(f) = 0.07 (acetonitrile with 1 equiv trifluoroacetic acid). The increased virtual Stokes shifts (ca. 150 nm) as compared to the fluorescence of monomeric 1,8-naphthalimides are an alternative approach to obtain colored, significant, and long-lived fluorescence from these chromophores. As an additional excited state pathway, the occurrence of homo-Fo?rster resonance energy transfer (homo-FRET) is established by fluorescence polarization measurements and calculation of the corresponding critical Fo?rster radius (R(0) ca. 13 ?). The average interchromophore distance between the naphthalimides is estimated as 7.5 ? and 9.5 ? for the dyad with the shorter and the longer spacer, respectively. These observations and the absence of a rise time component for excimer emission are in agreement with the formation of a "loose" ground state dimer, which upon excitation undergoes a fast geometrical adjustment to the excimer structure where the chromophores are at contact distance.     

Molecule-binding dependent assembly of split aptamer and γ-cyclodextrin: A sensitive excimer signaling approach for aptamer biosensors

A highly sensitive and selective fluorescence aptamer biosensors for the determination of adenosine triphosphate (ATP) was developed. Binding of a target with splitting aptamers labeled with pyrene molecules form stable pyrene dimer in the γ-cyclodextrin (γ-CD) cavity, yielding a strong excimer emission. We have found that inclusion of pyrene dimer in γ-cyclodextrin cavity not only exhibits additive increases in quantum yield and emission lifetime of the excimer, but also facilitates target-induced fusion of the splitting aptamers to form the aptamer/target complex. As proof-of-principle, the approach was applied to fluorescence detection of adenosine triphosphate. With an anti-ATP aptamer, the approach exhibits excimer fluorescence response toward ATP with a maximum signal-to-background ratio of 32.1 and remarkably low detection limit of 80 nM ATP in buffer solution. Moreover, due to the additive fluorescence lifetime of excimer induced by γ-cyclodextrin, time-resolved measurements could be conveniently used to detect as low as 0.5 μM ATP in blood serum quantitatively.     

Spectroscopic studies of the conformational properties of naphthoyl chitosan in dilute solutions

A naphthoyl chitosan derivative was prepared, and its conformations in dilute solutions were characterized with spectroscopic methods, including circular dichroism (CD) spectroscopy and fluorescence emission spectroscopy. The CD spectrum of this polymer showed a negative band at about 295 nm in dimethyl sulfoxide (DMSO), indicating that the polymer adopted a helical secondary structure. A helix reversion occurred at concentrations greater than 1 mg/mL. The intensity of the CD signal decreased with the addition of water to the solution, and this suggested a change from a helical conformation to a looser one as a result of the collapse of intramolecular hydrogen bonds. In the fluorescence emission experiments, two kinds of excimer emission bands were detected at 375 and 425 nm, and they were assigned to a partially overlapped dimer with a twisted geometry and a fully overlapped dimer with a sandwichlike geometry, respectively. Adding water to a solution of naphthoyl chitosan in DMSO resulted in a gradual reduction of the emission intensity at 375 nm, and this implied that the twisted arrangement of the chromophore was destroyed by the presence of water. The relative intensity (i.e., the ratio of the intensity of the excimer emission at 425 nm to that of the excimer emission at 375 nm) depended on the solvent (DMSO, N,N‐dimethylformamide, N,N‐dimethylacetamide, and 1‐methyl‐2‐pyrrolidinone), and this indicated that the conformation of naphthoyl chitosan was solvent‐dependent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2747–2758, 2004     

疏水作用对光化学和光物理过程的影响 V: 1,3-二萘基丙烷在不良溶剂中的分子构象和激基缔合物的形成

本文研究了1,3-二(α-萘基)丙烷(ααDNP)和1,3-二(β-萘基)丙烷(ββDNP)在乙二醇-水(EG-H2O)混合溶剂中的吸收光谱、荧光光谱以及时间分辨荧光光谱, 发现在-196至60℃范围内, 疏水效应使ααDNP和ββDNP分子采取两个萘环彼此靠近相互平行的构象, 并且两个萘环间有很强的相互作用, 形成基态配合物(二聚体), 受激后只显示二聚体荧光. 高于60℃, 二聚体分解, 受激后显示单体和激基缔合物荧光.     

Effects of metal cation coordination on fluorescence properties of a diethylenetriamine bearing two end pyrene fragments

Fluorescence properties of a diethylenetriamine bearing two end pyrene fragments (L) have been studied in water, where effects of adding metal cations (Zn2+, Cd2+, Cu2+, Hg2+, Ag+) on the emission properties of L have been studied. Without metal cations, L shows dual-mode fluorescence consisting of monomer and excimer emissions. The monomer emission intensity (I(M)) is strong at acidic pH but decreases with a pH increase because of an electron transfer (ET) from the unprotonated nitrogen atoms to the excited pyrene fragment. The excimer emission is due to the static excimer formed via a direct photoexcitation of the intramolecular ground-state dimer (GSD) of the end pyrene fragments. The excimer emission intensity (I(E)) is weak at acidic pH but increases with a pH increase because of the GSD stability increase associated with the deprotonation of the polyamine chain. Addition of metal cations leads to I(M) decrease, where chelation-driven I(M) enhancement does not occur even with diamagnetic Zn2+ and Cd2+ at any pH. This is because a pyrene-metal cation pi-complex, formed via a donation of pi-electron of the pyrene fragment to the adjacent metal center, suppresses the monomer photoexcitation. I(E) also decreases upon addition of metal cations because the pyrene-metal cation pi-complex weakens pi-stacking interaction of the end pyrene fragments, leading to GSD stability decrease. The emission properties of L-Zn2+ complexes were studied by means of time-resolved fluorescence decay measurements, and the effects of adding a less-polar organic solvent were also studied to clarify the detailed emission properties.     

Theoretical investigations of the perylene electronic structure: Monomer,dimers, and excimers

The structural and electronic properties of perylene molecule, dimers, and excimers have been computationally studied. The present work represents the first systematic study of perylene molecule and dimer forms by means of long‐range corrected time‐dependent density functional theory (TDDFT) approaches. Initially, the study explores the photophysical properties of the molecular species. Vertical transitions to many excited singlet states have been computed and rationalized with different exchange‐correlation functionals. Differences between excitation energies are discussed and compared to the absorption spectrum of perylene in gas phase and diluted solution. De‐excitation energy from the relaxed geometry of the lowest excited singlet is in good agreement with the experimental fluorescence emission. Optimization of several coplanar forms of the perylene pair prove that, contrary to generalized gradient approximation (GGA) and hybrid exchange‐correlation functionals, corrected TDDFT is able to bind the perylene dimer in the ground state. Excitation energies from different dimer conformers point to dimer formation prior to photoexcitation. The fully relaxed excimer geometry belongs to the perfectly eclipsed conformation with D_2h symmetry. The excimer equilibrium intermolecular distance is shorter than the separation found for the ground state, which is an indication of stronger interchromophore interaction in the excimer state. Excimer de‐excitation energy is in rather good agreement with the excimer band of perylene in concentrated solution. The study also scans the energy profiles of the ground and lowest excited states along several geometrical distortions. The nature of the interactions responsible for the excimer stabilization is explored in terms of excitonic and charge resonance contributions. © 2015 Wiley Periodicals, Inc.     

Supramolecular assembly system depended on guest species based on bis-naphthane modified β-cyclodextrin dimer

The supramolecular assembly system based on bis naphtahlene modified β-cyclodextrin dimer linked with ethylenediamine unit was studied. The synthesis of the titled compound (β-1) was succeeded in a 7% synthetic yield. It was observed that β-1 showed monomer emission, which was decreased concurrently with appearance of excimer emission in an addition of guest species such as 1-adamantanol or ursodeoxycholic acid. When γ-CyD was added to the system, two types of fluorescent spectra were obtained, which was depended on guest species. It was indicated that both of naphthalene units of β-1 were included in the γ-CyD cavity in the presence of 1-adamantanol in a fashion of 2:1 complex. On the other hand, an addition of ursodeoxycholic acid gave disappearance of the excimer emission as well as increase of monomer emission. In the system, each of the appended units was trapped by the each of two γ-CyDs, which is 2:2 complex formation.     

Electronic states of the benzene dimer: a simple case of complexity

Electronic structure calculations of the excited states of the benzene dimer using equation-of-motion coupled-cluster method are reported. The calculations reveal large density of electronic states, including multiple valence, Rydberg, and mixed Rydberg-valence states. The calculations of the oscillator strengths for the transitions between the excimer state (i.e., the lowest excited state of the dimer, 1(1)B(1g)) and other excited states allowed us to identify the target state responsible for the excimer absorption as the E(1u) state of a mixed Rydberg-valence character at 3.04 eV above the excimer (1(1)B(1g)). Although at D(6h) the 1(1)B(1g) → E(1u) transition is symmetry-forbidden, small geometric displacements (to D(2h)) that have a negligible effect on the excitation energy split this degenerate state into the dark (4B(3u)) and bright (4B(2u)) components (oscillator strength of 0.3 au). The excitation energy for this transition depends strongly on the dimer structure, which explains the broad character of the experimentally observed excimer absorption spectrum.     

Self-organization of 1-methylnaphthalene on the surface of artificial snow grains: a combined experimental-computational approach

A combined experimental-computational approach was used to study the self-organization and microenvironment of 1-methylnaphthalene (1MN) deposited on the surface of artificial snow grains from vapors at 238 K. The specific surface area of this snow (1.1 × 10(4) cm(2) g(-1)), produced by spraying very fine droplets of pure water from a nebulizer into liquid nitrogen, was determined using valerophenone photochemistry to estimate the surface coverage by 1MN. Fluorescence spectroscopy at 77 K, in combination with molecular dynamics simulations, and density functional theory (DFT) and second-order coupled cluster (CC2) calculations, provided evidence for the occurrence of ground- and excited-state complexes (excimers) and other associates of 1MN on the snow grains' surface. Only weak excimer fluorescence was observed for a loading of 5 × 10(-6) mol kg(-1), which is ～2-3 orders of magnitude below monolayer coverage. However, the results indicate that the formation of excimers is favored at higher surface loadings (>5 × 10(-5) mol kg(-1)), albeit still being below monolayer coverage. The calculations of excited states of monomer and associated moieties suggested that a parallel-displaced arrangement is responsible for the excimer emission observed experimentally, although some other associations, such as T-shape dimer structures, which do not provide excimer emission, can still be relatively abundant at this surface concentration. The hydrophobic 1MN molecules, deposited on the ice surface, which is covered by a relatively flexible quasi-liquid layer at 238 K, are then assumed to be capable of dynamic motion resulting in the formation of energetically preferred associations to some extent. The environmental implications of organic compounds' deposition on snow grains and ice are discussed.