Excimer emission in 9-aminoacridine hydrochloride

Excimer emission in concentrated aqueous solutions of 9-aminoacridine hydrochloride has been observed at 555 nm. A study of monomer, dimer and excimer emission, absorption and excitation spectra shows that the excited dimer emission is transformed into excimer emission at higher temperatures. Unusually large hypochromism is observed on dimer formation.     

Fluorescence sensing of tartaric acid: a case of excimer emission caused by hydrogen bond-mediated complexation

A novel quinoline based receptor that shows monomer emission quenching followed by intramolecular excimer emission upon hydrogen bond mediated complexation of tartaric acid has been designed and synthesized. The excimer emission has been used to confirm the selective recognition of tartaric acid over its nonhydroxy analogue, succinic acid. Binding ability was studied by ¹H NMR, UV-vis and fluorescence spectroscopic methods.     

Resolution of ultrafast pyrene excimer emission rise times in zeolites X and Y

Pyrene has been a favorite photophysical probe molecule for zeolite research because of its ability to exhibit both monomer and excimer emission upon excitation. This study combines the use of ultrafast time-resolved fluorescence spectroscopy with steady-state fluorescence spectroscopy to study the excimer emission of pyrene incorporated within zeolites LiY, NaY, KY and NaX. The effects of sealing technique and coincorporated solvents are also explored. Pyrene excimer emission is resolvable with the use of an ultrafast streak camera under all conditions examined in this study with a rise-time range of 6.8 to 16.0 picoseconds. For each zeolite sample the addition of cosolvents decreases the rise time, with a greater decrease for polar solvents than for a nonpolar solvent. The presence of a detectable rise time for excimer emission indicates that pyrene excimer formation is a dynamic process when pyrene is embedded within the cavities of zeolite host materials.     

Excimer Emission of Pyrene-l-Butyric Acid in Aqueous Solution of Sodium Dodecyl Sulfonate below Critical Micelle Concentration

Excimer emission of ionic pyrene derivatives in ionic surfactant solutions has been observed. However, the reports were concerning on the excimer emission of charged pyrene derivatives in the presence of oppositely charged surfactant, in those cases the excimer formation was reasoned as surfactant induced aggregation of fluorophore through both hydrophobic and electrostatic interactions.     

Interaction of pyrene-end-capped poly(ethylene oxide) with bovine serum albumin and human serum albumin in aqueous buffer medium: a fluorometric study

The photophysical behavior of a hydrophobically tailored water-soluble polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), has been studied in aqueous buffered bovine serum albumin (BSA) and human serum albumin (HSA) media. In buffered aqueous solution the polymer shows dual emission corresponding to the monomer and the excimer of pyrene moiety. The relative intensity of the monomer to the excimer emission shows interesting variation with the addition of BSA and HSA and is indicative of significant interaction of these albumin proteins with the polymer. The binding interaction has been shown to have a prominent role on the steady state fluorescence anisotropy of the two emission bands. Attempt has been made to determine the micropolarities of the protein microenvironments from a comparison of the variation of the monomer to excimer relative fluorescence intensities of the probe in water–dioxane mixtures with varying composition.     

Immobilization of pyrene on quartz plate surface via a flexible long spacer and its sensing properties to dicarboxylic acids

It is known that polycyclic aromatic hydrocar-bons (PAHs) form excimer easily, and show both monomer and excimer emission in polar medium[1]. This character comes from their hydrophobic nature and plane structures. The ratio of the intensity of ex-cimer emission to that of monomer emission is a func-tion of distance between neighbouring PAHs in a sys-tem. It is not difficult to understand that many factors, such as the concentration of PAHs, temperature, pres-ence and concentration of othe…     

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.     

Processes of molecular association and excimeric emission in protonated N,N-dimethylformamide

Formation of associates of N,N-dimethylformamide (DMF) molecules was studied to clarify their role in photoluminescent activity of protonated DMF solutions. The association of DMF molecules was observed in dilute aqueous solutions at concentrations of DMF above approximately 4x10(-2) M. The association is enhanced when the CO bond of the DMF molecule is activated by protonation with hydrochloric acid, which leads to appearance of an excimeric emission at approximately 530 nm. The excitation spectrum of the excimeric emission showed the excitation maximum in the region of the absorption of DMF associates, which is a first evidence of a more complex mechanism of excimer formation originating from excitation of associated rather than monomeric molecules in the ground state. A simple approach was provided to evaluate a number of molecules in the excimer structure. An original theory has been developed, and it was calculated that the DMF excimer has a dimeric nature. A model of the excimer formation was proposed, which suggests that a hydrogen-bonded associate is an intermediate form leading to the excimeric structure upon excitation. It was observed that DMF possesses also a monomeric emission with the emission maximum at approximately 385 nm, which was attributed to the intramolecular charge-transfer process. It has been found that the change in structure of the DMF associates via the liquid-solid phase transition affects both excitation and emission bands of excimers, so that the excimeric emission shifts to the blue region and intermixes with the emission of DMF monomers.     

Multiple Photoluminescent Processes from Pyrene Derivatives with Aggregation‐ and Mechano‐Induced Excimer Emission

Two novel pyrene‐based isocyanide gold(I) complexes have been designed and synthesized. The different structures lead to distinct and diverse photophysical properties both in solution and in the aggregate state. Multiple photoluminescence, involving monomer emission, locally excited emission and excimer emission, are observed. Notably, an excimer is formed by aggregation in solution and external mechanical stimulation in the solid state, showing aggregation‐ and mechano‐induced excimer emission.     

Double Naphthalene‐Tagged Cyclodextrin‐Peptide Capable of Exhibiting Guest‐Induced Naphthalene Excimer Fluorescence

A cyclodextrin‐peptide hybrid (17NNβ) bearing two naphthalene units in the peptide side chain has been designed and synthesized as a novel chemosensor molecule. Circular dichroism study of the compound revealed that the peptide has α‐helix structure with a helix content of 41%. The peptide revealed both monomer and excimer emission and the intensity of the excimer emission increased while that of the monomer emission decreased upon addition of the guest compound. This behavior was observed for various guest molecules, suggesting that the system can be used for detecting molecules in aqueous solution.     

Excimer luminescence of 9-cyanoanthracene under pressure

The excimer emission of 9-cyanoanthracene has been measured at room temperature as a function of pressure. Near 8 kbar the luminescence undergoes a drastic shift to lower energies corresponding to a change of the emitting excimer from the trans, head-to-tail, to the cis, head-to-head, molecular pair. The latter excimer deactivates the photodimerization reaction due to the absence of the topochemically preformed geometry in the excited state which would favour the trans-photoproduct.     

On the relationship between fluorescnece and molecular geometry. The effect of intermolecular shift on the excimer emission of crystalline dianthronylidene ethane.

The existence of two luminescent excimer geometries in polymorphic dianthronylidene ethane has been verified by X-ray structure determinations of three crystal modifications. The different excimer emission energies are interpreted in terms of variations in transannular π-orbital interaction resulting from an intermolecular shift of adjacent molecules across the log axis of the anthronylidene moiety.     

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.     

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.     

新型三嗪桥连的双1,8-萘酰亚胺衍生物的合成及其光物理行为

以1,8-萘酰亚胺和三聚氯氰为主要原料, 合成了两种由三嗪环桥连的双1,8-萘酰亚胺化合物3 和5. 采用紫外-可见光谱和荧光光谱等手段考察了两种化合物在不同溶剂中的光物理行为. 与参比化合物N-丁基-1,8-萘酰亚胺相比, 在二氯甲烷、三氯甲烷和甲醇等极性溶剂中, 化合物3和5除了在短波区(λ<400 nm)存在1,8-萘酰亚胺的特征荧光发射峰外, 在长波区(>450 nm)均产生一个较强的新荧光发射峰, 表现出分子内激基缔合物的光物理行为. 与化合物5相比, 由于化合物3特殊的构象异构, 其荧光强度发生严重的猝灭. 在非极性溶剂甲基环己烷中, 化合物5 由于存在较强的分子间氢键作用而聚集, 受激后形成了较稳定的分子间激基缔合物, 但未观察到明显的分子内激基缔合物的形成. 在甲苯溶剂中, 化合物3和5与甲苯分子形成了激基复合物, 并未形成分子内激基缔合物. 进一步研究3和5的固态激发态性质, 发现化合物3和5的固体薄膜受激后分别在465和469 nm处出现激基缔合物的特征荧光发射峰.     

Cu2+-induced blue shift of the pyrene excimer emission: a new signal transduction mode of pyrene probes

A pentiptycene-bispyrenyl system (1) has been synthesized and investigated as a fluorescent chemosensor for metal ions. A novel blue shift along with an intensity enhancement of the pyrene excimer emission is observed for 1 in the presence of Cu(2+). Such a new signal transduction mode of pyrene probes results from the formation of a static pyrene excimer that has very different characteristics from its dynamic counterpart.     

A 3-dimensional spiro-functionalized platinum(II) complex to suppress intermolecular π-π and Pt···Pt supramolecular interactions for a high-performance electrophosphorescent device

A 3-D platinum(II)-based spirometal complex has been designed and synthesized to suppress aggregation and excimer emission. A prototype phosphorescent organic light-emitting device exhibits the high-performance orange emission with an external quantum efficiency of up to 5.2%.     

溶液中聚电解质分子内激态缔合体的形成

采用荧光分光光度法,实验测定了聚苯乙烯磺酸钠在无盐和有盐的水溶液中,单体和激态缔合体的荧光发射光谱.结果表明:激态缔合体单体发射强度比I_E/I_M随外加盐种类、浓度和价态而变化.在相同盐浓度下,各体系的I_E/I_M次序为:KCl>NaCl>LiCl和CaCl_2>MgCl_2。 也研究了NaCl水溶液中聚电解质分子的荧光猝灭.结果表明:随外加盐浓度逐渐增大,聚电解质分子由类棒状向无规线团状转化,该状态有利于激态缔合体的形成.     

THE 1-CYANONAPHTHALENE EXCIMER IN HOMOGENEOUS AND MICELLAR SOLUTIONS

Abstract— An excimer of 1-cyanonaphthalene is produced in homogeneous organic solvents and in micelle containing detergent solutions. From solvent effects in homogeneous solution it is concluded that the excimer is relatively polar (dipole moment ∼ 4D). From a comparison with emission from that observed in homogeneous solvents, it is concluded that 1-cyanonaphthalene is solubilized mainly in the Stern Layer of sodium dodecyl sulfate (SDS) and hexadecyltrimethyl ammonium bromide (HDTBr) micelles. The influence of variation of detergent concentration on the excimer to monomer emission ratio and the influence of NaCl concentration on the excimer to monomer emission ratio have been determined. Excimer formation is shown to be a convenient method for determination of the Kraft point of SDS solutions.     

Luminescent Radical‐Excimer: Excited‐State Dynamics of Luminescent Radicals in Doped Host Crystals

The excited‐state dynamics of the photostable luminescent organic radical (3,5‐dichloro‐4‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl (PyBTM) doped in a host crystal was investigated by using optically detected magnetic resonance (ODMR) and time‐resolved emission spectroscopies. In the radical system, the unpaired electron can be used as the probe for studying the electronic state and its dynamics. The mixed crystal with a high concentration of the radical showed excimer emission, together with the monomer emission. The ODMR signals were observed with opposite signs for monitoring the monomer and the excimer emissions. Based on their temperature and concentration dependencies, the excited‐state dynamics on the doped crystal and the mechanism of the excimer formation and the ODMR signal generation are discussed with the help of the quantum mechanical simulation of the excited‐state spin dynamics. The initial process of excimer formation has been clarified for the first time from the viewpoint of the spin‐dynamics.