Naphthalene Excimer Fluorescence Research Articles

Computational Evidence of Inversion of (1)La and (1)Lb-Derived Excited States in Naphthalene Excimer Formation from ab Initio Multireference Theory with Large Active Space: DMRG-CASPT2 Study.

The naphthalene molecule has two important lowest-lying singlet excited states, denoted (1)La and (1)Lb. Association of the excited and ground state monomers yields a metastable excited dimer (excimer), which emits characteristic fluorescence. Here, we report a first computational result based on ab initio theory to corroborate that the naphthalene excimer fluorescence is (1)La parentage, resulting from inversion of (1)La and (1)Lb-derived dimer states. This inversion was hypothesized by earlier experimental studies; however, it has not been confirmed rigorously. In this study, the advanced multireference (MR) theory based on the density matrix renormalization group that enables using unprecedented large-size active space for describing significant electron correlation effects is used to provide accurate potential energy curves (PECs) of the excited states. The results evidenced the inversion of the PECs and accurately predicted transition energies for excimer fluorescence and monomer absorption. Traditional MR calculations with smaller active spaces and single-reference theory calculations exhibit serious inconsistencies with experimental observations.

Supramolecular complexes of spin-labeled and luminescent molecules with cyclodextrins

Studies on the structure, molecular dynamics, and spectral-luminescent properties of the guesthost cyclodextrin (CD) complexes which were carried out in the Photochemistry Center and the Institute of Chemical Problems, Russian Academy of Sciences (RAS), in the period of 2000–2011 are reviewed. In a series of studies, the binary and ternary CD complexes in aqueous solutions, in the solid phase, and on silicawater and silica-gas interfaces were investigated. The spin-labeled analogs of the biologically active molecules (indoles, fatty acids, and cholesterol) were used as models of the functional guest molecules in these complexes. The use of various EPR approaches made it possible to determine the character of rotational motion and its quantitative parameters (rotational frequencies and angular amplitudes) for guest molecules in the CD cavities and to reveal the effects of the second and third guest molecules and of the covalent binding of CDs to silica microspheres on molecular dynamics, as well as the hydrophobicity of the environment for the spin-labeled molecules. The properties of the β-CD and γ-CD complexes of naphthalene and its derivatives were studied by fluorescence and phosphorescence methods; the effects of the cage compounds (adamantane, carborane, and cyclohexane (CH)), the low-molecular-mass compounds (acetone), and the adsorption on silica of the polymer CD on the appearance and the line shape of the naphthalene excimer fluorescence (EF) and the long-lived phosphorescence were analyzed.

Photodimers of a soluble tetracene derivative. excimer fluorescence from the head-to-head isomer.

[reaction: see text] Irradiation of 5,12-didecyloxytetracene (1) leads to photodimers P(1) (planosymmetric) and P(2) (centrosymmetric). P(1) is characterized by naphthalene excimer fluorescence, whereas P(2) emits naphthalene monomer fluorescence.

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.

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

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

Naphthalene-Tagged Copolymer Micelles Based on Polystyrene-alt-maleic anhydride-graft-poly(ethylene oxide)

Monoamine-terminated poly(ethylene oxide), PEO-NH2 (MW ∼ 5000) has been grafted onto a hydrophobic backbone of polystyrene-alt-maleic anhydride. The backbone has been tagged with a constant fraction of naphthalene and with varying amounts of PEO-NH2. Dialysis from dioxane to 100% water produces micelles that have been characterized by light scattering techniques and TEM. The environment of the polymer backbone as a function of the dioxane/water ratio has been characterized by steady state and time-resolved fluorescence techniques. Backbone collapse seems to occur at ∼50% water based on the growth of naphthalene excimer fluorescence. Micelle aggregation numbers appear to vary inversely with the grafting density according to the relation Nagg ∼ NPEO-3, where NPEO is the number of PEO grafts per chain. This relationship can be rationalized by assuming a constant area per PEO coil on the micelle surface.

Factors affecting the formation in the solid state of the metastable complex between naphthalene and dimethyl-?-cyclodextrin

An equimolar mixture of naphthalene and amorphous heptakis-(2,6-di-O-methyl)-β-cyclodextrin (DMβCD) was heated at 70 or 90°C in a sealed container. After heating ffor 15 min at 90°C, the mixture was crystallized to show an excimer fluorescence of naphthalene, and the fluorescence spectrum changed to a monomer emission by further prolongation of heating time, accompanied by a slight change in its powder X-ray diffractogram. It is suggested that a metastable complex showing the excimer emission of naphthalene was transformed to a stable complex showing the monomer emission. The mixing molar ratio of naphthalene to DMβCD was also found to affect the transformation temperature of the complex.

Photoquenching and the relaxation recovery of naphthalene excimer fluorescence in polymethyl methacrylate matrices

Photoquenching and the relaxation recovery of naphthalene excimer fluorescence in polymethyl methacrylate matrices

Prompt and delayed excimer fluorescence of naphthalene in poly(methyl methacrylate) matrix

The concentration change of prompt and delayed fluorescence spectra of naphthalene in poly(methyl methacrylate) (PMMA) was investigated at 293 and 77 K. For high concentrations, delayed and prompt excimer fluorescence were observed. It is suggested that molecular pairs of naphthalene are responsible for the excimer fluorescence in the PMMA matrix. The ratio φ E/φ M of the excimer fluorescence yield to the molecular fluorescence yield was determined and was found to be considerably larger for the delayed than for the prompt fluorescence. The difference is explained by excitation energy transfer in the triplet state.

Association of Inclusion Compounds of β-Cyclodextrin in Aqueous Solution

Abstract Inclusion compounds in the systems naphthalene–β-cyclodextrin (CDx) and 2-methoxynaphthalene (MN)–o-dicyanobenzene (DB)–β-cyclodextrin in aqueous solution were studied by means of absorption and fluorescence spectra. In the former system a naphthalene excimer fluorescence was observed. By the analyses of the concentration dependence of the absorption spectra and the excimer fluorescence intensities, the species responsible for the excimer fluorescence is identified as a 2:2 inclusion compound which is formed by association of two 1:1 naphthalene–CDx inclusion compounds, not a 2:1 inclusion compound in which two naphthalene molecules enter into the cavity of one CDx molecule. In the latter system, absorption and fluorescence spectra due to a charge transfer complex of MN with DB were observed. By analyses similar to the naphthalene case, the existence of a 1:1:2 association compound formed between a MN–CDx inclusion compound and a DB–CDx inclusion compound is confirmed. Fluorescence quenching by I− and IO3− was also studied for the inclusion compounds in both systems.

The Interaction of Oxygen with Organic Molecules. II. Oxygen Quenching of the Excited States of Adsorbed Aromatic Hydrocarbons

Abstract Quenching of phosphorescence and fluorescence of aromatic hydrocarbons adsorbed on powdered porous glass or silica gel have been examined as a function of oxygen pressure. It has been found that the phosphorescence quenching at low temperature can be explained mostly by assuming that only those aromatic molecules having an oxygen molecule or molecules within an effective interaction radius are nonphosphorescent (static quenching model). The fluorescence quenching occurs only at much higher oxygen pressures and it has been proposed that contact pairs between aromatic and oxygen molecules, which have shorter intermolecular distances compared to the distances effective for the phosphorescence quenching and give rise to the charge-transfer absorption bands, are relevant. It has been observed that the excimer fluorescence of naphthalene appearing at a higher sample concentration is more strongly affected by oxygen than the monomer fluorescence. The emission spectra from naphthalene-porous glass adsorbate immersed in liquid oxygen and nitrogen have also been examined. The formation of the singlet oxygen (1Δg or 1Σg+) through the interaction of oxygen with triplet molecules has been confirmed by use of the peroxidation reaction of adsorbed anthracene.

The Lifetime of Excimer Fluorescence of Naphthalene

Abstract The radiative lifetimes of the excimer fluorescence of naphthalene are calculated for excimers of various geometrical configurations. The results vary, to a great extent, with the configurations, but with a previously-suggested configuration the calculated lifetime is 6×10−6 sec. This is within a factor of 5 of the experimental results.

Energy of Excimer Luminescence. V. Excimer Fluorescence of Naphthalene and Methylnaphthalenes

The interpretation of the energies of excimer luminescence of naphthalene and 12 of its alkyl derivatives is considered, and it is shown (i) that there is considerable configuration interaction between molecular-exciton and charge-resonance states and (ii) that the energy of excimer fluorescence may not be interpreted without invoking this configuration interaction. Excimer-fluorescence energies are calculated for the substituted naphthalenes using a four-electron MO treatment of the interaction and as a function of Z, the Slater orbital effective charge exponent, and of the interplanar distance D. Agreement with excimer-luminescence energies is obtained for values of Z=3.18 and values of D between 3.4 and 3.7 Å, with the largest intermolecular distance D being obtained for those compounds in which steric hindrance is expected to be largest.