Excimer

About: Excimer is a research topic. Over the lifetime, 3725 publications have been published within this topic receiving 75104 citations.

Excimer and Exciplex Formation in van der Waals Dimers of Toluene and Benzene

Abstract: Structural isomerization dynamics of photoexcited van der Waals dimers of toluene and benzene have been investigated by means of fluorescence and mass spectroscopic methods. Two isomeric forms of the heterodimer complex formed between toluene and benzene, assigned to parallel displaced and T-shaped configurations, are found to rearrange into exciplexes when excited in the S1 state with a small amount of vibrational energy. The toluene homodimer also reveals similar excess energy dependence on excimer formation. The excited-state dynamics are contrasted with those of the T-shaped benzene homodimer where no vibrational energy is required for structural isomerization. The excess energy dependence observed for the toluene complexes is attributed to a steric requirement of sandwich-type excimer geometry. Dissociation behavior of these exciplex/excimer complexes has been measured by photodepletion spectroscopy and compared with that of the benzene excimer. These excited-state complexes are found to strongly abs...

Highly ordered pyrene π-stacks on an RNA duplex display static excimer fluorescence

Abstract: The binding and fluorescence properties of complementary RNA sequences attached to different numbers of pyrenes via one carbon linker at the 2′-O-positions have been investigated. Upon hybridization of the pyrene-modified RNA sequences, the modified RNA duplexes with normal thermal stability are formed, and the pyrene arrays are assembled in an inter-strand manner. Because hypochromic effects in the pyrene absorption band and the exciton coupled circular dichroism signals were observed for the pyrene assemblies, the formation of the pyrene array occurs via a π-stacking interaction between the pyrene rings. The pyrene assemblies exhibit strong excimer fluorescence that is characterized by a broad and structureless excitation spectrum. Hence, the excimer is a static excimer due to the direct excitation of the associated pyrenes in the ground state. Based on several spectroscopies, it is revealed that the spatial configuration of the pyrenes in the association is more regulated by the increase in the attached pyrene.

The effect of the nuclear motion on the electronic decay of core hole excited states in molecules

Abstract: We have measured the vibrational fine structure in the electronic decay spectrum of the N 1s→1πg core electron excited state in molecular nitrogen. The Franck–Condon analysis of the vibrational substructure shows that within the 10−14 s lifetime of the core hole excited state the molecule adjusts to the excited state configuration, characterized by a change in bond length by 0.071 A. Interference effects due to the short lifetime of the intermediate state play only a minor role.

Long-Range Diffusion Coefficients in Two-Dimensional Fluid Media Measured by the Pyrene Excimer Reaction†

Abstract: Diffusion-controlled bimolecular reactions in two-dimensional or quasi two-dimensional space are important in both surface and membrane reaction kinetics. A model reaction that has been extensively used to study the dynamics and structure of phospholipid membranes is the formation of the excimer of pyrene. We present experimental evidence that in multilamellar liposomes of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, in the fluid phase at temperatures above phase transition, TL, and for a probe/phospholipid ratio of 1:75, or lower, the fluorescence decay of 1-palmitoyl-2-(1-pyrenodecanoyl)-sn-glycero-3-phosphocholine and the time-resolved emission of the excimer follow a kinetic law specific for two-dimensional diffusion-controlled reactions. The parameters obtained from the application of this law to the experimental results, either from steady-state or from time-dependent fluorescence, give diffusion coefficients, e.g., D(25 °C) = 3.1 × 10-8 cm2 s-1 and an activation energy for diffusion, Ea = 35 k...

Excimer laser material processing : State of the art and new approaches in microsystem technology

Abstract: In this paper the current state of the art and new trends in excimer laser processing of polymer materials are presented. Two processing regimes are of general interest: below and above the ablation threshold. The modification of polymer surface can be carried out by laser processing below ablation threshold. This is successfully demonstrated for the fabrication of optical singlemode waveguides in PMMA for the visible optical range and for 1550 nm. The obtained structures reveal absorption losses in the order of 1.4 dB/cm up to 5 dB/cm. Laser exposure using contact masks or direct scanning of planar structures are appropriate methods for the integration of optical waveguides in PMMA sensor devices (Y-branch). Above the ablation threshold excimer laser micromachining is a powerful tool for a rapid manufacturing of complex three-dimensional micro-structures in polymer surfaces with depths between 0.1 μm and 1000 μm and aspect ratios up to 10. Typical application fields are presented in micro-optics, micro-fluidics and rapid tooling. Micro-Laser-LIGA is established in order to fabricate nebulizer membranes, micro-fluidic devices and integrated single mode waveguides. Furthermore, the fabrication of 3d-shapes in metallic mold inserts is successfully demonstrated. Debris formation is completely suppressed. Polymer structuring with a low power short pulse excimer laser with high repetition rates up to 500 Hz is compared to the structuring with a "conventional" high power excimer laser with a repetition rate of about 10-100Hz as well as with a UV-Nd:YAG (1-2 kHz). These "high-repetition-rateexcimer lasers" with relatively small pulse energies but with much shorter laser pulse duration (< 6 ns) provide a significant improvement of pattern quality. Furthermore, the high repetition rate enables a fast material processing which is discussed in detail for several application fields.