Excimer

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

Transfer of Electronic Excitation Energy in Polyvinyl Carbazole

Abstract: The energy transfer in amorphous polyvinyl carbazole (PVCA) has been studied by fluorescence quenching experiments using perylene, trinitrofluorenone, and hexachloro‐p‐xylene as guest molecules. The PVCA shows excimer fluorescence. The results are discussed in terms of exciton diffusion and competition between excimer‐forming sites and guest molecules for the trapping of excitons. Single‐step transfer from the excimer state by dipole resonance is considered as an alternative mechanism of energy transfer; in all three cases, however, exciton migration is the more probable energy‐transfer mechanism. The concentration of excimer‐forming sites is estimated to be 10−3 mole/mole basic unit of the polymer. In the pure polymer the exciton covers about a thousand basic units during its lifetime.

Nanosecond and femtosecond excimer laser ablation of fused silica

Abstract: Ablation of fused silica using standard excimer lasers (20–30 ns pulse duration at 193, 248, and 308 nm) and a short pulse laser system (500 fs at 248 nm) is reported. Ablation rates range from several hundred nm/pulse (193 nm or fs-laser) up to about 6 μm/pulse (308 nm). The performance of the ablation is found to depend not only on wavelength and pulse duration but also on the existing or laser induced surface quality (e.g., roughness) of the material. Special ablation phenomena are observed. At 193 nm and moderate fluence (3 J/cm2) ablation takes place at the rear side of a plate without affecting the front side, whereas at higher fluence normal ablation at the front side occurs. At 248 nm (standard excimer) the existence of two consecutive ablation phases is observed: smooth ablation at low rate is followed by explosive ablation at high rate. Using fs-pulses smooth shaped holes are formed during the first pulses, whereas high pulse numbers cause the development of a ripple structure in the ablation craters.

Chloride selective calix[4]arene optical sensor combining urea functionality with pyrene excimer transduction.

Abstract: A neutral 2-site chloride selective compound has been developed (3), based on a 1,3-alternate tetrasubstituted calix[4]arene providing a preorganized supramolecular scaffold. The resultant supramolecular cavity is among the first to combine urea functional groups bridged with single methylene spacers to pyrene moieties. It combines a naturally and synthetically proven H-bonding system with the elegant ratiometric fluorescent signaling properties of an intramolecular pyrene excimer system, triggered by conformational changes upon anion coordination. The excimer emission of 3 is quenched, with a simultaneous rise in the monomer emission solely by the chloride anion among a wide variety of anions tested. 3 has an association constant of 2.4 x 10(4) M(-1) with chloride. The suitability and advantages of ratiometric optical sensor compounds like 3 for use in practical sensor devices is discussed. 3 has an LOD of 8 x 10(-6) M with chloride in acetonitrile-chloroform (95:5 v/v). A dynamic fluorescence study revealed a response time of < 3 s. A recently developed and simple HPLC-based purification method complimented conventional organic work up methods to yield pure product.

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...