Excimer

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

Discrete face-to-face stacking of anthracene inducing high-efficiency excimer fluorescence in solids via a thermally activated phase transition

Abstract: It is always a challenge for planar polycyclic aromatic molecules to achieve high efficiency in solids owing to their frequent encounter with aggregation-caused quenching (ACQ). An anthracene derivative with one-side meta-substituted triphenylamine (TPA) was found to show high-efficiency excimer fluorescence (ηPL = 76.8%) in G-phase (green) crystals as well as a long lifetime, in sharp contrast with that of a monomer in a doped film (ηPL = 36.6%) and that of B-phase (blue) crystals (ηPL = 8.1%). In essence, the excimer-induced enhanced emission can be ascribed to the special intermolecular stacking in the solid state, namely, discrete antiparallel dimeric stacks between anthracene moieties in G-phase crystals, which are responsible for greatly suppressed non-radiative deactivation due to a uniform emissive state preventing the formation of an energy-trapping “dark” state. Moreover, a G-phase could be obtained through a thermally-activated phase transition from B-phase crystals, corresponding to the completely synchronized change of fluorescence properties. The present results consolidate a novel strategy of designing discrete dimeric stacking of planar polycyclic aromatic molecules to achieve high-efficiency fluorescence in the solid state by an excimer-induced enhanced emission (EIEE) mechanism.

Electrogenerated Chemiluminescence. 76. Excited Singlet State Emission vs Excimer Emission in Ter(9,9-diarylfluorene)s

Abstract: The electrochemistry and electrogenerated chemiluminescence (ECL) of two ter(9,9-diarylfluorene)s, TDAFs, were investigated. The ECL from these new blue emitters produced by ion annihilation showed spectra with significant emission at longer wavelengths and was different from their fluorescence spectra. This was ascribed to the formation of excimers. Excimer emission was not observed in ECL during the reduction of the TDAFs with benzoyl peroxide (BPO) as a coreactant, where the ECL spectra were essentially the same as their fluorescence spectra, consistent with the requirement of ion annihilation for excimer production. Excimer emission is not seen in fluorescence, even at relatively high concentrations, because of the short lifetime of 1 TDAF*. The quantum yields, ECL, for the ECL by ion annihilation were 0.05% for TDAF-1 and 0.01% for TDAF-2. ECL with BPO as a coreactant produced 8% (TDAF-1) or 3% (TDAF-2) of the ECL intensity of Ru(bpy)3 2+ generated under the same conditions (0.5 mM TDAF or Ru(bpy)3 2+ /5 mM BPO).

Excimer ablation of human intervertebral disc at 308 nanometers.

Abstract: Excimer laser energy, which has been shown to photoablate tissue at a precisely controllable rate with minimal thermal damage, was applied to human intervertebral disc in an effort to develop a technique for percutaneous discectomy. Cadaveric samples of human disc were used. Excimer laser energy was produced by a XeCl, magnetically switched, long-pulse laser working at 308 nm, 20 Hz. Annulus tissue of approximately 1 mm thickness was placed in contact with the output tip of a 400 microns core diameter quartz fiber, and measurements of ablation rate were made at different radiant exposures. Ablation rates were found to vary linearly with radiant exposure, from 0.7 micron/pulse at 10 mJ/mm2 to 11.0 microns/pulse at 55 mJ/mm2, with a correlation coefficient of 0.984. Threshold radiant exposure, calculated by extrapolation, was found to be about 7 mJ/mm2. Histologic analysis showed a minimum of thermal damage in these specimens, and when ablated with modification to maintain constant fiber-tissue contact, thermal injury was nearly absent, as compared to samples ablated with Nd:YAG through a contact probe. Thermographic analysis, performed using the AGA 782 Digital Thermography system, showed increasing temperature with increasing radiant exposure, with a maximum temperature of 47.2 degrees C at 55 mJ/mm2. In that precise tissue ablation was demonstrated with minimal generated heat, and excimer energy at 308 nm is transmissible through fiber optics, excimer holds great promise for the development of a percutaneous discectomy technique.

Energy of Excimer Luminescence. III. Group Theoretical Considerations of Molecular Exciton and Charge Resonance States

Abstract: The excimer formed by two identical molecules of D2h or D6h point groups is discussed group theoretically. The manner in which excimer geometry influences configuration interactions between molecular exciton states and charge‐resonance states, and the conditions necessary to resonance stabilization of the ground state are delineated. The polarizations of the transitions between the ground state and the various excited excimer states and of that between two excimer excited states are discussed. Some computational results for the D6h benzene excimer are presented.