Excimer

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

Photophysical Properties of Pyrene-Functionalized Poly(propylene imine) Dendrimers

Abstract: Four generations of poly(propylene imine) dendrimers have been covalently modified with pyrene moieties and examined by fluorescence spectroscopy. Emission and excitation spectra were obtained so that the generational dependence of the dendrimers, especially the extent of steric crowding, could be correlated to the photophysical properties of pyrene. In particular, the effect of dendrimer concentration and generation on pyrene-pyrene interactions was evaluated. More excimer emission was observed for higher generation dendrimers, while little or no evidence for interdendrimer interactions was observed over more than 2 orders of magnitude in dendrimer concentration. Excitation spectra revealed the presence of preassociated pyrene moieties. Protonation of the tertiary amine units was shown to increase monomer fluorescence significantly, while only slightly increasing the observed excimer fluorescence.

Time-dependent density functional study of excimers and exciplexes of organic molecules

Abstract: Organic excimers of pyrene and benzene and an exciplex of styrene with trimethylamine are studied by time-dependent density functional theory (TD-DFT). The performance of the method was first benchmarked on noble gas excimers. Potential curves for low-lying excited states of Ne 2 and Kr 2 are computed using the hybrid functional BH-LYP and the semi-local B-LYP GGA functional. In order to include dispersion (van der Waals) effects, a previously developed R −6 type correction (DFT-D) was applied. The TD-DFT/BH-LYP results are in good agreement with those from CC2 or older MRD-CI treatments while pure GGAs fail miserably. The approach is then used to fully optimise the organic complexes in their ground and excited states. Excited state dissociation energies ( D 0 ) of 0.6, 1.2 and 0.8 eV are obtained for benzene and pyrene excimers and the organic exciplex of styrene and trimethylamine, respectively. For the latter system, the theoretical and experimental values agree to each other within 20%. For the excimers of pyrene and benzene, which have been measured in solution, the deviations are larger but within the range of expected solvent effects. In the case of the pyrene excimer, the TD-DFT/BH-LYP computed order of the low-lying excimer states is in agreement with that predicted by the simple exciton coupling model. The significant decrease of inter-molecular distances for all excited complexes compared to the ground state (0.07–0.4 A) and the reasons for occurring rearrangements (favourable orbital interactions and charge transfer) are discussed.

The excimer lasers.

Abstract: The excimer lasers are a group of lasers that have found wide application in a variety of medical fields including dermatology, cardiology, ophthalmology, and orthopedics. The word excimer refers to excited dimer. These lasers operate in the ultraviolet range, and examples include the 193 nm argon-fluroide, 248 nm krypton-fluoride, 351 nm xenon-fluoride, and of particular interest to dermatology, the 308 nm xenon-chloride. These lasers utilize a mixture of a noble gas and a halogen as a lasing material. They were first used in medicine for their ability to produce cold tissue ablation, but more recently have been used in dermatology as a method of non-ablative phototherapy.

Fluorescent calix[4]arene which responds to solvent polarity and metal ions

Abstract: A calix[4]arene having two pyrene moieties on the lower rim has been synthesized; the ratio of the monomer vs. excimer emission was sensitively affected by solvent polarity and added metal ions.