Multiple excimers

For the heavier noble gases, the core multiplicity of the metastable states give rise to eight potential curves (six for 3P2 and two for 2P0). The Ne2 potentials have been calculated by Schneider and Cohen,87 who have also performed scattering calculations for this system. Theoretical and experimental data exist for Ar2,88 whereas only qualitative estimates of the potentials are available for Kr2 and Xe2. These excited states play a prominent role in the rare-gas excimer lasers.89,90 ... 

Exciplexes and excimers have their own structure and properties (e.g. multiplicity, absorption and emission spectra, lifetime, stability constant, enthalpy and entropy content, pathways of deactivation) and can be regarded thus as new chemical species. 

Experimental data on the formation, thermodynamic and kinetic decay parameters, and the multiplicity of exciplexes and excimers involving tetrapyrrole complexes are summarized in Tables 1 and 2. Based on these data and on information on the spectral properties and chemical behavior, some conclusions... 

Excimer-forming complexes (GS = the ground state) Multiplicity of excimer Solvent Formation (K) and decay rate (k, in s ) constants Ref. 

As a fluorescence probe, a TICT compound possesses several merits. It can probe both microviscosity and micropolarity and furthermore, the mode of molecular motion necessary to the TICT phenomenon is well defined and limited to the rotation around a particular bond. This is a difference from intramolecular exciplex or excimer formation in which multiple modes of bond rotation and bending are compounded [7]. Fluorescence polarization studies also can not be free from ambiguity of the mode of rotation [8]. 

Depending upon the spin multiplicity, excimer and exdplexes can be fluorescencent or phosphorescencent. When singlet excited state of the donor molecule interact with the singlet ground state of acceptor molecule, fluorescence excimer/exdplex are formed where as interaction of triplet excited state of donor and triplet state of acceptor gives phosphorescence excimer/exdplex (Fig. 16). 

Monomer and excimer fluorescence decays of Py, 1Py(3)1Py and the alkylpyrenylsilanes PPS and PDS, adsorbed on silica surfaces have been reported in the literature (21, 31-43). However, whereas for inter- and intramolecular excimer formation in homogeneous solution the rate constants of excimer formation and dissociation could be determined from the fluorescence decays (11,15,23), a considerably more complex situation is encountered on the silica surfaces (c.f. Section 3.2.1). This is not surprising, as the multiple adsorption sites at the inhomogeneous surfaces ma)ce different pathways in the excimer formation process li)[Pg.61]

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