Excimer

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

Electronic Spectra of Jet-Cooled Anthracene Dimer: Evidence of Two Isomers in the Electronic Ground State

Abstract: The broad and sharp absorption systems of anthracene in the 362−376 nm region have been confirmed to be due to dimeric species by measuring the resonantly enhanced two-photon ionization mass spectrum. The hole-burning spectrum indicated that two stable isomers exist in the S0 state. The decay time of the excimer emission (300 ns) from the broad system is much longer than that of the emission from the sharp system (15 ± 5 ns), indicating that the electronic nature of the excited state is very different between the two systems. The difference in the excited-state potentials of the two systems has been discussed on the basis of the vibronic structures and the emission lifetimes.

Semiempirical Molecular-Orbital Calculations. VI. Dimers of Benzene

Abstract: Semiempirical charge self‐consistent MO calculations have been carried out for a large number of benzene dimers of different geometric conformations (e.g., D6h, C2h, S2, C6, S12, C2υ, etc.). It has been found that the most stable excimer conformation is not the most symmetric (i.e., D6h), but rather one in which the rings are rotated relatively about the D6h axis and/or tilted, one with respect to the other. The lifetime of excimer fluorescence can be satisfactorily explained in two ways: (1) The transition is made vibronically allowed in much the same way as the 1B2u→1A1gtransition of benzene; or (2) the excimer possesses C1 or C2υ symmetry, in which case a very small relative tilting of the benzene planes can induce transition moments of proper magnitude without invoking vibronic effects at all. A number of suggestions are made concerning solvent effects, and the presence of underlying continua in discrete absorption spectra, etc. In particular, a concept of contact excimer absorption is broached and ra...

'Excimer’ fluorescence III. Lifetime studies of 1:2-benzanthracene derivatives in solution

Abstract: Observations were made of the fluorescence lifetimes of 1:2-benzanthracene and fourteen of its methyl derivatives in dilute deoxygenated cyclohexane solutions. 1:2-benzanthracene and its 5-, 6- and 10-methyl derivatives were also studied in more concentrated solutions. The time response functions of the monomer and excimer fluorescence components were measured by two independent methods, namely the phase and modulation fluorometer and the pulsed light source techniques. The quantum efficiency of the monomer fluorescence in dilute solutions, and the relative excimer/monomer fluorescence yield I D I M in concentrated solutions, were also observed. The results are analyzed to determine the rate parameters of monomer and excimer fluorescence and of excimer formation and dissociation. It is found that only about half the collisions between excited and unexcited monomers result in excimer formation. This behaviour differs from that of pyrene and it is indicative of weaker excimer interaction in the 1:2-benzanthracene derivatives. The factors determining I D I M are discussed.

Solvent effects on intramolecular excimer formation in n-acetyl-bis(pyrenylalanine)-methylester

Abstract: — The synthesis, absorption and emission properties of threo and erythro N-acetyl-bis-(pyrenylalanine)-methylester are discussed. The intensity of excimer emission is very dependent on the tendency of the solvent to interact with the peptide function by hydrogen bonding. Hydrogen accepting solvents shift the equilibrium between the different conformations, adopted by these dipeptides, towards a random coil conformation, which is unfavourable for excimer formation. In strongly hydrogen donating solvents however, a very intense excimer emission is observed due to a reduction of the partial double bond character of the peptide bond by an hydrogen bridge with the solvent molecules.

Zinc-specific intramolecular excimer formation in TQEN derivatives: fluorescence and zinc binding properties of TPEN-based hexadentate ligands

Abstract: Zn2+-induced fluorescence enhancement of the TPEN (N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine)-based ligand, N,N-bis(1-isoquinolylmethyl)-N′,N′-bis(pyridylmethyl)ethylenediamine (N,N-1-isoBQBPEN, 1b), has been investigated. Upon Zn2+ binding, 1b shows a fluorescence increase (ϕZn = 0.028) at 353 and 475 nm. The fluorescence enhancement at longer wavelengths is due to intramolecular excimer formation of two isoquinolines and is specific for Zn2+; Cd2+ induces very small fluorescence at 475 nm (ICd/IZn = 10%). The excimer formation of the [Zn(1b)]2+ complex in the excited state is supported by the time-dependent DFT calculation. Neither long-wavelength fluorescence nor excimer formation is observed in the Zn2+ complex of N,N′-1-isoBQBPEN (2b). The quinoline analog N,N-BQBPEN (1a) exhibits similar but significantly smaller excimer formation. Thermodynamic and kinetic comparisons of Zn2+ binding properties of ethylenediamine-based hexadentate ligands with pyridines and (iso)quinolines are comprehensively discussed.