Ground and excited state properties of polyamine chains bearing two terminal naphthalene units

摘要

A series of compounds bearing two naphthalene units linked through methylene groups to both ends of differentnopen-chain polyamines has been investigated. The fluorescence emission studies show the presence of an excimernspecies whose formation depends on the protonation state and length of the polyamine chains and implies thenexistence of a bending movement in the excited state allowing the two naphthalene units to approach and interact.nThis interpretation was clearly proven by time-resolved fluorescence with the appearance of double exponentialndecays with a rise time observed at the excimer emission wavelength. For comparison purposes one bis-chromophoricncompound containing a rigid chain, and two mono-chromophoric analogs bearing a single terminal naphthalene unitnwere studied. Their emission spectra show a unique band and the fluorescence decays, are single exponential at pHnvalues where just one species is present in the ground state, showing that in these cases no excimer or exciplex speciesnis formed. The kinetics of excimer formation was used to evaluate the influence of the length and the pH in thenflexibility of the polyamine chain.