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Type: Artigo
Title: Intramolecular, Exciplex-mediated, Proton-coupled, Charge-transfer Processes In N,n-dimethyl-3-(1-pyrenyl)propan-1-ammonium Cations: Influence Of Anion, Solvent Polarity, And Temperature
Author: Safko
Trevor M.; Faleiros
Marcelo M.; Atvars
Teresa D. Z.; Weiss
Richard G.
Abstract: An intramolecular exciplex-mediated, proton-coupled, charge-transfer (PCCT) process has been investigated for a series of N,N-dimethyl-3-(1-pyrenyl)propan-1-ammonium cations with different anions (PyS) in solvents of low to intermediate polarity over a wide temperature range. Solvent mediates both the equilibrium between conformations-of the cation that place the pyrenyl and ammonium groups in proximity (conformation C) or far from each other (conformation 0) and the ability of the ammonium group to transfer a proton adiabatically in the PyS excited singlet state. Thus, exciplex emission, concurrent with, the PCCT process, was observed only in hydrogen-bond accepting solvents of relatively low polarity (tetrahydrofuran, ethyl acetate, and 1,4-dioxane) and not in dichloromethane. From the exciplex emission and other spectroscopic" and thermodynamic data, the acidity of the ammonium group in conformation C of the excited singlet state of PyS (pK(a)(*)) has been estimated to be -34 in tetrahydrofuran. The ratios between the intensities of emission from the exciplex and the locally excited state (I-Ex/I-LE) appear to be much more dependent on the nature of the anion than are the rates of exciplex formation and decay,,,although the excited state data do not provide a quantitative measure of the anion effect on the C-O equilibrium. The detivation energies associated with exciplex formation in THF are calculated, to be 0.08 to 0.15 eV lower than for the, neutral amine; N,N-dimethyt-3-(1-pyrenyl)propan-1-amine. Decay of the exciplexes formed from the deprotonation of PyS is, hypothesized to occur through charge-recombination processes. To our knowledge, this is the first example in which photoacidity and intramolecular exciplex formation (i.e., a PCCT reaction) are coupled.
Subject: Photoinduced Electron-transfer
Editor: Amer Chemical Soc
Rights: fechado
Identifier DOI: 10.1021/acs.jpca.6b01519
Date Issue: 2016
Appears in Collections:Unicamp - Artigos e Outros Documentos

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