An exciplex mechanism for the quenching of singlet excited states of aliphatic ketones by carbon tetrachloride

Abstract

RAFIK 0. LOUTFY and ALLAN C. SOMERSALL. Can. J. Chem. 54, 760 (1976). Non-classical energy transfer from the excited singlet states of aliphatic ketones to carbon tetrachloride leads to sensitized decomposition products and fluorescence quenching. The correlation of the ionization potentials for a wide variety of such ketones with the corresponding quenching constants from fluorescence data has been rationalized by an exciplex mechanism. The correlation implies that charge transfer from the excited ketone to the carbon tetrachloride is a major contribution to the exciplex state for which two possible structures are tentatively proposed. The quenching of fluorescence by lnolecules which cannot function by classical electronic energy transfer has been the focus of many investigations in recent years. A considerable body of evidence has given direct support for formation of excited-state complexes in many such systems (1).Halogenated alkanes (2), dienes (3), and amines (4) where IPD is the ionization potential of the donor, EAA is the electron affinity of the acceptor, Cis the coulomb energy, and P is the polarization energy of the separated charges. E, represents the energy of the first excited state. Generally, for a common fluorescent donor and a series of different electron-deficient quenchers, the bimolecular rate constants can be correlated with the corresponding EA values of the quenchers. Other correlations have sometimes been made for different fluophores and a single quencher but both IP and E, values change simultaneously in the series of aromatics which have been reported so that k,, had to be correlated with -Es). We wish to report some linear free energy correlations for the fluorescence quenching of a wide variety of aliphatic ketones by carbon tetrachloride which affords some insight into the exciplex intermediate in this system (5). The quenching of the singlet excitation of aliphatic ketones by a common quencher affords a rather unique system where E, proves to be practically , constant while IP varies significantly.The photochemistry of ketones in carbon tetrachloride has been reported earlier (5). The Can. J. Chem. Downloaded from www.nrcresearchpress.com by 34.218.44.141 on 05/11/18For personal use only.

One-electron photooxidation of carbazole in the presence of carbon tetrachloride. Part I. Carbon tetrachloride and ethanol used as reaction media

“…The energy loss into the singlet state manifold may proceed through emission of radiation (reaction [2]) or radiationless processes via the external spin-orbital coupling with CCl, molecule, internal conversion (reaction [3]) or via complexation (reactions [4] and [5] 3 zole molecule show that among a variety of mesomeric structures of the radical-cation, the l , 3 , 6 , 8 , and 9(N) positions are likely to be favored (1 1, 12).…”

“…commonly connected with the photochemical reacCarbon tetrachloride is a well-known fluorestion in which CC14 participates as an electron cence quencher of various aromatic electron do-acceptor, favorable conditions being created by the nors (1)(2)(3)(4)(5)(6). The mechanism of quenching is most distinctive electron affinity of CCl, (2.12 eV) (7) and comparatively low C-Cl bond energy (23 1.2 kJ 'On leave from the Department of Chemistry, University of mol-') (8).…”

Analysis of 2-Phenoxyaniline Fluorescence Quenching by Chloromethanes

“…Molecular interactions are taken for the analysis of quenching results with two different models (i) stern Volmer plots (ii) Smoluchowski-type quenching model [5][6][7]. Fluorescence quenching of aromatic hydrocarbons by haloalkanes was studied [7][8][9][10][11][12][13][14]. When the overlap of donor emission and acceptor absorption is negligible, quenching was justified in terms of a non-emissive exciplex [9] and its formation can only be inferred and not observed [15].…”

One-electron photooxidation of N-ethylcarbazole in the presence of carbon tetrachloride. Products and mechanism of the photochemical reaction

“…Carbon tetrachloride is well known to be an efficient fluorescence quencher of a large variety of organic molecules (1,2,(26)(27)(28)(29)(30)(31)(32). The fluorescence quenching process has usually been explained by the exciplex formation between the singlet excited molecule and the CCI, molecule.…”