Structure-reactivity factors in the quenching of fluorescence from naphthalenes by conjugated dienes

Singlet excited state rate constants have been measured for both the heterolytic and homolytic photocleavage of 3- and 4-methoxy and 3- and 4-cyano (1-naphthylmethyl)trimethylammonium chlorides, 6–10. The results are interpreted in terms of the meta effect or changes in charge distribution upon excitation and the competition between bond cleavage, electron transfer, and hydrogen atom transfer in the contact pairs resulting from the two types of cleavage.

Section: Preparative Scale Photolysis Of the Salts 7-10supporting

confidence: 60%

Substituent effects on homolytic versus heterolytic photocleavage of (1-naphthylmethyl)trimethylammonium chlorides

Foster¹,

Gaillard²,

Mathur³

et al. 1987

“…The observation of fluorescence quenching in such cases where there is negligible overlap of donor emission and acceptor absorption spectra (required for classical transfer) was rationalized by ~a m m o n d and co-workers (3) 'This is consistent with the definition proposed formally by J. B. Birks: "An exciplex is an electronically excited atomic or molecular complex of definite stoichiometry, which is dissociated in its electronic ground state" in ref.…”

supporting

confidence: 65%

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

Loutfy¹,

Somersall²

1976

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.

“…Some of the processes given above may be neglected for various reasons: (i) The extent of isomer formation process [6] is not appreciable under the experimental conditions used here and may be neglected in comparison to the much more rapid processes of intersystem crossover and fluorescence (13). (ii) None of the benzene -halogenated alkane systems examined exhibited any emission other than the fluorescence of benzene molecule.…”

Section: A Singlet-state Quenchingmentioning

confidence: 99%

Quenching of the singlet and triplet state of benzene by halogenated alkanes in the vapor phase

Khwaja¹,

Semeluk²,

Unger³

1982

. 60, 1767 (1982).The second order rateconstants (k,) for the quenching of the singlet state of benzene by several halogenated alkanes (viz. CH,Br2, CCI,, CH3CC13, CHCI,, CHF,, CH,CI, CH3F, CH2F2, CH2C12, CFCI,, CF2CI2, CF,CI, CF,) in the vapor phase have been measured. For CCl,, CHCI,, CH2C12, and CH,CI, which were previously studied by Das Gupta and Phillips, there is satisfactory agreement between the k, values obtained in the separate investigations. The linear dependence of the electron affinity of quencher with the corresponding quenching rate constants supports an exciplex mechanism in accordance with Klein's model. Charge transfer occurs from benzene to halogenated alkane and is greater for the chloro alkanes than for mixed fluoro-chloro alkanes. In the case of the triplet state of benzene, whose behaviour was monitored using the sensitized emission of biacetyl technique, quenching effects were at best one order of magnitude smaller and probably involve more than one bimolecular process.