Singlet Exciplexes between a Thioxanthone Derivative and Substituted Aromatic Quenchers: Role of the Resonance Integral

Abstract

Fluorescence quenching of a thioxanthone derivative by methyl- and methoxy-substituted benzenes (MeB and MeOB, respectively) is performed in solvents of different polarity. Emissive exciplexes are observed even in polar solvents and provide kinetic and spectroscopic data over a large scale of solvent polarity. These data were subsequently analyzed by use of a new theoretical model that leads to a thermodynamic relationship between exciplex and electron-transfer driving forces Delta G(exc) and Delta G(et), respectively. The remarkable agreement found between this model and both kinetic and spectroscopic data supports its validity. Moreover, the difference observed between MeB and MeOB compounds in quenching efficiency is analyzed by this model and provides the main parameters governing exciplex features, especially the resonance integral between locally excited and charge-transfer states.

Electron Transfer in Supercritical Carbon Dioxide: Ultraexothermic Charge Recombination at the End of the “Inverted Region”

“…Similar results were obtained with the other aromatic hydrocarbons studied in this work. The degree of charge transfer in this species can be experimentally assessed from the variation of the exciplex emission maximum (ñ ex ) with the polarity of the solvent, [17] and from the separation between ñ ex and the 0,0 transition of the corresponding monomer (ñ m ). [18] According to the Lippert-Mataga relationship, [19,20] ñ ex is determined by the dipole moment of the exciplex (m) in a solvent of dielectric constant e and refractive index n [Eq.…”

Bimolecular photoinduced electron transfer in non-polar solvents beyond the diffusion limit

“…This idea was proposed by several authors to account the unexpectedly large quenching rate constants measured around ∆G ET = 0. 6,9,54,66 These authors suggested that, in this case, quenching occurs adiabatically and results in the formation of an exciplex. However, such mechanism was not invoked for more exergonic ET.…”

“…5,51,52 Interestingly, a) Electronic mail: eric.vauthey@unige.ch unexpectedly large quenching rate constants where observed even at negative ET driving forces (∆G ET > 0). 53,54 This was explained by the stabilisation energy associated with exciplex formation that is not included when calculating ∆G ET according to the conventional Weller equation. Additionally, the authors suggested that, in this case, the coupling between the reactants is so large that ET is an adiabatic process, and is thus distinct from the non-adiabatic ET discussed in Marcus theory.…”

Photoinitiation mechanism of free radical photopolymerization in the presence of cyclic acetals and related compounds

“…As indicated in Table 6, the E ox of BDA, BDO, PA, and MDN result in slightly positive Δ G et values. The Δ G et of BDO and PA can ensure high quenching rate constants when an exciplex is involved 36, 38. For BDA, the higher Δ G et (+0.37 eV) supports the fact that the 3 BP/BDA is not efficient.…”