Charge‐Transfer Complex and Solvent‐Shared Ion Pair in Fluorescence Quenching
01 Aug 1967-Journal of Chemical Physics (American Institute of Physics)-Vol. 47, Iss: 3, pp 1184-1185
About: This article is published in Journal of Chemical Physics.The article was published on 1967-08-01. It has received 159 citations till now. The article focuses on the topics: Quenching (fluorescence) & Resonance fluorescence.
TL;DR: In this article, the rate constants of 60 typical electron donor-acceptor systems have been measured in de-oxygenated acetonitrile and are shown to be correlated with the free enthalpy change, ΔG23, involved in the actual electron transfer process.
Abstract: Fluorescence quenching rate constants, kq, ranging from 106 to 2 × 1010 M−1 sec−1, of more than 60 typical electron donor-acceptor systems have been measured in de-oxygenated acetonitrile and are shown to be correlated with the free enthalpy change, ΔG23, involved in the actual electron transfer process in the encounter complex and varying between + 5 and −60 kcal/mole. The correlation which is based on the mechanism of adiabatic outer-sphere electron transfer requires ΔG≠23, the activation free enthalpy of this process to be a monotonous function of ΔG23 and allows the calculation of rate constants of electron transfer quenching from spectroscopic and electrochemical data. A detailed study of some systems where the calculated quenching constants differ from the experimental ones by several orders of magnitude revealed that the quenching mechanism operative in these cases was hydrogen-atom rather than electron transfer. The conditions under which these different mechanisms apply and their consequences are discussed.
TL;DR: A cross-disciplinary review of the essential characteristics of excitons in nanoscience is presented, highlighting the importance of quantum dots, conjugated polymers, carbon nanotubes and photosynthetic light-harvesting antenna complexes.
Abstract: Nanoscale systems are forecast to be a means of integrating desirable attributes of molecular and bulk regimes into easily processed materials. Notable examples include plastic light-emitting devices and organic solar cells, the operation of which hinge on the formation of electronic excited states, excitons, in complex nanostructured materials. The spectroscopy of nanoscale materials reveals details of their collective excited states, characterized by atoms or molecules working together to capture and redistribute excitation. What is special about excitons in nanometre-sized materials? Here we present a cross-disciplinary review of the essential characteristics of excitons in nanoscience. Topics covered include confinement effects, localization versus delocalization, exciton binding energy, exchange interactions and exciton fine structure, exciton-vibration coupling and dynamics of excitons. Important examples are presented in a commentary that overviews the present understanding of excitons in quantum dots, conjugated polymers, carbon nanotubes and photosynthetic light-harvesting antenna complexes.
TL;DR: In this paper, a number of examples of solvatochromic shifts are shown and discussed according to the various solute-medium interactions, and some limitations of the theories of solvent shifts and possible improvements are discussed.
Abstract: The displacement of electronic absorption and luminescence spectra (solvatochromic shifts) are related to the solute—medium interactions. These interactions can be non-specific (dielectric interactions) when they depend only on multiple and polarizability properties of the solute and solvent molecules; but specific associations such as hydrogen bonding can also be important. A number of examples of solvatochromic shifts are shown and discussed according to the various solute—medium interactions. The properties of solvent mixtures and those of rigid media are considered, as well as the “thermochromic shifts” which result from the change in the temperature of the medium. The use of solvatochromic shifts for the determination of the dipole moment and of the polarizability of electronically excited molecules has been important for an understanding of electron distribution changes in such states; examples of such determinations are given, together with references to the original literature. In the final section some limitations of the theories of solvent shifts and possible improvements are discussed.
TL;DR: In polar solvents, where most reactions are carried out, the primary intermediate is a geminate radical-ion pair, A•-/D•+ (eq 1).
Abstract: From the accumulated results of several research groups over the last 25 years, it is clear that photoinduced electron-transfer reactions have significantly broadened the scope of organic photochemistry.1 The fundamental mechanistic principle is that when quenching of an excited state via electron transfer is sufficiently exothermic, the reaction occurs at or close to the diffusion-controlled limit (kdiff). In polar solvents, where most reactions are carried out, the primary intermediate is a geminate radical-ion pair, A•-/D•+ (eq 1).3 Return electron transfer within the
TL;DR: A series of intramolecular triads with linear, rod-like structures has been developed that undergo very efficient two-step electron transfer following direct excitation of a chromophore possessing a charge transfer (CT) excited state as mentioned in this paper.
Abstract: A series of intramolecular triads with linear, rod-like structures has been developed that undergo very efficient two-step electron transfer following direct excitation of a chromophore possessing a charge transfer (CT) excited state. The CT state of 4-aminonaphthalene-1,8-imide (ANI), produced by direct excitation of the chromophore, has about 70% of a negative charge transferred from the amine to the imide. Attachment of aniline (An) and p-methoxyaniline (MeOAn) donors to ANI by means of a piperazine bridge results in linear dyads, An-ANI and MeOAn-ANI, that undergo rapid electron transfer in about 10-11 s to give a >99% yield of the ion pairs, An+-ANI- and MeOAn+-ANI-, in which the charges are separated by 7.7 A. The formation and decay of these ion pairs can be monitored directly by transient absorption spectroscopy. Further attachment of a 1,8:4,5-naphthalenediimide (NI) electron acceptor to the imide group of ANI using a 2,5-dimethylphenyl spacer results in triads An-ANI-NI and MeOAn-ANI-NI. Excitat...
••01 Oct 1963
TL;DR: In this paper, angeregten Molekulen and geeigneten Elektronendonatoren moglich, die im Grundzustand nicht stattfinden.
Abstract: Eine einfache Energiebetrachtung zeigt, das elektronenangeregte Molekule ein geringeres Ionisierungspotential und eine hohere Elektronenaffinitat besitzen als Molekule im Grundzustand. Dadurch sind Elektronenubertragungsreaktionen zwischen angeregten Molekulen und geeigneten Elektronendonatoren bzw. -akzeptoren moglich, die im Grundzustand nicht stattfinden. Dies wird durch blitzlichtspektroskopische Untersuchungen an Perylenlosungen (+ Amin bzw. Pyridinium) bestatigt. Die mit Hilfe von Fluoreszenzmessungen an den gleichen Systemen durchgefuhrte kinetische Untersuchung zeigt, das der Elektronenubergang in unpolaren Medien zu einem angeregten Elektronenuberfuhrungskomplex fuhrt, wahrend er in polaren Losungsmitteln offenbar auch ohne direkten Kontakt zwischen den Reaktionspartnern moglich ist.
TL;DR: In this paper, the Fluoreszenz-Abklingfunktionen of zwei Bis(iV-methyl-benzoxazol)-monomethincyaninen and von Perylen in Benzol-Dimethylanilin-Gemischen ließen sich in zwei, mit verschiedenen Zeitkonstanten einfach exponentiel! abklingende Komponenten zerlegen.
Abstract: Es wird eine Apparatur beschrieben, die Fluoreszenz-Abklingfunktionen mißt, deren mittlere Abklingzeiten zwischen 4 und 1000 nsec liegen. Die Anordnung kann auch zur Messung von Momentan-Spektren mit einem zeitlichen Auflösungsvermögen von 2 nsec verwendet werden. Der exponentielle Verlauf der Abklingfunktionen einiger Farbstoffe wurde über drei Dekaden quantitativ \\^erfolgt. Die Abklingfunktionen von zwei Bis(iV-methyl-benzoxazol)-monomethincyaninen und von Perylen in Benzol-Dimethylanilin-Gemischen ließen sich in zwei, mit verschiedenen Zeitkonstanten einfach exponentiel! abklingende Komponenten zerlegen. Die einzelnen Komponenten konnten bestimmten Molekülarten zugeordnet werden.