Fluorescence methods are being used increasingly in biochemical, medical, and chemical research. This is because of the inherent sensitivity of this technique. and the favorable time scale of the phenomenon of fluorescence. 8 Fluorescence emission occurs about 10- sec (10 nsec) after light absorp tion. During this period of time a wide range of molecular processes can occur, and these can effect the spectral characteristics of the fluorescent compound. This combination of sensitivity and a favorable time scale allows fluorescence methods to be generally useful for studies of proteins and membranes and their interactions with other macromolecules. This book describes the fundamental aspects of fluorescence. and the biochemical applications of this methodology. Each chapter starts with the -theoreticalbasis of each phenomenon of fluorescence, followed by examples which illustrate the use of the phenomenon in the study of biochemical problems. The book contains numerous figures. It is felt that such graphical presentations contribute to pleasurable reading and increased understand ing. Separate chapters are devoted to fluorescence polarization, lifetimes, quenching, energy transfer, solvent effects, and excited state reactions. To enhance the usefulness of this work as a textbook, problems are included which illustrate the concepts described in each chapter. Furthermore, a separate chapter is devoted to the instrumentation used in fluorescence spectroscopy. This chapter will be especially valuable for those perform ing or contemplating fluorescence measurements. Such measurements are easily compromised by failure to consider a number of simple principles."

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Principles of fluorescence spectroscopy

Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment

For more than 70 years, researchers in several areas of science have been intrigued by the physical and chemical properties of the lowest excited states of molecular oxygen. With two singlet states lying close above its triplet ground state, the O2 molecule possesses a very unique configuration, which gives rise to a very rich and easily accessible chemistry, and also to a number of important photophysical interactions. In particular, photosensitized reactions of the first excited state, O2(∆g), play a key role in many natural photochemical and photobiological processes, such as photodegradation and aging processes including even photocarcinogenesis. Reactions of O2(∆g) are associated with significant applications in several fields, including organic synthesis, bleaching processes, and, most importantly, the photodynamic therapy of cancer, which has now obtained regulatory approval in most countries for the treatment of several types of tumors. The development of both applications and novel observation techniques has strongly accelerated during the past few years. Significant recent advances include, for example, the development of novel luminescent singlet oxygen probes,1-4 the time-resolved detection of O2(∆g) in a transmission microscope,5 the first time-resolved measurements of singlet oxygen luminescence in vivo,6 and the observation of oxygen quenching of triplet-excited single molecules.7 Experimental and theoretical studies on the mechanisms of photosensitized formation of excited O2 states and of their deactivation have been performed for almost 40 years. While most early liquid-phase studies were exclusively concerned with O2(∆g), recent technological advances also made possible time-resolved investigations of the second excited state, O2(Σg), which can be formed in competition with O2(∆g) in many cases. A significant number of * Corresponding author. Tel.: ++49 69 79829448. Fax: ++49 69 79829445. E-mail: R.Schmidt@chemie.uni-frankfurt.de. 1685 Chem. Rev. 2003, 103, 1685−1757

Physical mechanisms of generation and deactivation of singlet oxygen.

On the design of highly luminescent lanthanide complexes

Thermally activated delayed fluorescence (TADF) emitters, which produce light by harvesting both singlet and triplet excitons without noble metals, are emerging as next-generation organic electroluminescent materials. In the past few years, there have been rapid advances in molecular design criteria, our understanding of the photophysics underlying TADF and the applications of TADF materials as emitters in organic light-emitting diodes (OLEDs). This topic is set to remain at the forefront of research in optoelectronic organic materials for the foreseeable future. In this Review, we focus on state-of-the-art materials design and understanding of the photophysical processes, which are being leveraged to optimize the performance of OLED devices. Notably, we also appraise dendritic and polymeric TADF emitters — macromolecular materials that offer the potential advantages of low cost, solution processable and large-area OLED fabrication. Thermally activated delayed fluorescence (TADF) emitters are promising electroluminescent materials for next-generation organic light-emitting diodes (OLEDs). In this Review, the molecular design, photophysical characteristics and OLEDs composed of small-molecule, dendritic and polymeric TADF emitters are discussed.

All-organic thermally activated delayed fluorescence materials for organic light-emitting diodes

The fluorescence quenching mechanism in a highly exothermic region of the Rehm-Weller relationship is shown to be a long-distance electron transfer for producing the geminate radical ion pair with fluorescer radical cation in an electronically excited state and quencher radical anion in the ground state

Quenching mechanism in a highly exothermic region of the Rehm-Weller relationship for electron-transfer fluorescence quenching

Dependence of the fluorescence-quenching rate constant k q , effective quenching distance r q , and free radical yield Φ R on the free enthalpy change ΔG f of full electron transfer has been studied in dichloromethane by using anthracenecarbonitriles as electron-accepting fluorescers and amino- and methoxybenzenes as electron-donating quenchers. On the basis of the present data in dichloromethane and the previous data in acetonitrile, the solvent effects on the electron-transfer fluorescence-quenching mechanism and on the back electron-transfer reaction within the geminate radical ion pairs are elucidated

Solvent effects on photoinduced electron-transfer reactions

Evidence of exciplex formation in acetonitrile

Four kinds of evidence for exciplex formation in acetonitrile are summarized. They indicate that the fluorescence quenching mechanism of an electron donor-acceptor system depends on (i) effective quenching distance and (ii) free-enthalpy change of actual electron transfer in addition to (iii) solvent polarity. It is shown that the Rehm-Weller relationship (and the lack of an inverted region in it) is interpreted by taking into account both (i) and (ii). A criterion for determining the quenching mechanism in a highly exothermic region is proposed.

A new aspect of photoinduced electron transfer in acetonitrile

Rate constants for quenching of several triplets by ferrocene have been determined in ethanol. Most triplets have been found to be deactivated by ferrocene, yielding no observable transient absorption. The rate constant increases with increasing triplet energy in the range 8000–17000 cm−1. The quenching mechanism has been discussed, the lowest triplet level of ferrocene being estimated to be 15000±1000 cm−1.

Koichi Kikuchi

Papers

Quenching mechanism in a highly exothermic region of the Rehm-Weller relationship for electron-transfer fluorescence quenching

Solvent effects on photoinduced electron-transfer reactions

Evidence of exciplex formation in acetonitrile

A new aspect of photoinduced electron transfer in acetonitrile

A Study of Quenching of Triplets by Ferrocene