よく光る蛍光色素の分子設計

Abstract

Recently, much attention has been focused on organic fluorescent dyes with a high absorption coefficient and high fluorescent quantum yield, with the aim of using them in fascinating applications, for example, in organic electroluminescence and molecular imaging and as sensors and probes. In 1951, Prof. Zen-ichi Yoshida (Kyoto University) published certain requirements, which are of great significance, for the design of highly fluorescent dyes (Yoshida’s fluorescence rules) in this journal (J. Synth. Org. Chem., Jpn., 9, 230 (1951)). Currently, several modern techniques are available for investigating photophysical processes; therefore, it is necessary to establish sophisticated processes and guidelines for dye design. This review would serve as a guide for the design of highly fluorescent dyes. First, the significance of linear π-extension of aromatic or carbon-carbon multibonds and π-extension of polycyclic aromatic compounds for the synthesis of highly luminescent dyes is emphasized. Second, a Jablonski diagram describing a photophysical process is presented. Two important processes—intersystem crossing and internal conversion—play notable roles in fluorescence enhancement. Third, florescent dyes based on intramolecular charge-transfer complexes are described. Furthermore, a case study on the structure-photoluminescence property relationship for pyrene carbonyl dyes (pyrene with aldehyde, ketone, carboxylic acid, ester, and dialkylamide groups) is presented. The photophysical properties of pyrene modified by carbonyl substituents are successfully revised and systematized by measuring the absolute fluorescence quantum yield in various solvents and by performing density functional theory (DFT) calculations. Moreover, it is demonstrated that the photoluminescence properties of such compounds can be predicted on the basis of TD-DFT calculations.