Design, Synthesis, And Applications Of Multichromophoric FRET Systems Based On Coumarin-Rhodamine

Fluorescence resonance energy transfer (FRET) is a nonradiative process whereby an excited state energy donor transfers energy to a proximal ground state energy acceptor through long-range dipole-dipole interactions. FRET plays a key role in the design of organic fluorescent dyes, small-molecue fluorescent probes and light-harvesting antenna molecules. Appropriate pair of energy donor and acceptor is the core part in the designing of FRET system. In this contribution, we synthesized several FRET moleculars by employing the excellent photophysical and photochemical properties of Coumarin, BODIPY and Rhodamine fluorophores, following several works have been performed.Firstly, we synthesized the4,5-carboxyl acid Rhodamine B isomers containing two carboxyl groups in the bottom ring of Rhodamine, which can be used to design Rhodamine-based FRET system for probe development by introducing energy donor and analyte-responsive reaction site, or design multichromophoric architectures to behave as light-harvesting antenna moleculars for application in solar energy conversion devices.Secondly, we synthesized two light-harvesting antenna moleculars CRB1and CRB2, which coumarin and BODIPY were connected to4(or5) and2-carboxyl acid through rigid piperazine linking, respectively. This antenna moleculars not only has strong absorption properties of Coumarin, BODIPY and Rhodamine fluorophore, but also makes up the defect of the single fluorophore absorption band which is narrow. The absorption spectrum of CRB1and CRB2antenna moleculars have covering300nm-650nm. It has a larger molar extinction coefficient, good solubility and strong light harvesting capability. Furthermore, the excitation energy transfer efficiency from the blue Coumarin and green BODIPY donor to the red Rhodamine receptor is nearly100%. These advantages show that the practical value of using Coumarin-Rhodamine-BODIPY energy transfer cassettes as light-harvesting antenna moleculars is very large.Thirdly, we developed a novel fluorescent turn-on thiol probe based on Coumarin-Rhodamine energy transfer cassettes. This probe employed the displacement method, in which the dye-ligand-metal ion "ensemble" is nonfluorescent due to paramagnetic Cu2+-induced fluorescence quenching. However, the addition of thiols released the ring-closed Coumarin-Rhodamine dye in to the solution with revival of fluorescence of Coumarin. Under normal physiological conditions, the probe has a highly selective for biological thiols such as GSH, Cys and Hcy. Furthermore, the probe can measure the turnable range of biothiols by changing the concentration of Cu2+...