Synthesis And Characterization Of Coumarin-Rhodamine Energy Transfer Cassettes And Their Spectral Properties

Fluorescent organic dyes have been widely used as fluorescent probes, labels logic gates, or regarded as potential candidates for applications in advanced materials, such as organic light-emitting diodes, and light harvesting systems. However, the application of various fluorophores is severely limited by the undesirable photophysical properties of various fluorophores. For instance, many bright organic dyes including rhodamine, fluorescein, Bodipy, and cyanine derivatives have the fatal disadvantage of very small Stokes shifts (typically less than 25 nm), which can lead to serious self-quenching and fluorescence detection error due to excitation backscattering effects. Therefore, it is critical to develop new dyes with predominant photophysical properties. Since it is still very difficult to rationally design and synthesis single organic dyes with predominant photophysical properties, recently, considerable attention has been paid toward the exploration of multi-fluorophores with energy donor-acceptor architectures. Hence, some energy-donor-acceptor architectures based on fluorescence resonance energy transfer(FRET) have been developed. Fluorescence resonance energy transfer (FRET) is a process of energy transfer, which occus throng remote dipole-dipole interaction between the energy of the donor and acceptor as well as space, also known as long distance energy transfer. FRET dyads are usually linked by a non-conjugated spacer, and the energy transfer occurs through space. FRET-based cassettes are still constrained by the requirement that the donor emission must have satisfactory overlap with the acceptor absorption, which essentially limits the pseudo-Stokes shifts and emission wavelength shift between donor and acceptor of FRET based systems.The laboratory is familiar with the synthesis of coumarin and rhodamine dyes and the spectral characteristics of these two dyes. With such conditions, we first designed and synthesized four new dyes. The first-generation coumarin-rhodamine TBET cassettes were constructed through a conjugated phenyl linker, which prevents the donor and acceptor moieties from becoming planar. In this paper, we present novel conjugated coumarin-rhodamine TBET cassettes. TBET cassettes may have more predominant photophysical properties, such as much larger pseudo-Stokes shifts and huger emission.We have been woked on the synthesis and characterization of target coumarin rhodamine molecules and studied the spectral properties. We found that the new TBET cassettes with remarkable pseudo-Stokes shifts up to 230 nm and prominent wavelength shifts between the donor and acceptor (up to 172 nm). The energy transfer efficiencies were almost 100%. The fluorescence enhancement factors (FEF) are 5.8,6.0,4.3,6.7-fold for cassettes 4a-d when compared to acceptor 6, respectively. With huge wavelength shifts (between the coumarin donor and rhodamine acceptor), these cassettes have potential application to development of powerful ratiometric fluorescence probes with large emission intensity ratios for useful applications in many field.