Through‐Bond Energy Transfer Cassettes with Minimal Spectral Overlap between the Donor Emission and Acceptor Absorption: Coumarin–Rhodamine Dyads with Large Pseudo‐Stokes Shifts and Emission Shifts

Abstract

Small-molecule organic dyes have been widely used in fluorescent probes, [1] labels, [2] logic gates, [3] light-emitting materials, [4] and light-harvesting systems. [5] However, the undesirable photophysical properties of various fluorophores still constrain the full potential of their applications. For instance, many bright organic dyes including rhodamine, fluorescein, boron dipyrromethane (BODIPY), and cyanine derivatives have the serious disadvantage of very small Stokes shifts (typically less than 25 nm), which can lead to serious self-quenching and fluorescence detection errors because of excitation backscattering effects.[6] Therefore, there is a need to develop dyes with improved properties.Since it is still difficult to judiciously design single organic dyes with desirable photophysical properties, considerable attention has recently been paid to the exploration of multifluorophores with energy-donor-acceptor architectures. [1m, 6b, 7-9] In this regard, some energy-donor-acceptor systems based on fluorescence resonance energy transfer (FRET) have been constructed. [6b, 8] FRET dyads are usually linked by a nonconjugated spacer, and the energy transfer occurs through space. Although the pseudo-Stokes shifts (the wavelength discrepancy between the donor absorption and the acceptor emission in an energy transfer system with almost 100 % energy transfer efficiency [7] ) of FRET-based energy cassettes are larger than the Stokes shifts of either the donor or acceptor dyes, FRET-based cassettes are still limited by the requirement that the donor emission must have strong overlap with the acceptor absorption.[10] This requirement essentially restricts the pseudo-Stokes shifts as well as the emission shifts (the emission wavelength shift between the donor and acceptor) of FRET-based systems. Like the pseudo-Stokes shift, the emission shift is also an important parameter in energy-transfer dyads. A large emission shift in energy transfer systems should result in two well-separated emission peaks, which is favorable for the precise measurement of the peak intensities and ratios.[6b, 11] Thus, energytransfer dyads with large pseudo-Stokes shifts and emission shifts are desirable.By contrast, through-bond energy transfer (TBET) is theoretically not subjected to the constraint of intense spectral overlap between the donor emission and the acceptor absorption.[9] Thus, TBET cassettes may have large pseudoStokes shifts and emission shifts. Unlike through-space energy-transfer cassettes, in TBET cassettes, the donor and the acceptor units are joined by a conjugated spacer. Burgess and co-workers have developed elegant TBET systems based on the conjugated fluorescein-rhodamine system. [9a,b] However, the fluorescein (donor) emission overlaps significantly with the rhodamine (acceptor) absorption and the advantage of TBET, that is, no requirement of strong spectral overlap between the donor emission and the acceptor absorption, was not really capitalized upon in these conjugated fluoresceinrhodamine energy transfer ...

Naked oats-derived dual-emission carbon nanodots for ratiometric sensing and cellular imaging

“…A lot of researchers have made an intense effort for the development of ratiometric pH probes. Toward this end, various design strategies based on intramolecular charge transfer (ICT) [47], Förster resonance energy transfer (FRET) [48], through bond energy transfer (TBET) [49] or other approach [50] have been employed to devise a wide variety of dual-emission or excitation ratiometric fluorescent pH probes with either favorable emission or excitation spectral properties. Despite these efforts, ratiometric probes that can selectively detect protons in aqueous solutions with well-resolved dual emission peaks (emission shift > 80 nm) are very rare.…”

A Dual Colorimetric/Fluorescence System for Determining pH Based on the Nucleophilic Addition Reaction of an o‐Hydroxymerocyanine Dye

“…[1][2][3][4] Dyes, including rhodamine, fluorescein, cyanine, coumarin, naphthalimide, and BODIPY,h ave been employedi no ptical pH probes. [5][6][7][8][9][10][11][12][13][14][15][16] The strategies employedf or designing these probesh avet hus far been mainly basedo nt wo philosophies. In the first approach, an amine nitrogena tom is utilizeda sacenter for reversible protonation to establish an equilibrium between free amine and quaternary ammonium salt forms.…”

A Ratiometric Fluorescent Probe Based on a Through‐Bond Energy Transfer (TBET) System for Imaging HOCl in Living Cells

“…However,t heir applications were limited because of small Stokess hifts and interference fromt he environment, probec oncentration, and excitation intensity. [26][27][28][29][30][31][32][33][34] Ratiometric probes based on fluorescence resonance energy transfer (FRET)c an give as olution to the tissues, becauset hey not only possessl arger pseudo-Stokes shifts,b ut also have ar ecorded ratio signal of two emission intensities at different wavelength, which can afford ab uilt-in correction. Normally,t he donor and the acceptori nF RET sensors are usually linked with an onconjugateds pacer,a nd the energyt ransfers from the donor to the acceptor through space.…”

“…[27,[35][36][37][38] As ubstantial spectral overlap is necessary betweent he donore mission band and the acceptora bsorption band,w hich sometimes limits the choice andt he design of FRET sensors. [34] In contrast, for aT BET (through-bond energy transfer) system to be effective, the donor and the acceptor are linked with an electronically conjugatedb ond, through which the energy can transfer from the donor to acceptor without the need for as ubstantial spectralo verlap between the donor emission and acceptora bsorbance. [39] These can afford the desired flexibility in the choice of fluorophore and the large emission shifts between the two emission peaks.…”