Donor-conformation-dependent energy transfer for dual-color fluorescent probe with high-resolution imaging

Herein,we presented a brand-new concept to construct the Forster resonance energy transfer(FRET)based cassette by integrating a vibration-induced emission(VIE)chromophore as the donor.Different from traditional donors only with a single emission,the VIE donor possessed well-separated dual emission bands by altering the excited state molecular configuration from the bent state to the planar state.By linking an acceptor such as a cyanine dye(Cy5),a novel VIE-FRET cassette(PPCy5)was prepared.The planar emission profile of the VIE donor moiety could fully cover the absorption of Cy5,and thus the complete FRET process enabled the excellent bimodal spectra difference of 142 nm and ultra-large pseudo-Stokes shift of up to 300 nm.Benefiting from the viscosity-dependent characteristic of the VIE donor,PPCy5 could clearly and intuitively reveal the different viscosity regions in vivo by dual-color and high-resolution imaging.The VIE-FRET paradigm provides an optional platform for developing donor-acceptor-based dual-color fluorescent probes with high-resolution imaging ability.