Selective Triplet–Singlet Foerster-Resonance Energy Transfer for Bright Red Afterglow Emission

摘要

Foerster-resonance energy transfer (FRET_(T-S)) from the lowest excited tripletstate (T_1) of a donating sensitizer to a fluorescence acceptor can be used toobtain bright room-temperature afterglow emission at long wavelengths.However, the energy transfer from the lowest excited singlet state of thedonor to the acceptor is an undesirable deactivation pathway that preventsFRET_(T-S). Herein, heteroatoms in chromophores are shown to allow selectiveand efficient FRET_(T-S) for enhanced triplet emission for bright roomtemperatureafterglow emission at long wavelengths. Different transitioncharacteristics between the lowest singlet excited state and triplet states inheteroatom-containing chromophores accelerate triplet generation, enablingnear-zero fluorescence yields. Out-of-plane vibrations of the heteroatoms inaromatic fused rings greatly enhance the radiative rate from T_1 by a factor of88 relative to non-heteroatom-containing fused chromophore. The compatibilityof the near-zero fluorescence and the enhanced triplet emission in aheteroatom-containing fused chromophore enable selective and efficientFRET_(T-S) pathways, resulting in room-temperature red afterglow emission witha yield of 17%. The bright emission at long-wavelengths allows distinguishable,multiple spectral signals in ambient white light.