The simultaneous pursuit of accelerative radiative and restricted nonradiative decay is of tremendous significance to construct high-luminescence-efficiency fluorophores in the second near-infrared wavelength window (NIR-II), which is seriously hindered by the energy gap laws. Herein, a mash-up strategy of π-extension and deuteration is proposed to efficaciously ameliorate the knotty problem. By extending the π-conjugation of the aromatic fragment and introducing an isotope effect to the aggregation-induced emission luminogen (AIEgen), an improved oscillator strength (f), coupled with suppressed deformation and high-frequency oscillation in the excited state, are successively implemented. In this case, a faster rate of radiative decay (kr) and restricted nonradiative decay (knr) are simultaneously achieved. Moreover, the preeminent emissive property of AIEgen in the molecular state could be commendably inherited by the aggregates. The corresponding NIR-II emissive AIEgen-based nanoparticles display high brightness, large Stokes shift, and superior photostability simultaneously, which can be applied for image-guided cancer and sentinel lymph node (SLN) surgery. This work thus provides a rational roadmap to improve the luminescence efficiency of NIR-II fluorophores for biomedical applications.
Keywords: NIR-II fluorescence; aggregation-induced emission; image-guided surgery; intramolecular motion; radiative and nonradiative decay.