Ultrabright Dibenzofluoran-Based Polymer Dots with NIR-IIa Emission Maxima and Unusual Large Stokes Shifts for 3D Rotational Stereo Imaging.

Emerging organic molecules with emissions in the NIR-II region are garnering significant attention. Unfortunately, achieving accountable organic emission intensity over the NIR-IIa (1300 nm) region faces challenges due to the intrinsic energy gap law. Up to current stage, all reported organic NIR-IIa emitters belong to polymethine-based dyes with small Stokes shifts (< 50 nm) and low quantum yield (≤ 0.015%). However, such polymethines have proved to cause self-absorption with constrained emission brightness, limiting advanced development in deep-tissue imaging. Here we design a new NIR-IIa scaffold based on rigid and highly conjugated dibenzofluoran core terminated by amino-containing moieties that reveal emission peaks of 1230-1305 nm. The quantum yield is at least 10 times higher than all synthesized or reported NIR-IIa polymethines (Figure 1) with extraordinarily large Stokes shifts of 370-446 nm. DBF-BJ was further prepared as a polymer dot to demonstrate its in vivo 3D stereo imaging of mouse vasculature with a 1400 nm long-pass filter. This article is protected by copyright. All rights reserved.