Two Key Descriptors for Designing Second Near-Infrared Dyes and Experimental Validation

Abstract

Second near-infrared (NIR-II) optical imaging technology has emerged as a powerful tool for diagnostic and image-guided surgery due to its higher imaging contrast. However, a general strategy for efficiently designing NIR-II organic molecules is still lacking, because NIR-II dyes are usually difficult to synthesize, which has impeded the rapid development of NIR-II bioprobes. Herein, based on the theoretical calculations on 62 multiaryl-pyrrole (MAP) systems with spectra ranging from the visible to the NIR-II region, a continuous red shift of the spectra toward the NIR-II region could be achieved by adjusting the type and site of substituents on the MAPs. Two descriptors (ΔE gs and μ gs ) were identified as exhibiting strong correlations with the maximum absorption/ emission wavelengths, and the descriptors could be used to predict the emission spectrum in the NIR-II region only if ΔE gs ≤ 2.5 eV and μ gs ≤ 22.55 D. The experimental absorption and emission spectra of ten MAPs fully confirmed the theoretical predictions, and biological imaging in vivo of newly designed MAP23-BBT showed high spatial resolution in the NIR-II region in deep tissue angiography. More importantly, both descriptors of ΔE gs and μ gs have shown general applicability to most of the reported donor−acceptor−donor-type non-MAP NIR-II dyes. These results have broad implications for the efficient design of NIR-II dyes.

Host–guest interaction induced room-temperature phosphorescence enhancement of organic dyes: a computational study

“…Radiative decay, non-radiative decay and ISC are three key decay processes that determine phosphorescent efficiency. The radiative rate constant ( k P ) of phosphorescence is estimated from the Einstein radiative relationship: k P = f T 1 –S 0 Δ E T 1 –S 0 2 /1.499 for a two-level system, 54,55 where f T 1 –S 0 is the oscillator strength and Δ E T 1 –S 0 is the vertical excitation energy of T 1 → S 0 based on the T 1 -geometry, in units of cm −1 . It is found that the k P of PYCl and PYBr are similar, but they are much smaller than those of host–guest complexes (Fig.…”