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. 2023 Jan 29;28(3):1287.
doi: 10.3390/molecules28031287.

Acid-Triggered Switchable Near-Infrared/Shortwave Infrared Absorption and Emission of Indolizine-BODIPY Dyes

Matthew A Saucier  1 , Cameron Smith  1 , Nicholas A Kruse  1 , Nathan I Hammer  1 , Jared H Delcamp  1   2   3
Affiliations

Acid-Triggered Switchable Near-Infrared/Shortwave Infrared Absorption and Emission of Indolizine-BODIPY Dyes

Matthew A Saucier et al. Molecules. .

Abstract

Fluorescent organic dyes that absorb and emit in the near-infrared (NIR, 700-1000 nm) and shortwave infrared (SWIR, 1000-1700 nm) regions have the potential to produce noninvasive high-contrast biological images and videos. BODIPY dyes are well known for their high quantum yields in the visible energy region. To tune these chromophores to the NIR region, fused nitrogen-based heterocyclic indolizine donors were added to a BODIPY scaffold. The indolizine BODIPY dyes were synthesized via microwave-assisted Knoevenagel condensation with indolizine aldehydes. The non-protonated dyes showed NIR absorption and emission at longer wavelengths than an aniline benchmark. Protonation of the dyes produced a dramatic 0.35 eV bathochromic shift (230 nm shift from 797 nm to 1027 nm) to give a SWIR absorption and emission (λmaxemis = 1061 nm). Deprotonation demonstrates that material emission is reversibly switchable between the NIR and SWIR.

Keywords: BODIPY; fluorescence imaging agents; indolizine; near-infrared (NIR) emission; shortwave infrared (SWIR) emission.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Previously published BODIPY dyes [12,28,29] and novel indolizine-BODIPY dyes organized by peak emission wavelength (λmaxemis).
Figure 2
Figure 2
HOMO (bottom) and LUMO (top) orbitals for the three BODIPY dyes (DMA, 2Ph, and 1Ph).
Scheme 1
Scheme 1
Synthetic approach to access indolizine BODIPY dyes.
Figure 3
Figure 3
Photophysical studies of BODIPY dyes: (a) Absorption (solid line) and emission (dashed line) of neutral dyes DMA, 2Ph, and 1Ph in CH2Cl2; (b) Absorption (solid line) of protonated dyes DMA-TFA, 2Ph-TFA, 1Ph-TFA, and emission (dashed line) of 1Ph-TFA in CH2Cl2. (c) Reversible protonation observed in the absorption curves of 1Ph, 1Ph-TFA, and 1Ph-TFA-TEA in DMSO-d6. (d) Photographs of the solutions used in graph (c).
Figure 4
Figure 4
(a) Transformation of 1Ph after treatment with TFA with a plausible structure of protonated dye 1Ph-TFA; (b) HOMO (left) and LUMO (right) orbitals for 1Ph-TFA in (a).
See this image and copyright information in PMC

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