Photophysical Tuning of Shortwave Infrared Flavylium Heptamethine Dyes via Substituent Placement

Optical imaging in the shortwave infrared region (SWIR, 1000–2000 nm) provides high-resolution images in complex systems. Here we explore substituent placement on dimethylamino flavylium polymethine dyes, a class of SWIR fluorophores. We find that the position of the substituent significantly affects the λmax and fluorescence quantum yield. Quantum-mechanical calculations suggest that steric clashes control the extent of π-conjugation. These insights provide design principles for the development of fluorophores for enhanced SWIR imaging.