Structure–Property Relationships of Near-Infrared Cyanine Dyes: Chalcogen-Driven Singlet Oxygen Generation with High Fluorescence Efficiency

High Resolution Image Download MS PowerPoint Slide We report the design, synthesis, and optical characterisations of eight novel near-infrared (NIR) cyanine dyes incorporating different chalcogens (O, S, and Se). These dyes exhibited excellent deep-NIR absorption (λ max = 767–833 nm) and emission (λ max = 784–859 nm) profiles. TDDFT calculations matched well the experimental trends and data. All compounds exhibited high extinction coefficients (178,000–267,000 cm –1 M –1 ) and good fluorescence quantum yields, resulting in high overall brightnesses. Remarkably, the selenium-containing dyes featuring terminal indole and benzoindole-type units exhibited impressive singlet oxygen quantum yields of around 13%, a standout performance in the deep-NIR region. These values are particularly promising and highlights the potential of these dyes for deep-NIR imaging and photodynamic applications.