CoeusCy7 · Aril-fused Heptamethine Cyanine dyes, Synthesis, Photophysics, and Photochemistry

An unparalleled advantage of light as a control stimulus, such as tunability, high spatial and temporal precision, and orthogonality towards biochemical systems, is relatively well established. However, the application of light for phototherapy in living organisms is limited by the intrinsic properties of biological tissues, allowing for significant penetration depth only in the 650 – 900 nm range. This restriction calls for a careful design of the chromophore intended for phototherapy. Heptamethine cyanine dyes are well-suited to meet the wavelength requirements essential for modern bioimaging techniques and chemistry. The biocompatibility, photochemical, and photophysical parameters of these dyes can be adjusted by varying substituents at different positions along the heptamethine chain. The CoeusCy7 project aims to synthesize cyanine dyes with aryl groups fused in the various positions of the heptamethine chain and novel types of chain substitution. A notable feature of these novel dyes is the Z configuration of the C=C bond imposed by the aromatic ring. The objective is to investigate these cyanine dyes in terms of their photophysical and photochemical properties, focusing on absorption characteristics, chemical stability, and photostability. Novel cyanine dyes are expected to exhibit bathochromic shifts in their absorption and emission spectra and to modulate other photophysical properties, such as quantum yields of accompanied chemical processes, intersystem crossing efficiency, and affinity for or production of singlet oxygen. These novel cyanine dyes would be a valuable addition to the current repertoire, expanding the scope of their photophysical, (photo)chemical, and biological applications. Moreover, the CoeusCy7 project will contribute to an advanced mechanistic understanding of the Zincke reaction used for their synthesis and will provide deeper insights into their structure and photophysical/photochemical properties.