In order to achieve chromophores which absorb light in the far red or even in the near-infrared region (NIR), increased efforts were made by developing new molecular dye structures and synthetic strategies or by investigating basic structure property relationships. Intense absorption, e.g. in the NIR, is mandatory for many technologies and applications, like solar cells or sensors. However, while many dyes provide absorption from the visible to the NIR range, only few absorb in the NIR only and are able to convert energy efficiently. A few dye classes with appropriate molecular design are known to be viable NIR absorbers: squaraine dyes, croconine dyes, or polymethine dyes.
Polymethine dyes exhibit outstanding photophysical properties, for example, heptamethine dyes absorb light above 700 nm with a high molar extinction coefficient of over 100000 Lmol -1cm -1. Furthermore, squaraine and polymethine dyes can be obtain via straightforward and cost-effective synthesis in high yields.
Therefore, the development and synthesis of novel squaraine and polymethine dyes for photophysical applications is in the focus of our research.