Dyes with tunable absorption properties from the visible to the near infrared range: 2,4,5,7-tetranitrofluorene (TNF) as a unique electron acceptor

Abstract Fourteen dyes based on 2,4,5,7-tetranitrofluorene (TNF) as the electron acceptor have been designed and prepared in a one-step synthesis. By modifying the electron donor, optical properties of the dyes could be efficiently tuned and an absorption ranging between 450 nm and 700 nm could be determined by UV-visible absorption spectroscopy. To get a deeper insight into the optical properties, solvatochromism of the fourteen dyes has also been examined. For all dyes, a positive solvatochromism was determined using different solvent polarity scales such as the Kamlet-Taft and the Catalan empirical scales. Finally, electrochemical properties were also examined, and a comparison of the electrochemical and optical bandgaps could be established. Theoretical calculations were also performed to characterize the different dyes.