Redox-switchable squaraines with extended conjugation

graphics The redox chemistry of pi-extended squaraines is investigated using cyclic voltammetry, in-situ spectroelectrochemistry and quantum chemical calculations. Squaraine 1 is reversibly oxidized to the radical cation and dication whereas reduction shows limited electrochemical but fully chemical reversibility. The radical cation of 1 reveals absorption bands at 1000 nm and a two-band feature at 1600 nm. Their implications on the intramolecular electron transfer are discussed.