New push-pull dyes based on 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b] naphthalen-1-ylidene)malononitrile: An amine-directed synthesis

A series of twelve dyes have been designed using 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene) malononitrile as the electron acceptor. While using piperidine as a classical base for the Knoevenagel reaction, a nucleophilic attack of the amine on the formed push-pull chromophore occurred, producing an azafluorenone derivative. By varying the amine, a series of azafluorenones could be obtained. By using an aldehyde of extended conjugation, a spontaneous aromatization following the cyclization reaction could also be demonstrated. The optical and electrochemical properties of the different dyes were examined. Theoretical calculations were also carried out to support the experimental results.