Bright, color-tunable fluorescent dyes based on π-expanded diketopyrrolopyrroles

A synthetic approach to the structurally diverse family of π-expanded diketopyrrolopyrroles is described. A three-step strategy appears to be very general and starts with the preparation of diketopyrrolopyrroles followed by N-alkylation with bromoacetaldehyde diethyl acetal and electrophilic aromatic substitution. The final reaction regioselectively furnishes S-shaped, violet and blue functional dyes of previously unknown structure. New dyes possess sharp absorption and emission peaks, with very high molar absorption coefficients and reasonable fluorescence quantum yields. As a proof of principle, cell uptake of selected dye was demonstrated.