Control of the arrangement of dipolar orientation of pyrimidine inside the conjugated backbone.

[figure: see text] Linear molecules with different arrangement of dipolar pyrimidine moieties in the pi-conjugated backbone were synthesized by a Pd-catalyzed Sonogashira coupling reaction. Significant reduction of the HOMO-LUMO energy band gap and improvement of fluorescence quantum yield were observed upon incorporating pyrimidine into the conjugated backbone.