Effect of heteroatom (S/Se) juggling in donor-acceptor-donor (D-A-D) fused systems: synthesis and electrochemical polymerization

A series of nitrogen-bridged donor-acceptor-donor (D-A-D) type molecules, 1-3, was synthesized using thiophene/selenophene as donors and benzothiadiazole(BTD)/benzoselenadiazole(BSeD) as acceptors. Compound 1 contains a sulfur (S) atom in both the donor and acceptor which was changed to selenium (Se) in 2 for the donor and in 3 for the acceptor. The juggling of S/Se atom(s) in the donor or acceptor unit helps in modulating the structural, photophysical, and electrochemical properties of the resulting compounds. As revealed from crystal structures, compounds 2 and 3 dimerize via S center dot center dot center dot N and Se center dot center dot center dot N interactions, respectively. Compounds 1-3 were successfully polymerized by electrochemical polymerization and the resulting polymers were studied electrochemically. Compounds 1-3 show high fluorescence quantum yields, positive solvatochromism, and high stokes shifts.