Facile synthesis and exploration of excited state assisted two-photon absorption properties of D-A-D type thiophene-pyridine derivatives.

A series of trigonal-shaped molecules (TPyT and TPyP) and a polymer (P2TPy) with donor-acceptor-donor (D-A-D) structural arrangement were designed with thiophene and 2,4,6-trisubstituted pyridine as the backbone i.e., a 4-(4-(decyloxy)phenyl)-2,6-di(thiophen-2-yl)pyridine core structure, for the first time and synthesized via a microwave assisted one pot reaction. The extension of conjugation of the system by substituting thiophene acrylonitrile (TPyT) and phenyl acrylonitriles (TPyP and P2TPy) via low cost condensation reactions improved the linear optical, electronic and thermal properties of the synthesized compounds. Furthermore, the nonlinear absorption (NLA) was also enriched appreciably by increasing the conjugation. The three compounds showed an "effective two-photon absorption" phenomenon with the NLA coefficient (βeff) of the order of 10-10 m W-1. The suitability to be utilized in the fabrication of all-optical limiting devices is best achieved by polymer P2TPy as it exhibits substantially higher βeff (7.02 × 10-10 m W-1) and an extremely low optical limiting threshold (1.42 J cm-2).