Solid-state emissive Zn2+ directed metallo-supramolecular polymers of bis-terpyridine appended aryl substituted buta-1,3-diene derivatives: Synthesis, photo-physical and electrochemical properties

Abstract

Herein, two solid-state emissive monomers (TBBTP and ABTP) of bisterpyridine (bis-tpy) appended with twisted aryl substituted buta-1,3-diene central core have been designed and developed to investigate metal directed assembly to metallo-supramolecular homopolymers, TBBTP-Zn and ABTP-Zn and a copolymer, ATBBTP-Zn with zinc ion. The formation as well as purities of the monomers have been checked by NMR, FT-IR spectroscopy and mass spectrometry studies and the polymers have been characterised via NMR and FT-IR studies. Prior to optical studies, density functional theory (DFT) studies have been performed to rationalize the electronic distributions in HOMOs and LUMOs of monomers and their corresponding Zn complexes to unveil the phenomenon of intramolecular charge transfer. Absorption and emission studies performed in solution as well as in solid state have indicated that the monomers and its metallo-supramolecular polymers are emissive in solution as well as in solid state. However, the emission maxima at 608 nm, 576 nm and 590 nm of the metallo-supramolecular polymers, TBBTP-Zn, ABTP-Zn and ATBBTP-Zn respectively are clearly red shifted from monomers (466 nm for TBBTP and 490 nm for ABTP) and the fluorescence lifetime values measured by time-correlated single photon counting (TCSPC) are increased in solution as well as in solid state after coordination with Zn2+ ion owing to the charge-transfer processes from the central butadiene part to zinc coordinated terpyridine moiety. The HOMO and LUMO energies, band gaps of monomers (2.95 eV for TBBTP and 2.85 eV for ABTP) and polymers (2.73 eV, 2.84 eV and 2.73 eV for TBBTP-Zn, ABTP-Zn and ATBBTP-Zn respectively) have been estimated via electrochemical methods and it reveals that both monomers as well as polymers may be used in optoelectronic application.