Creating more effective functional materials: altering the electronics of conducting metallopolymers for different applications.

Abstract

Conducting metallopolymers possess attractive electronic properties for use in sensors, photoelectronic devices, catalysts, and other applications. Modification of the conducting polymer backbone, through chemical or electrochemical methods, enables control of catalytic, electronic, and optical properties of the metal via inductive modulation of the electron density. Understanding in detail the relationship between the metal and polymer backbone could lead to more effective metallopolymer materials. We hope to study this relationship by probing the band gaps, excited state energy levels, catalytic activity, and sensor function in four metallopolymer systems.

Devices with sub-stochiometric ratios of Cu2ZnSnS4 NPs (CZTS: (Cu2Sn)1-xZn1/xS)(0≥x≥0.75)) grown in Cu(II) conducting metallopolymers were produced to study band gap tuning in hybrid materials. The valence and conductance bands of CZTS (x = 0.60) aligned with the HOMO/LUMO of the Cu(II) metallopolymer. Changing the alignment facilitated charge transfer in the hybrid material, leading to photovoltaic materials with efficiencies of ~0.1%.

Chemoresistive ionophore sensors were developed by incorporating selective binding groups, such as thiourea, into conducting polymer backbones. Thiourea monomers and polymers showed high selectivity for Pb(II) ions over many competitive ions. XPS experiments demonstrated that reversible chelation of Pb(II) ions could be achieved through a simple uptake/rinse process. The conductivity of the thiourea polymer increased fifty-fold, from 7.75×10−2 S/cm2 to 3.5 S/cm2, after Pb(II) exposure. Sensitivity measurements indicated the sensors have limits of detection near 10−10 M.

Highly conjugated ligands were synthesized to explore effective sensitization of visible and near-IR emitting lanthanides. (3,4-ethylenedioxy)thiophene was appended to dipyridophenazine and dipyridoquinoxaline to introduce a group that could be easily electropolymerized. These bi-functional ligands emitted from π-π* and an inter-ligand charge transfer excited states, and therefore, two distinct triplet states were observed. These separate energy pathways allowed for efficient sensitization of both visible (Tb(III), Eu(III), Dy(III)) and near-IR emitting (Nd(III), Yb(III), Er(III)) ions.

Finally, we explored the oxidation of a rhodium-containing conducting metallopolymer and the subsequent effect on the activity of the metal center. Oxidation of the backbone led to ancillary ligand attenuation, allowing for control of the catalytically active species in the conducting metallopolymer. Rh(I,III) monomer and metallopolymer catalytic studies showed potential for new heterogenous/homogeneous hybrid catalysts.