π-conjugated polymers containing pendant Mn12 cluster: Synthesis and physical properties

In this paper two conjugated polymers containing polyfluorene chain with pendant carboxyl group (P1 and P2) are synthesized via Suzuki reaction, and then two corresponding polymers containing the pendant Mn-12 cluster core (Mn-12-P1 and Mn-12-P2) are obtained through exchange of the pendant carboxyl group in the polymers with acetate ligand of Mn-12-Ac. All the polymers show similar UV-vis absorption spectra with maximum peak at 388 nm and fluorescence emission spectra with maximum peak at 419 nm and a shoulder at 443 nm that can be attributed to the polyfluorene chain. The cyclic voltammetry measurement indicates that Mn-12-P1 or Mn-12-P2 exhibit similar electrochemical behavior to that of the corresponding P1 or P2. These indicate that the introduction of Mn-12 cluster at the side-chain of the conjugated polymers has little influence on the photophysical and electrochemical properties of the conjugated main-chain. However, compared with pristine Mn-12-Ac the magnetic properties of the modified Mn-12 cluster has been changed after substitution of acetate group by the pendant carboxyl group of the polymer. Both of the Mn-12 clusters modified by the conjugated polymer (Mn-12-P1 and Mn-12-P2) show paramagnetism in the range of 2-300K, and no SMM magnetic behavior is observed at low temperature. (C) 2011 Elsevier Ltd. All rights reserved.