Synthesis, properties and photo-responsive behavior of luminescent side chain polymers containing D–π-A α-cyanostilbene units†
A series of luminescent side chain polymers containing a D–π-A structure and different flexible spacer lengths, namely, poly[(Z)-ω-(4-(1-cyano-2-(4-cyanophenyl)vinyl)phenoxy)alkyl methacrylate]s (PMmPVPCN, m = 2, 4, 6, 8), were successfully prepared. With the combination of aggregation-induced emission enhancement (AIEE) luminogens and mesogens, the resultant polymers are expected to possess both liquid crystal characteristics and AIEE characteristics. The phase structure of PMmPVPCN was explored by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and one-dimensional wide-angle X-ray diffraction (1D WAXD). Photophysical properties of PMmPVPCN were studied by UV spectra and fluorescence spectra. Test results suggested that the phase structure of PMmPVPCN transformed from the amorphous phase (PMmPVPCN, m = 2, 4) to the nematic phase (PMmPVPCN, m = 6, 8) with the increase of polymer spacer length. All the synthetic monomers and polymers exhibited AIEE properties and the luminescence behavior of PMmPVPCN was associated with their chemical structure. The solid fluorescence quantum yields of PMmPVPCN increased from 22.4% to 42.7% with increasing spacer length. The polymer films also showed reversible fluorescence photo-responsive properties. The emission color and the emission intensity of polymer films changed when exposed to a 365 nm UV lamp. The change process was reversible and they could turn back to their original state when irradiated with a 254 nm UV lamp or heated at higher temperature.