Fluorescence Studies on a Thermoresponsive PNIPAM-Polyfluorene Graft Copolymer

Abstract

The fluorescence behavior of a PNIPAM-grafted polyfluorene copolymer (PF-PNIPAM) together with the corresponding precursor polymer (9,9bis(ω-carboxypentyl)-substituted polyfluorene, PF-COOEt) was investigated by UV− Vis spectroscopy and steady-state and time-resolved fluorescence techniques in DMF and in an acetone:water (1:2) mixture over the temperature range 5 to 70 °C. Temperature dependence plots show a clearly different behavior in the acetone:water (1:2) mixture, which, based on the overall data, is attributed to the occurrence of a lower critical solution temperature (LCST) for PF-PNIPAM, which is found at ∼45 °C, different from the value for PNIPAM chains in water of ∼32 °C. In the acetone:water (1:2) mixture, the weak temperature dependence of the fluorescence decay time components between 20 and 70 °C documents a dominant intra-and interchain hopping-type deactivation mechanism. However, additionally, the thermoresponsive PNIPAM side chains cause aggregate formation at the LCST temperature coupled to abrupt changes of the fluorescence intensity. Dynamic light scattering (DLS) studies for PF-PNIPAM also in the acetone:water (1:2) mixture in the temperature range of 20−55 °C show for T > 40 °C a unimodal size distribution peaking for diameters of >200 nm corresponding to aggregates, contrasting to a bimodal distribution with lower hydrodynamic radii at lower temperatures. The study delivers additional information to the puzzling LCST behavior of PNIPAM-based (co)polymers, which in PF-PNIPAM impacts the presence of both polyfluorene PF main chains and PNIPAM side chains.

Controlled Synthesis, Chiral Assembly, and Circularly Polarized Luminescence of Poly(Phenyl Isocyanide)‐Block‐Polyfluorene Copolymers

“…[18] Moreover, PFs can also be modified through copolymerization strategy, and various PF-containing copolymers have been investigated. [19][20][21] However, copolymers consisting of PF with chiral polymers are very limited, although they may exhibit exciting functionality, such as circularly polarized luminescence (CPL), that can be applied for constructing novel optoelectronic devices.…”

A Multiple-Responsive Fluorescence Probe Based on Water-Soluble Fluorescent Conjugated Polymer for Biomolecules Detection

“…Nowadays, owing to stable chemical structures, high quantum efficiency, and reliable performance, a fluorescent probe based on fluorescent conjugated polymers (FCPs) has become one of the focuses of researchers. However, due to the limitations of the extremely poor water solubility of FCP, most of the probe polymer molecules used to detect water-based samples need to undergo necessary water-soluble modification, − which often affects the substrate responsiveness dependent on special functional groups, thus reducing the detection ability. Therefore, reasonably adjusting the molecular structure to obtain water solubility while retaining high sensitivity as much as possible is the key to designing polymer fluorescent probes.…”

Fabrication and characterization of novel macroporous hydrogels based on the polymerizable surfactant AAc-Span80 and their enhanced drug-delivery capacity

“…8 Because of their excellent hydrophilicity, biocompatibility, and environmental sensitivity, PNIPAM hydrogels have attracted much scientic interest for domain applications in wound dressing, drug delivery, cell culture, tissue engineering, enzyme immobilization, etc. [9][10][11][12][13] However, the response of PNIPAM hydrogels is very slow, mainly due to the formation of an impermeable surface structure that slows the outward ow of water throughout the hydrogels wrinkling phenomenon. 14 On the one hand, the response speed can be improved by surface modication, such as graing using gold, 15 silica, 16 cellulose, 17 or polyacetal lactone (PCL).…”