关键词: 水溶性共轭聚合物, 光学性质, 聚集行为, 冷冻干燥

Water-soluble conjugated polymers have attracted enormous attention because of their water solubility and attractive optical properties. However, they often suffer from low emission quantum yield due to their strong inter-chain interaction and concomitant exciton quenching, especially in the solid state. To enhance the emission of the water-soluble conjugated polymers, strategies of decreasing the aggregation tendency of the polymers and controlling the backbone conformations are often adopted. In this work, to solve the problem of aggregation-caused quenching of luminescent conjugated polymer dilute solution during drying, we regulate the aggregation behavior and backbone conformation of a water-soluble conjugated polythiophene (PMNT) with polyvinyl alcohol (PVA) by intermolecular interactions, e.g. hydrogen bonding, and obtained tunable emissive PMNT thin films. Specifically, when PMNT in solution state is blended with PVA, obvious red shift of absorption and emission maxima and higher fluorescence intensity are observed, indicating that PVA molecules isolate the PMNT chains, reduce the degree of chain flexibility and increase backbone rigidity. Furthermore, by varying dry methods, we obtained PMNT solid films of tunable light absorption/emission properties: the solid films fabricated through splat cooling and in-situ lyophilization preserve the optical properties of the mixed solution of PVA and PMNT; the films fabricated through heat drying exhibit the similar optical properties with those of PMNT solution without adding PVA. Moreover, the emission quantum yield of the solid film prepared by the lyophilization method was enhanced compared with that of the solid film prepared by heat drying. These results suggest that the aggregation/conformation regulations of PMNT solution by PVA are retained in different degrees dependent on the drying methods: heat drying only maintains the isolation effect of PVA on PMNT; lyophilization readily preserve the interactions between PVA and PMNT, locking their disperse states and conformations. This study provides a strategy for regulating the aggregation behaviors and optical properties of solid conjugated polymers from the perspective of drying method.

Key words: water-soluble conjugated polymer, optical property, aggregation behavior, freeze drying