Effects of temperature and CO2 pressure on the emission of N,N′-dialkylated perylene diimides in poly(alkyl methacrylate) films. Are guest-host alkyl group interactions important?

Abstract

Static and dynamic fluorescence measurements have been made on four N, N −dialkylated perylene diimides in films of poly(alkyl methacrylate)s (PAMAs) with 5 different alkyl groups and in a 'model solvent', n-butyl acetate, over wide temperature ranges. The results indicate that the excited singlet states of the perylene guest molecules are controlled primarily by chain relaxations rather than hole free volumes in the polymer matrixes. The short singlet lifetimes of the perylene molecules require that the guest molecules respond primarily to the environments experienced by their ground states within the PAMA matrixes; each of the PAMAs offers slightly different locations in which the guest molecules can reside as a result of interactions between the N −alkyl substituents on the imide groups of the perylenes and the alkyl groups on the PAMA side chains. PAMAs with branched side chains were found to have a larger influence than PAMAs with linear side chains on the fluorescence properties of the guest molecules. The results are compared to those employing pyrenyl derivatives (with much longer excited singlet lifetimes) in the same PAMA films. The overall results indicate that the perylenes can be used as a complementary probe of local polymer chain dynamics, but they are less sensitive to their environments than are pyrenyl groups. However, they offer some distinct advantages: (1) a much wider range of N, N −disubstituted perylene diimides can be synthesized easily; (2) those substituents can be designed to allow a greater or lesser interaction with an anisotropic host matrix. Also, rapid conformational changes of a bis-perylene derivative appear to be restricted in the polymer matrixes. Those restrictions appear reduced when the polymer films are placed under high pressures of the plasticizing gas, CO 2 , but not when they are under equal pressures of a much less intervening gas, N 2 .

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Electrospun Polymer Fibers Containing a Liquid Crystal Core: Insights into Semiflexible Confinement

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