Quantitative\nExamination and Mechanistic Insights\nof Polymer Chain Conformation Confined in Nanopores by Time-Resolved\nFluorescence Resonance Energy Transfer

The conformational studies of polymers\nconfined at the nanoscale\nremain challenging and controversial due to the limitations of characterization\ntechniques. In this study, we utilized the high sensitivity of time-resolved\nfluorescence resonance energy transfer (<i>tr</i>FRET) and\na site-specific dye-labeling strategy to characterize the conformation\nof polymer chains confined in anodic aluminum oxide (AAO) nanopores.\nThis strategy introduced a fluorescent donor (carbazole) and acceptor\n(anthracene) at the center of poly(butyl methacrylate) (PBMA) chains\ngrown by atom transfer radical polymerization (ATRP). By quantitatively\nanalyzing fluorescence decay through the Förster mechanism\nand the Drake–Klafter–Levitz (DKL) formalism, we can\ndetermine both the energy transfer efficiency and the spatial distribution\nof the dyes. This analysis revealed that the PBMA chains, with a molecular\nweight of 40 kDa, maintained their bulk-like conformation even when\nconfined within nanopores as small as 10 nm in diameter. This study\nis the first to demonstrate the use of <i>tr</i>FRET for\ninvestigating chain conformation in confined polymer systems, which\ncan be generalized to other polymer types and polymer topologies in\ndifferent confined geometries.