Coumarin‐Based ATRP Initiator: Structural Decoupling and Structure–Photophysics Correlation Revealed by Experiment and Theory

ABSTRACT

The integration of fluorescent chromophores with atom transfer radical polymerization (ATRP) initiators enables the preparation of functional fluorescent polymers, although the influence of the initiating group on fluorophore electronic structure and photophysical properties remains unclear. In this study, a trifluoromethyl‐substituted coumarin‐based ATRP initiator was synthesized and investigated using experimental and computational methods. Structural characterization was performed by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. Controlled ATRP of styrene produced well‐defined polystyrene ( M _n  = 22.0–30.0 kDa, Đ  = 1.19–1.26), while subsequent chain extension with N , N ‐dimethylaminoethyl methacrylate yielded block copolymers ( M _n up to 42.2 kDa, Đ  = 1.38–1.43), confirming excellent chain‐end fidelity. The coumarin fluorophore retained its fluorescence after polymerization. Density functional theory (DFT), the Tamm–Dancoff approximation (TDA), and natural transition orbital (NTO) analyses showed that the frontier molecular orbitals and lowest‐energy excited states remain localized on the coumarin π‐system, with minimal contribution from the bromoisobutyrate initiating group. These findings demonstrate structural and electronic decoupling between the chromophore and initiator, explaining the preservation of fluorescence and providing insight into structure–electronic structure–photophysical relationships in multifunctional ATRP initiators.