Molecular-Weight-Dependent Fluorescence in Non-conjugated Polynorbornene: Decoupling Single-Chain Entanglements and Aggregation Effects

Abstract Fluorescent polymers enable precise modulation of photophysical properties through controlled chain architecture; however, systematic decoupling of intrachain and interchain fluorescence contributions remains a significant challenge. Here, non-conjugated polynorbornene (pNB) is employed as a model backbone to investigate how chromophore planarity and degree of polymerization (DP) govern fluorescence mechanisms. Three homopolymers—pNBAn (planar anthracene), pNBDPQ (non-planar diphenyl quinoline), and pNBTPE (AIE-active tetraphenylethylene)—were synthesized via living ROMP (Ð ≤ 1.30, DP = 10–300). DLS confirmed single-chain morphology under all dilute-solution conditions, ruling out large-interchain aggregation. pNBAn exhibits progressive fluorescence quenching with increasing DP via intrachain entanglement; pNBDPQ undergoes a DP-dependent 76 nm emission red-shift with an isosbestic point in chloroform, attributed to chromophore planarization within entangled single chains; and pNBTPE displays DP-amplified AIE upon water addition, with π-stacking confirmed by HR-TEM. These findings establish both polymer DP and chromophore planarity as the key structural parameters governing intrachain fluorescence mechanisms in non-conjugated pNB systems.