Main-chain hyperbranched polyrotaxane: Synthesis, photophysical properties, and energy funnel

Abstract

A main-chain hyperbranched polyrotaxane (HBP) assembled by the interaction between dibenzo[24]crown-8 (DB24C8) and dibenzyl ammonium (DBA) was synthesized through Cu(I)-catalyzed azide-alkyne cycloaddition. Energy donors and acceptors were attached to DB24C8 and DBA units, respectively, to investigate the effect of such polyrotaxane structure on the intramolecular and intermolecular energy transfer channel. Our investigations indicated that HBP with higher molecular weight was obtained in relatively lower concentration. AFM, DLS, and SLS analyses revealed that our HBP molecule was described as a ball-shaped nanoparticle with the radius of about 4–8 nm. Benefitting from such unique topology, the aggregation of the chromophores through π-π stacking was effectively suppressed both in solution and in solid state. Meanwhile, the steady-state and time-resolved fluorescence characterization demonstrated that HBP exhibited the excellent energy funneling ability from A3 to B2 unit with high energy transfer efficiency and fast rate, which was attributed to the large spectral overlap between the emission features of the donors and the absorption of the acceptors, and the unique highly branched mechanically interlocked architecture. The energy transfer quantum yield of HBP was calculated to be as high as 99%, and this energy transfer process was estimated to occur with a rate of 7.58 × 109 s−1 with single exponential.