Sprafke, Johannes KJohannes KSprafkeKondratuk, Dmitry VDmitry VKondratukWykes, MichaelMichaelWykesThompson, Amber LAmber LThompsonHoffmann, MarkusMarkusHoffmannDrevinskas, RokasRokasDrevinskasChen, Wei-HsinWei-HsinChenCHAW-KEONG YONGKärnbratt, JoakimJoakimKärnbrattBullock, Joseph EJoseph EBullockMalfois, MarcMarcMalfoisWasielewski, Michael RMichael RWasielewskiAlbinsson, BoBoAlbinssonHerz, Laura MLaura MHerzZigmantas, DonatasDonatasZigmantasBeljonne, DavidDavidBeljonneAnderson, Harry LHarry LAnderson2022-12-162022-12-162011-11-020002-7863https://scholars.lib.ntu.edu.tw/handle/123456789/626531Linear π-conjugated oligomers have been widely investigated, but the behavior of the corresponding cyclic oligomers is poorly understood, despite the recent synthesis of π-conjugated macrocycles such as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an efficient template-directed synthesis of a π-conjugated butadiyne-linked cyclic porphyrin hexamer directly from the monomer. Small-angle X-ray scattering data show that this nanoring is shape-persistent in solution, even without its template, whereas the linear porphyrin hexamer is relatively flexible. The crystal structure of the nanoring-template complex shows that most of the strain is localized in the acetylenes; the porphyrin units are slightly curved, but the zinc coordination sphere is undistorted. The electrochemistry, absorption, and fluorescence spectra indicate that the HOMO-LUMO gap of the nanoring is less than that of the linear hexamer and less than that of the corresponding polymer. The nanoring exhibits six one-electron reductions and six one-electron oxidations, most of which are well resolved. Ultrafast fluorescence anisotropy measurements show that absorption of light generates an excited state that is delocalized over the whole π-system within a time of less than 0.5 ps. The fluorescence spectrum is amazingly structured and red-shifted. A similar, but less dramatic, red-shift has been reported in the fluorescence spectra of cycloparaphenylenes and was attributed to a high exciton binding energy; however the exciton binding energy of the porphyrin nanoring is similar to those of linear oligomers. Quantum-chemical excited state calculations show that the fluorescence spectrum of the nanoring can be fully explained in terms of vibronic Herzberg-Teller (HT) intensity borrowing.enCONJUGATED PORPHYRIN OLIGOMERS; DENSITY-FUNCTIONAL THEORY; ABSORPTION CROSS-SECTION; X-RAY SOLUTION; CRYSTAL-STRUCTURES; BUILDING-BLOCKS; EXCITED-STATE; BIOLOGICAL MACROMOLECULES; PERSISTENT MACROCYCLE; NANOMETER REGIMEjournal article10.1021/ja2045919219392462-s2.0-80055019999WOS:000297380900031https://api.elsevier.com/content/abstract/scopus_id/80055019999