Belt-Shaped π-Systems: Relating Geometry to Electronic Structure in a Six-Porphyrin Nanoring
Artikel i vetenskaplig tidskrift, 2011

Linear pi-conjugated oligomers have been widely investigated, but the behavior of the corresponding cyclic oligomers is poorly understood, despite the recent synthesis of pi-conjugated macrocycles such as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an efficient template-directed synthesis of a pi-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 pi-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.

Författare

Johannes K. Sprafke

University of Oxford

Dmitry V. Kondratuk

University of Oxford

Michael Wykes

Université de Mons

Amber L. Thompson

University of Oxford

Markus Hoffmann

University of Oxford

Rokas Drevinskas

Lunds universitet

Wei-Hsin Chen

University of Oxford

Chaw Keong Yong

University of Oxford

Joakim Kärnbratt

Chalmers, Kemi- och bioteknik, Fysikalisk kemi

Joseph E. Bullock

Northwestern University

Marc Malfois

Diamond Light Source

Michael R. Wasielewski

Northwestern University

Bo Albinsson

Chalmers, Kemi- och bioteknik, Fysikalisk kemi

Laura M. Herz

University of Oxford

Donatas Zigmantas

Lunds universitet

David Beljonne

Université de Mons

Harry L. Anderson

University of Oxford

Journal of the American Chemical Society

0002-7863 (ISSN) 1520-5126 (eISSN)

Vol. 133 17262-17273

Drivkrafter

Hållbar utveckling

Styrkeområden

Nanovetenskap och nanoteknik

Fundament

Grundläggande vetenskaper

Ämneskategorier

Kemi

DOI

10.1021/ja2045919