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Paper | Special issue | Vol 88, No. 1, 2014, pp.261-273
Published online, 31st May, 2013
DOI: 10.3987/COM-13-S(S)12
Synthesis and Optical Properties of 2,2'-Biimidazole and Benzo[d]imidazole Derivatives: Changing π-Conjugation by Photoexcitation

Shoji Matsumoto,* Yu Zhao, and Motohiro Akazome

*Department of Applied Chemistry and Biotechnology, Graduate School and Faculty of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Abstract

1,1′,5,5′-Tetraaryl-2,2′-biimidazole and benzo[d]imidazole derivatives were synthesized. Symmetrical and unsymmetrical benzo[d]imidazole derivatives could be obtained by the Pd-catalyzed coupling reaction between 2-iodo-benzo[d]imidazole and the corresponding (benzo)imidazole anion. Hypsochromic shifts in absorption and fluorescence spectra of 1,1′,5,5′-tetraaryl-2,2′-biazole were observed by switching pyrrole rings for imidazole and benzo[d]imidazole rings, resulting in compounds with various Stokes shifts. Based on the (TD)DFT calculation, it was reasoned that changing the conformation of each single bond from a twisted to planar structure by photoexcitation led to larger Stokes shifts.