SYNTHESIS AND OPTICAL PROPERTIES OF 2,2′-BIIMIDAZOLE AND BENZO[d]IMIDAZOLE DERIVATIVES: CHANGING π-CONJUGATION BY PHOTOEXCITATION

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.