Photochromic Hybrid Containing <i>In Situ</i>-Generated Benzyl Viologen and Novel Trinuclear [Bi₃Cl₁₄]^5–: Improved Photoresponsive Behavior by the π···π Interactions and Size Effect of Inorganic Oligomer

Abstract

Two new member of (V)_{(2<i>n</i>+2)/2}[Bi_2<i>n</i>Cl_8<i>n</i>+2] series hybrids, (BzV)₂[Bi₂Cl₁₀] (<b>1</b>) and (BzV)₅[Bi₃Cl₁₄]₂·(C₆H₅CH₂)₂O (<b>2</b>) (where BzV²⁺ = <i>N</i>,<i>N</i>′-dibenzyl-4,4′-bipyridinium and (C₆H₅CH₂)₂O = dibenzyl ether) have been obtained, and compound <b>2</b> contains an unprecedented discrete trimer [Bi₃Cl₁₄]^5– counterion. The novel <i>in situ</i>-synthesized symmetric viologen cation with aromatic groups on both sides of 4,4′-bipy would provide more opportunities to create π···π interactions to optimize the photochromic property of the hybrid, and different bismuthated-halide oligomers enable us to discuss the size effect in this series of compounds. Both <b>1</b> and <b>2</b> are photochromic, and their photoresponsive rate is faster than that of reported viologen–metal halide hybrids. Experimental and theoretical data illustrated that the size of the inorganic oligomer can significantly influence the photoresponsive rate of the viologen dication, and the π···π interaction behaves as not only a powerful factor to stabilize the viologen monocation radical but also the second electron-transfer pathway, from a π-conjugated substituent to a viologen cation, for the photochromic process