We report the synthesis and properties of a novel through-space conjugated polymer with a [2.2]paracyclophane skeleton. The obtained polymer possessed donor (fluorene) and acceptor (2,1,3-benzothiadiazole) segments that were alternately -stacked in proximity via the [2.2]paracyclophane moieties. The good overlap between the emission peak of the donor unit (fluorene) and the CT band of the acceptor unit (2,1,3-benzothiadiazole) caused fluorescence resonance energy transfer, and the visible green light emission from the acceptor unit was observed. 1. Introduction Since [2.2]paracyclophane was first prepared by Brown and Farthing in 1949 [1], [ ]paracyclophane consisting of two benzene rings closely linked (distance of approximately 2.8–3.1？？) by two ethylene bridges at para positions, it has been attracting attention [2–4]. However, even though cyclophane compounds have been receiving considerable attention in the field of organic chemistry, only several reports [5–23] on the synthesis of [ ]paracyclophane-containing polymers have been published in the field of polymer chemistry. In particular, only a few reports on conjugated polymers containing [ ]paracyclophane in the polymer main chain have been published [5–7, 20–23]. Recently, we successfully synthesized novel through-space conjugated polymers possessing [ ]paracyclophanes as a repeating unit into the main chain [5–7, 24–38]. We elucidated their properties and found that the conjugation lengths of these polymers extend via the stacked -electron systems. In addition, we synthesized [2.2]paracyclophane-layered polymers by treating pseudo-p-diethynyl[ ]paracyclophane with diiodoxanthene as a scaffold [39–42]. A one-dimensional -stacked structure can be readily obtained by incorporating a [ ]paracyclophane unit into a conjugated polymer backbone. As shown in Scheme 1, for example, copolymerization of pseudo-p-diethynyl[ ]paracyclophane with 2,5-dialkoxy-1,4-diiodobenzene yields a through-space conjugated polymer comprising a stacked -electron system, that is, a stacked xylyl-phenylene-xylyl unit. Therefore, the properties of through-space conjugated polymers synthesized by using a [2.2]paracyclophane monomer depend on this stacked -electron system (Scheme 1). We elucidated that the polymer emitted efficiently ( = 82% in diluted CHCl3 solution) [35] not from the excimer of the stacked xylyl-phenylene-xylyl segments but from the xylyl-phenylene-xylyl segment itself, irrespective of the -stacked structure of the polymer chain [6, 7, 43–45]. Scheme 1: -Stacked structure of a through-space conjugated polymer
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