Geometrically precisely defined multinanometer expansion/contraction motions in a resorcin[4]arene cavitand based molecular switch
Geometrically precisely defined multinanometer expansion/contraction motions in a resorcin[4]arene cavitand based molecular switch
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DOI：
10.1002/anie.200500970
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Diederich, F
中科院分区：
文献类型：
--
作者：
Azov, VA;Schlegel, A;Diederich, F
The invention of molecular devices that undergo reversible controlled mechanical movements on the nanometer scale and thereby mimic natural phenomena such as muscle expansion/contraction is a hot target in contemporary chemistry.[1] Elegant examples of molecular and supramolecular switches with bistable conformations of profoundly different geometry have been described in recent years.[2–7] On the other hand, the conformational space available in the contracted and expanded states of the reported systems often is rather large and the geometric differences not always well defined. We became interested in developing a rigid molecular system in which both states adopt a precisely defined geometry and report here a first example based on a bridged resorcin [4] arene scaffold. These cavitands, first introduced by Cram and co-workers,[8] can be reversibly switched between a contracted (vase) and an expanded (kite) conformation upon variation of temperature [8–10] or pH,[11] or upon metal-ion addition.[12] Recent advances in the synthesis of partially or differently bridged resorcin [4] arene cavitands [13, 14] enabled the preparation of 1, in which two opposite cavity walls are greatly extended by attachment of rigid oligo (phenylene ethynylene) arms. A donor–acceptor BODIPY (dipyrrometheneboron difluoride) dye pair [15] is attached to the oligomeric termini to allow observation of the switching process by fluorescence resonance energy transfer (FRET).[16] BODIPY dyes were chosen for the targeted pH-induced switching, since their emission behavior features low sensitivity to pH and environmental polarity, as we could confirm in model studies. Computer model building,[17] based on X-ray crystal structures of bridged resorcin [4] arene cavitands in both vase and kite conformations,[12, 13b] suggested a% 1000% difference in the distance between the dye pair in the contracted (% 7) and expanded (% 7 nm) states (Figure 1), which should allow convenient detection of different FRET behavior in the two states.[16a]The synthesis of 1 proceeded in a highly convergent manner. Sonogashira cross-coupling [18] of 2 [15b] with Me3Si-C CH afforded 3, which was deprotected to give 4. A second cross-coupling with aryl iodide 5 [19] provided 6, which was deprotected to yield the donor dye-appended 7. A similar route led from 8 [15a](via 9! 10! 11) to the acceptor building block 12 (Scheme 1).
