Functional Ortho-Phenyleneethynylenes

1. Functional Ortho-Phenyleneethynylenes Georgia Tech Research Corporation - GA Institute of Technology Uwe Bunz, DMR 0454471 Cross-conjugated chromophores A-I have been made by Wittig-Hor­ner and Sonoga­shira type couplings. Cruci­forms with distinct donor-acceptor character show HOMOs that are fully localized on the distyryl­ben­zene branch of the mo­le­cule, while their LUMOs are localized on the bis(phenylethynylbenzene) branch.] The crucifroms B and D form well-defi­ned nano­structures when their THF solu­tions are precipi­tated into water. While B gives nanospheres, D grows almost mono­dis­perse, highly emissive nanocrys­tals. The nano­cry­stals are structurally identical to macro­scopic single crystalline specimens according to electron diffraction. Cruciforms are made using a unified synthetic route (Scheme 1). Cruciforms are attractive as metal cation sensors Fig. 4. The emission of G is blue-shifted from 570 nm to 421 nm upon addition of approx. 1 equivalent of zinc ions. However, if an excess of zinc ions (4.0 equivalents) is added, the emission red-shifts back, however only to 530 nm. These cruciforms show a dual emissive response Upon exposure to zinc triflate B shows a blue-shift, F shows a red shift and G shows first a blue shift and then a slight red shift in absorption when exposed to an excess of zinc ions; the blue shift in the case of B is quite impressive, but the red shift in the case of F is only visible in the shoulders of the respective absorptions.

2. Functional Ortho-Phenyleneethynylenes Georgia Tech Research Corporation - GA Institute of Technology Uwe Bunz, DMR 0454471 B F G G+H+ Fig. 1. Emission spectra of B,F and G upon exposure to zinc triflate in dichloromethane and to H+. The spectral pro­per­ties of G can be viewed as a super­position of the spectral properties of B and F, even though the transitions that are polarized along the bis-AE axis are more al­lowed in G than they are in F. The reason is not clear but warrants further investigation. A noteworthy point is the preference of Zn2+ for the aniline nitrogen bases in G over the pyridine ones, which came as a surprise.64We investigated the chromic responses of B,F,G to other metals. Fig. 5 shows the results obtained with several metal cations in dichloromethane. While K+ and Na+ do not bind, all other metal cations either lead to a shift in emission or quenching, but not in a fully predictable way. While Zn2+ and Mg2+ can not (yet) be discerned with these three most primitive cruciforms, Hg2+, Er3+ and Zn2+ can be discerned but only when the response of all three phores is analyzed. Differential responses were described by Anslyn to be powerful for sensory applications and should lead to more interesting results in the future. Fig. 2. A JACS communication has been published on these results Switching of intramolecular charge transfer in cruciforms: Metal ion sensing Wilson JN, Bunz UHF