1H NMR spectral evidence for a specific host-guest complexation induced charge localization in squaraine dyes

[reaction: see text]. Experimental support is provided for the charge localization in squaraines, a class of fundamentally and technologically important organic dyes, by (1)H NMR analysis through a host-guest complexation approach. Specific binding of Ca(2+) ions to the squaraine 2 with a podand sidearm resulted in a charge-localized structure 2a with dramatic shifts and resolution of the proton signals when compared to those of 2.     

Redox-switchable squaraines with extended conjugation

[reaction: see text] The redox chemistry of pi-extended squaraines is investigated using cyclic voltammetry, in-situ spectroelectrochemistry and quantum chemical calculations. Squaraine 1 is reversibly oxidized to the radical cation and dication whereas reduction shows limited electrochemical but fully chemical reversibility. The radical cation of 1 reveals absorption bands at 1000 nm and a "two-band feature" at 1600 nm. Their implications on the intramolecular electron transfer are discussed.     

A novel approach toward low optical band gap polysquaraines

[reaction: see text] Polycondensation of 2,5-dialkoxydivinylbenzene-bridged bispyrroles and squaric acid resulted in extensively conjugated polymers with strong near-infrared (NIR) absorption around 800-1000 nm, which is a signature of their low band gap (E(g)). Conjugated polymers with such a strong NIR absorption are rare. One of the synthesized polysquaraines showed a significantly low E(g) of 0.79 eV with an intrinsic conductivity of 5.3 x 10(-4) S/cm.     

Conformational control in a bipyridine linked π-conjugated oligomer: cation mediated helix unfolding and refolding

A chiral π-conjugated oligomer having alternate bipyridine and carbazole moieties connected through acetylinic bonds undergoes helical folding in chloroform-acetonitrile (40/60, v/v) as evident by fluorescence and circular dichroism changes. In the presence of transition metal cations such as Zn(2+) defolding of the helical conformation occurs. Upon decomplexation of the cation with EDTA, the helical conformation is regained.