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

Experimental support is provided for the charge localization in squaraines, a class of fundamentally and technologically important organic dyes, by H-1 NMR analysis through a host-guest complexation approach. Specific binding of Ca2+ 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.