The proton and 13C NMR of azulene and dialkylaminohydroxyphenyl squaraines have been investigated. The four-membered ring carbon resonances occur in the 180-190 ppm range and are attributed to the cyclobutenediylium character of this structure. Some charge delocalization from the central ring to the pendent aromatic substituents was also observed, indicative of a substituent effect of the squaraine moiety on aminoaromatic systems ...
