Hitherto unknown unsymmetrical squaraines containing 2,3-dihydro-1H-perimidine terminal groups that are linked through the 4-position and the 6-positions of the 2,3-dihydro-1H-perimidine terminal groups to the four membered squaraine ring, were obtained as minor products in the reaction of squaric acid with 2,3-dihydro-1H-perimidines.The structure of these new squaraines was characterized by means of one-dimensional and two-dimensional NMR spectroscopy.The new unsymmetrical squaraines absorb in the NIR region between 777 nm and 781 nm in trichloromethane and between 801 nm and 804 nm in DMSO. This absorption behavior was compared to known symmetrical squaraines of this series, and to previously reported 2,3-dihydro-1H-perimidine azo dyes. Thus, when compared to symmetrical squaraines in which both 2,3-dihydro-1H-perimidine terminal groups are linked through their 4-position to the squaraine moiety, the unsymmetrical dyes absorb hypsochromically. Conversely, if the unsymmetrical dyes are compared with symmetrical squaraines that are linked through the 6-position of the 2,3-dihydro-1H-perimidine ring system, then they absorb at longer wavelengths.Syn-anti isomerization of the unsymmetrical squaraines was investigated by means of 2nd order derivative UV-Vis spectroscopy and NMR spectroscopy, and the results compared with those obtained from the known symmetrical squaraine isomers. These studies indicated that squaraines, in which the 2,3-dihydro-1H-perimidine terminal groups are linked at their 4-positions, exist to a much greater degree in the anti form due to the presence of hydrogen bonding, whereas a far greater degree of syn-anti isomerism occurs in the other two isomers.