New Synthetic Approach to Squarylium Near Infrared Dyes

The 1,3-bis(4-aminoaryl)squaraines showed colour change behaviour, they were found to undergo reduction with sodium borohydride in solution to give colourless leuco compounds, which oxidised readily in air back to the coloured squaraine dye. We have shown that oxidation of the parent leuco-squaraines gives the neutral squaraine system. Initial observations indicated that the derivatives gave new long-wavelength absorbing chromophores, and It is interesting to note that the onidation of the leuco squaraines did initially produce a species absorbing at longer wavelengths than the parent squaraine dye. This colour-change redox behaviour has potential in the area of peroxidase-based bioassays and artificial camouflage.