Avenues into the synthesis of illusive poly(m-phenylene-alt-squaraine)s: polycondensation of m-phenylenediamines with squaric acid intercepted by intermediate semisquaraines of exceptionally low reactivity

The synthesis and properties of a novel class of ortho-dialkylamino-substituted semisquaraines are described. The exceptionally low reactivity of the investigated compounds is caused by an intramolecular hydrogen bond as evidenced by experimental and computational studies. Although this constitutes the reason for our failed attempts to prepare poly(m-phenylene-alt-squaraine)s, the discovered influence of hydrogen bonding on the photophysical properties of these semisquaraines provides a promising new motif for sensor design.