π-extended porphyrin dimers as efficient near-infrared emitters and two-photon absorbers

A Zn-porphyrin dimer and its linear conjugate with two diketopyrrolopyrrole (DPP) units have been prepared and their one- and two-photon photophysical properties have been characterised. The already wide conjugation of the dimer is further extended in the DPP containing derivative, leading to absorption and emission features in the near-infrared. The fluorescence quantum yield of the two compounds is of the order of 0.20 in organic solvents, a remarkable value for NIR emitting Zn-porphyrin systems. High two-photon absorption cross sections of 10,000 GM and 21,500 GM are measured at 910 nm for the dimer and the DPP conjugate, respectively, making these dimers promising for two-photon excited fluorescence imaging applications.