Photophysical properties of p-extended diketopyrrolopyrrole-porphyrin arrays

Porphyrins are attractive photoactive units widely used in energy conversion structures, in linear and non-linear materials for optoelectronics and in biomedical research. Extending the porphyrin p-system is an interesting tool to control electronic coupling, to fine tune the HOMO-LUMO gap and to modulate absorption and emission features. This approach is promising to develop biomimetic light-harvesting antennas and reaction centres, photosensitizers for dye-sensitized solar cells and molecular wires. In addition, the near-infrared absorption and emission features of p-extended porphyrins render them particularly appealing for biomedical (imaging, sensing), optoelectronic and energy conversion applications [1]. We recently investigated new hydrophilic diketopyrrolopyrrole-porphyrin conjugates, as photosensitizers for one- and two-photon photodynamic therapy and as efficient near-infrared emitters. The arrays are composed by monomeric or dimeric porphyrin systems conjugated to one to four diketopyrrolopyrrole units (Figure 1). The photophysical properties in terms of absorption, luminescence, triplet excited state transient absorption and singlet oxygen generation will be presented and discussed in relation to the structure and the extent of conjugation of the array. Interestingly, the more conjugated systems show higher fluorescence quantum yields in the near-infrared, while a decrease in the singlet oxygen quantum yield is observed and ascribed to the decrease of the triplet energy level [2-4].