Diketopyrrolopyrrole-porphyrin arrays as NIR emitters and NIR-activated photosensitizers

Porphyrins are attractive photoactive molecules widely used in energy conversion structures, linear and non-linear materials for optoelectronics and biomedical research. Extending the porphyrin p-system by conjugation with proper units is an advantageous tool to control and finely tune the HOMO-LUMO gap of porphyrin-based arrays and to modulate their absorption and emission features. This approach is particularly interesting to develop systems with absorption and/or luminescence in the near-infrared (NIR) spectral region, promising for biomedical (imaging, sensing), optoelectronic and energy conversion applications [1]. The extended conjugation, moreover, favours non-linear optical properties such as two-photon (TP) absorption [2], useful for TP-activated photodynamic therapy with increased 3D spatial resolution and reduced tissue damaging. In this contest, in collaboration with the group of Prof. V. Heitz (University of Strasbourg), we recently investigated several diketopyrrolopyrrole-porphyrin conjugates, where the arrays are composed by monomeric or dimeric porphyrin systems conjugated to diketopyrrolopyrrole units. These systems have been proven to be promising photosensitizers for one- and two-photon photodynamic therapy and efficient NIR emitters [3-5], with potential as active materials in luminescent solar concentrators. Further combination of the conjugates with selected functional units allowed to achieve MRI contrast [6, 7] or tumour targeting [8], leading to promising systems for theranostics and tumour-targeted photodynamic therapy. Detailed investigation of the photophysical properties of the arrays allowed to characterize singlet and triplet excited states features and to understand structural-property relationships, important to optimize the design of efficient NIR-responsive materials.