Synthesis, characterization and ab initio investigation of a panchromatic ullazine-porphyrin photosensitizer for dye-sensitized solar cells

An ullazine unit was employed as a donor moiety in a donor-π-acceptor (D-π-A) motif, employing the porphyrin macrocycle as a π-system. Synthesis of this ullazine-porphyrin dyad containing sensitizer (SM63) was achieved and an investigation of the electrochemical and spectroscopic properties of this dye was performed. Introduction of the ullazine donor promoted significant enhancements in long and visible wavelength absorption, leading to panchromatic light harvesting. SM63 demonstrated a maximum absorption approaching 750 nm, a significant improvement compared to the model compound LD14-C8, which features a simpler donor component (4-(N,N-dimethylamino)phenyl) and an absorption onset at ∼700 nm. The dye SM63 was subjected to a rigorous ab initio investigation to gain further insight into its unique absorption and emission properties. Application of the molecular ullazine-porphyrin dyad SM63 into dye-sensitized solar cells afforded a device with significantly improved light harvesting abilities in both the visible region of the spectrum as well as NIR light (∼800 nm), demonstrating the value of ullazine unit in developing panchromatic dyes for light harvesting applications.