Enhanced photoelectrical properties of alizarin-based natural dye via structure modulation

A series of new dyes (AL01-AL02t) were designed through introducing different conjugated bridges into the position of two hydroxyl groups on the natural dye 1,2-dihydroxyanthraquinone (alizarin), and their photoelectrical properties were systematically investigated as the dyes applied in the field of dye-sensitized solar cell (DSSC) via the density functional theory (DFT) and time-dependent DFT methods. Moreover, the key parameters related to the intramolecular charge transfer (ICT) properties of the dyes, such as the transferred charge and charge transferred distance were calculated. In addition, the light harvesting efficiency, free-energy change driving force, electron regeneration driving force and chemical reactivity parameters were obtained to evaluate the photoelectrical properties of the investigated dyes. The calculated results indicate that the designed dyes would show the better photoelectrical properties, owing to their lower energy gaps, red-shifted absorption spectra, the greater transferred charge and charge transferred distance. Therein, it is worth noting that the designed dye AL02t displays the lowest energy gap, widest absorption spectrum, smallest hole and electron reorganization energies, lowest electron regeneration driving force and chemical hardness, largest electro-accepting power and electrophilicity values, which mean that this designed dye would present the best photoelectrical properties among the investigated dyes. Significantly, the better optical and electrical characteristics of AL02-series dyes than that of AL01-series dyes indicate the modification for the hydroxyl group on R2 position of alizarin is more beneficial to improving its photoelectrical properties, which can provide a valuable reference for synthesizing the dyes with higher efficiency based on natural dyes in experiments.