Theoretical Study on the Intermolecular Interactions of Black Dye Dimers and Black Dye–Deoxycholic Acid Complexes in Dye-Sensitized Solar Cells

Abstract

Herein the intermolecular interactions in Ru­(H₃tcterpy)­(NCS)₃ (black dye) dimers, where tcterpy is 4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine, deoxycholic acid (3α,12α-dihydroxy-5β-cholan-24-oic acid, DCA) dimers, and black dye–DCA complexes in acetonitrile were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT). Among the five resulting black dye dimers, the most preferable species (<b>BB1</b>) forms intermolecular hydrogen bonds via the carboxyl groups and has a centrosymmetric structure similar to that reported for a black dye crystal. Theoretical calculations indicate six black dye–DCA complexes, and the most stable configuration (<b>BC1</b>) has three intermolecular hydrogen bonds between the two carboxyl groups of the dye ligand and one carboxyl and two hydroxyl groups of DCA. <b>BC1</b> has a higher intermolecular interaction energy than <b>BB1</b>. On the basis of these theoretical results, the structure of black dye aggregation and the aggregation suppression mechanism by DCA during the immersion process to prepare for dye-sensitized solar cell (DSSC) are discussed