Spectrophotometric study of bridging N-donor ligand-induced supramolecular assembly of conjugated Zn-trisporphyrin with a triphenylamine core

Abstract

This article studies the supramolecular assembly behavior of a Zn-trisporphyrin conjugate containing a triphenylamine core (1) with bridging N-donor ligands using the UV-vis spectrophotometric titration method at micromolar concentrations. Our results show that pyridine, a non-bridging ligand, formed a 3:1 open complex with 1. The corresponding binding constant was estimated to be (2.7 ± 0.15) × 1014 M−3. In contrast, bridging ligands, 4,4-bipyridine (BIPY) and 1,3-di(4-pyridyl)propane (DPYP), formed stable 3:2 double-decker complexes with 1 in solution, which collapsed to yield a 3:1 open complex when excess BIPY or DPYP was added. The binding constants for forming BIPY and DPYP double-decker complexes were estimated to be (9.26 ± 0.07) × 1027 M−4 and (3.62 ± 0.16) × 1027 M−4, respectively. The UV-vis titration profiles supported the conclusion that the degradation of the 3:2 double-decker 1·BIPY complex is less favorable compared to that of 1·DPYP. Consequently, the formation of the 3:1 1·DPYP open complex proceeded more readily than that of 1·BIPY.