Size-Dependent Formation and Photophysical Properties of Ru(II) Supramolecules with Pyridyl Indolocarbazole

Extensive efforts in supramolecular chemistry have focused on employing ligands with fluorescence properties. In this study, a new dipyridyl indolocarbazole scaffold (ICzPy) was synthesized and, for the first time, employed in coordination-driven self-assembly with diruthenium (Ru) linkers (Ruox, Rubq, Runq, and Ruaq). Notably, selective formation of [1 + 1] or [2 + 2] assemblies was achieved depending on the type of di-Ru(II) linker: Rubq, Runq, and Ruaq yielded [1 + 1] assemblies, whereas Ruox (oxalate-linked di-Ru(II)) produced a [2 + 2] assembly. The geometric relationship between the dipyridyl indolocarbazole and di-Ru(II) units in the resulting assemblies was further investigated. The solid-state structures of the obtained supramolecules were confirmed using X-ray crystallography, revealing that long Ru linkers formed planar "□"-shape supramolecules, whereas short Ru linkers produced three-dimensional "["-shape supramolecules. The photophysical properties of both ICzPy and the Ru(II) assemblies were also examined. Notably, while ICzPy exhibited a moderately high photoluminescence quantum yield (PLQY), the PLQYs of the arene Ru(II) assemblies decreased sharply to below 2%, likely due to intramolecular photoinduced electron transfer from the ICzPy donor to the Ru acceptor unit.