Fused Hexabenzocoronene-Porphyrin Conjugates with Tailorable Excited-State Lifetimes

A new clear-cut strategy for fusing N-heterocyclic and carbon-pure systems is introduced en route to a versatile platform of multi-purpose tetrapyrrolic chromophores. In particular, three novel C-C bond-fused porphyrin-hexabenzocoronene (HBC) conjugates were synthesized under oxidative cyclodehydrogenation conditions, starting from tailor-made nickel porphyrin precursors. The fusion of the individual aromatic systems via 5-membered rings led to highly soluble pi-extended porphyrins in excellent yields. The resulting porphyrin-HBC conjugates exhibit absorption cross-sections that are of interdisciplinary interest in the ever-growing field of organic photovoltaics and near-infrared (NIR) dyes. Quantum chemical calculations show that the newly formed 5-membered rings induce biradicaloid character in the porphyrin core, which has a strong impact on excited state lifetimes. This is confirmed by a thorough optoelectronic and time-resolved characterization in order to understand these unique features better. Broadened absorption characteristics go hand-in-hand with short-lived excited states with up to six orders of magnitude faster decay rates. The synthesis of three novel C-C bond-fused porphyrin-hexabenzocoronene (HBC) conjugates is presented. By connecting the aromatic systems of the macrocycles via 5-membered rings under standard Scholl conditions, the formation of highly soluble and stable pi-extended porphyrins is achieved. The described planarization led to significant alterations regarding the photophysical and optoelectronic characteristics of the molecules. image