Synthesis, Optoelectronic, and Photoelectrochemical Properties of an Azulene-Bridged Porphyrin Dimer

Although azulene-incorporated porphyrin analogues, referred to as ″azuliporphyrins”, are well documented in the literature, the studies available on covalently tethered azulene–porphyrin hybrid molecules are limited. This work reports the synthesis of 1,3-azulene-bridged porphyrin dimers 3 and 4, achieved through the Suzuki–Miyaura cross-coupling reaction. The optoelectronic properties, photophysical behavior, excited-state dynamics, and potential application of dimer 4 in photoelectrochemical water splitting (PEC-WS) are investigated. Dimer 4 exhibits a smaller HOMO–LUMO gap and a lower ionization potential than the corresponding monomer 5. However, despite having an extended π-conjugation, the V-shaped geometry of the dimer restricts its long-range aggregation and charge/exciton delocalization in comparison to its corresponding monomer. The computational electronic structure analysis complements the experimental findings. The results presented in this paper provide rational insights into the structure–property correlation within the less explored azulene–porphyrin hybrid systems.