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.