Jesús Bello-García

Porphyrin polymers merge the photophysical, electrochemical, sensory and catalytic properties of porphyrins with the processability and robustness of polymeric materials, offering versatile and synergetic platforms for optoelectronics and catalysis. Here we report an on-surface strategy for the atomically precise polymerization of porphyrins via regioselective indenyl coupling. Deposition of an indenyl-functionalized porphyrin on Au(111) and sequential annealing drives a stepwise transformation: cyclodehydrogenation at 100 °C planarizes the precursor into π-extended porphyrins, while annealing above 125 °C triggers carbon–carbon homocoupling through five-membered moieties, forming short oligomers. Heating to 150 °C promotes chain growth into one-dimensional polymers with a 1.1 eV bandgap and extended π delocalization, alongside a minor fraction of cyclic trimers featuring a 1.1 eV HOMO–LUMO gap with both local and global aromaticity. The methodology also proceeds for Co-metallated precursors, confirming that indenyl coupling is also compatible for metalloporphyrins, establishing a general route to design π-extended porphyrin polymers.

The formation of non-planar PAHs from didehydro[8]annulene (COTyne) cycloadditions was investigated under both transition metal-catalyzed (Pd, Ru) and metal-free conditions. The observed reactivity depended on the planarity of the COTyne and the reaction conditions. Parent COTyne 1a dimerized into naphthocyclooctatetraene under TM-free conditions, whereas Pd(0) catalysis promoted its cyclotrimerization into benzotri[8]annulene 7. X-ray characterization and its dynamic behavior in solution was investigated. Planar dibenzoCOTyne 1b exhibited different reactivity depending on its formation method (in situ or preformed), the metal catalyst (Pd, Ru), and absence of catalysts. Under Pd(0) catalysis, cyclotrimerization yielded benzo-fused tri(dibenzo[8]annulene) 3 with moderate efficiency, regardless of how 1b was generated. The presence of K⁺ had no significant effect compared to tribenzoCOTyne 1c. Without metal catalysts, 1b predominantly formed the corresponding Dewar benzene 2. With Ru(II) catalysts, reactivity was influenced by both the generation method of 1b and the Cp ligand. When generated in situ, 1b was an inefficient ligand for CpRu, leading to Dewar benzene formation, whereas preformed 1b produced 3 in moderate yields. The competition between Dewar benzene and benzo-fused tri(dibenzo[8]annulene) formation increased with greater steric hindrance at the Ru center (CpRu vs. Cp*Ru catalysts). Dewar benzene formation likely proceeds via a cyclobutadiene intermediate followed by cycloaddition.