Porphyrins are a class of representative Hückel aromatics with exceptional properties. Their central macrocycle is composed of tetrapyrrole rings connected by methine groups. This 18π electron conjugated delocalized system not only exhibits high stability but also has demonstrated excellent photophysical properties. However, the intrinsic blank between the B and Q bands limits the light-harvesting ability of the porphyrins for applications. An efficient approach for enhancing the light-absorbing capability involves connecting porphyrins with other extensive π-systems through multiple covalent bonds, thereby promoting enhanced electronic interaction among the constituent units and shrink the optical bandgaps.

Carbolong complexes, which mean n-atom unsaturated carbon chain chelates to a transition metal, are a series of novel metallaaromatics developed by Prof. XIA Haiping. Osmapentalynes featuring Craig aromaticity are one of the representative carbolong complexes. The formation of this d_π-p_π conjugated complexes occur through the insertion of a transition metal into the π- conjugated system, distinguishing them from the traditional p_π-p_π conjugated system and resulting in distinct physical properties. Osmapentalynes exhibit broad and strong absorption and show wide applications such as homogeneous catalysis, photoluminescence, organic/perovskite solar cells, biomedicine, and photothermal seawater desalination.

In this thesis, the research was primarily focused on the construction of large π conjugated systems, incorporating Hückel aromaticity of porphyrins and Craig aromaticity of osmapentalynes, in order to enhance the light-harvesting capabilities of both porphyrins and osmapentlaynes. The research involved the synthesis of a range of porphyrin-based carbolong model complexes, oligomers, and polymers, with a focus on investigating their properties and exploring the potential applications. The thesis is divided into the following five chapters:

In Chapter 1, the structures, photophysical properties, and applications of porphyrins are briefly introduced. Additionally, a strategic approach for enhancing the absorption characteristics of porphyrins was also presented. Moreover, the concepts of metallaaromatic complexes were emphatically reviewed. The synthesis and reactivity of metallaaromatic carbolong complexes, as well as their applications were also summarized.

In Chapter 2, an efficient coupling reaction between C≡C bond of meso-diethynylated- porphyrin and the M≡C bond of osmapentalynes in the presence of oxidant were studied. These newly discovered reactions exhibited remarkable efficiency, allowing for direct conjugation of Hückel aromatic porphyrins and Craig aromatic osmapentalynes through acetylene linkers. The resulting porphyrin-carbolong hybrids exhibited remarkably broad and intense absorption across the UV-Vis-NIR region. Moreover, resulting d_π-p_π conjugated materials displayed promising applications in the field of biomedicines.

In Chapter 3, the above coupling reactions of C≡C bond and M≡C bond have been further developed as a polymerization methodology for constructing a series of conjugated metallaaromatic-containing polymers. The resulting porphyrin-based polycarbolongs exhibited good stability and solubility, broad and strong UV-Vis-NIR absorptions, diverse energy levels and narrowed optical bandgaps, which have potential for many applications. The low-energy absorption band observed in porphyrin-based polycarbolongs can be primarily attributed to the significant d_π-p_π conjugation. Notably, the porphyrin-based polycarbolongs displayed superior photothermal effects than the corresponding model compound under the same test conditions, which show potential applications in biomedicine fields.

In Chapter 4, an alternative efficient metal-involved triple bond polymerization (MTP) was employed to construct porphyrin-based polycarbolongs. The resulting polycarbolong with a free-base porphyrin component can be further modified with various metal ions, including Zn²⁺, Cu²⁺ and Co²⁺, to form metalloporphyrin-based polycarbolongs. The metallization process of porphyrin-based polycarbolongs has been demonstrated to be highly efficient, and was comprehensively investigated by model and dimer compounds. The metallization of polycarbolongs provided a facile access to obtain conjugated polymers with a broad range of energy levels and narrowed optical bandgaps. Consequently, the resulting metalloporphyrin- based polycarbolongs exhibited strong panchromatic absorption spanning from 300-900 nm and displayed promising performance in the field of biomedicine.

In Chapter 5, we summarize the research work and give a prospect of this thesis.