The molecular-scale design of materials is one of the major frontiers in modern science. Flat, highly conjugated organic molecules are already used in advanced technologies such as chemical sensors, optoelectronic devices, and energy conversion systems. One of the most promising strategies to enhance their performance involves "linking" multiple units together, extending their electronic structure and thereby modifying their properties.
However, as these architectures grow in complexity, their synthesis becomes extremely challenging. In many cases, the molecules lose solubility and become nearly inaccessible through traditional solution-based methods. This limitation has hindered the construction of increasingly large and functional molecular structures for years.
Research led by Luis M. Mateo and Diego Peña at the Center for Research in Biological Chemistry and Molecular Materials (CiQUS) has overcome this barrier using a hybrid strategy. First, they synthesize carefully designed phthalocyanine units in solution. These units are then deposited onto a metal surface, where they react with each other to form a new extended structure composed of five cross-shaped, fused phthalocyanines. This approach combines the precision of classical solution chemistry with the possibilities offered by on-surface synthesis under controlled conditions.
"The surface not only facilitated the synthesis of the phthalocyanine pentamer but also enabled its sub-molecular resolution characterization using scanning probe microscopy," says CiQUS researcher Luis M. Mateo.
The result is a unique nanoarchitecture in which the five units function electronically as a single extended system. Experiments demonstrate that this connection significantly reduces the energy gap of the ensemble—a key property for charge transport and the development of advanced functional materials. Additionally, by leveraging the ability of phthalocyanines to coordinate metals in their central cavity, the design allows for the selective introduction of different metals at specific positions in the structure, adding new functionalities such as magnetism in the central core.
Diego Peña notes that the next step is to "modify the molecular precursor design to access two-dimensional polymers formed by phthalocyanines, a nanomaterial that will allow us to explore unique properties."
This work, developed under the MolDAM project (ERC Synergy Grant), is the result of close collaboration with the University of Regensburg (Germany) and IBM Research Europe–Zurich (Switzerland), combining advanced chemical synthesis and atomic-resolution microscopy. This breakthrough not only expands the possibilities of synthetic chemistry but also paves the way for designing even more complex two-dimensional materials with potential applications in molecular electronics, quantum technologies, and new energy devices.
CiQUS holds the CIGUS accreditation from the Galician Government (Xunta de Galicia), which recognizes the quality and impact of its research. It also receives financial support from the European Union through the Galicia FEDER 2021-2027 Program.
