BN isosterism, a strategy based on the substitution of C=C double bonds by boron-nitrogen (B-N) units in polyaromatic structures, allows for the modulation of a series of critical physical properties of these molecules, such as electron mobility and reorganization energies between reactive species. These characteristics make these compounds particularly attractive platforms for the design of next-generation organic semiconductors. However, despite their potential to revolutionize optoelectronics, their practical application has been hindered for decades by the intrinsic complexity of synthesizing these molecules efficiently, and doing so on a large scale.
Dr. Federica Rulli defended her doctoral thesis at IQS, in which she developed new synthetic methodologies to obtain BN-doped aromatic structures, systems that present new and attractive optoelectronic and semiconducting properties.
In the Department of Organic and Pharmaceutical Chemistry at IQS, one of the research lines of the CRISOL group – Chemical Reactions for Innovative Solutions – is the development of cutting-edge synthetic methodologies for obtaining boron and nitrogen doped polyaromatic compounds as a platform for the design of new organic semiconductors. The group’s goal is twofold: to overcome historical challenges in the synthesis of these structures, while deepening their photophysical characterization, thus allowing the design of materials with new and attractive semiconducting properties.
Within this framework, Dr. Federica Rulli’s doctoral thesis, entitled New routes to BN Embedded Polyaromatics, explored new synthetic methodologies based on the 4a,8a-azaboranaphthalene ring, a structure that constitutes a versatile platform for developing new BN-doped polycyclic aromatic hydrocarbons (PAHs). The main objective was to optimize the synthesis of the BN-naphthalene core and to develop more complex structures derived from it.
The thesis was directed by Dr. Ana Belén Cuenca González and Dr. Raimon Puig de la Bellacasa Cazorla, within the framework of the BISiBonds project.
Optimization of BN-naphthalene synthesis and exploration of new synthetic routes
Through a meticulous reevaluation of existing routes, Dr. Rulli identified that the main “bottleneck” was the final dehydrogenation step, historically inefficient and critical. The fundamental innovation of this work lies in the use of norbornene as a highly effective hydrogen acceptor. This advance, added to the development of a new protocol for obtaining the key intermediate – the result of a collaboration with Guillem Sanz, a researcher from the BISiBonds team at the Institute of Advanced Chemistry (IQAC) -, has allowed the transformation of a previously problematic process into the most efficient synthetic route reported to date for the BN-naphthalene core.
Another major methodological development of this thesis has been the application of cooperative Palladium-Norbornene catalysis of the Catellani type to the synthesis of new BN-extended structures. In this sense, various annulative transformations were carried out that allowed the construction of doped PAHs of the BN-phenanthridines and BN-fluorenones type, among others, which led to the synthesis of an extensive family of BN-polyaromatic compounds.
Photophysical characterization and optoelectronic properties
In collaboration with Dr. Roger Bresolí and Dr. Santi Nonell from the AppLightChem research group at IQS, Dr. Rulli carried out the photophysical characterization of the resulting BN-PAHs, revealing the profound influence of the incorporation of BN units on their optoelectronic properties. Thus, BN-doping modulates both the absorption and emission profiles of the compounds obtained, as well as their redox behavior. Of particular interest is that the orientation of the BN vector in some benzofluorenone prototypes exerts a great influence on the capacity of these molecules to generate singlet oxygen.
Development of more complex structures
Dr. Rulli’s thesis also allowed the preparation of a series of BN-naphthalenes functionalized with metalloids (B, Si or Sn) regioselectively at the a positions of the BN bond. Some of these compounds demonstrated transmetalation capability to iodane-type species, leading to the first BN-diaryliodonium salt, which opens a new route for the functionalization of the BN core and establishes a conceptual link between BN isosterism and hypervalent iodine chemistry
Related Publications
Federica Rulli et al, From propenolysis to enyne metathesis: tools for expedited assembly of 4a,8a-azaboranaphtalene and extended polycycles with embedded BN, Chem Sci, 15, 2024
Federica Rulli et al, Catellani-Inspired BN-Aromatic Expansion: A Versatile Tool toward π-Extended 1,2-Azaborines with Tunable Photosensitizing Properties, J. Am. Chem. Soc. 2026, 148, 3, 3614–3625
This thesis has been carried out within the framework of the project Use of main group elements as a springboard for the development of chemical concepts, emerging reactivities and new molecular architectures (BISiBonds), within the State Plan for R+D+i Projects 2023 of the Ministry of Science and Innovation / State Research Agency.
COLLABORATORS
Research Groups
CRISOL – Chemical Reactions for Innovative Solutions
CRISOL is a powerful team capable of offering innovative chemical tools that make it real solutions to the challenges of Molecular Science, a discipline that is at the heart of key activities for Society, such as Medicinal and Process Chemistry, or Materials Science.
GQF – Pharmaceutical Chemistry Group
The GQF group research focuses on two main areas: 1) The Pharmaceutical Chemistry Unit (new drugs)2) The Continuous Chemical Processes Unit
