Stabilizing Diketopyrrolopyrrole Radical Cations Through Carbazoles: Substitution Pattern vs Spin Delocalization

The synthesis of organic radicals continues to garner significant interest due to their fascinating optical, electronic, and magnetic properties. Moreover, the growing demand for chemically stable organic radicals is driven by the rapid expansion of the market for electronic devices utilizing organic semiconductors. In this context, the development of multifaceted approaches for the design of stable organic radicals is of great importance. In this work, we introduce a strategy for generating stable radical cations of diketopyrrolopyrroles (DPP) by modulating the substitution pattern of the electron-donating carbazole substituent. Using electronic, spin resonance, and vibrational spectroscopies, supported by density functional theory, we carefully investigated the electronic structures and chemical stability of the DPP radical cations. Our findings demonstrate that the position of electron-rich heteroatoms and the presence of Clar's aromatic sextets in donor moieties play a pivotal role in enhancing the chemical stability of DPP radical cations.