Indolonaphthyridines (IND) are valuable chromophores with wide-ranging optoelectronic applications. Here, we present a new class of asymmetric IND derivatives, synthesised using novel high yielding methodology. We compare the absorption properties...

Singlet fission is a photophysical process that provides a pathway for more efficient harvesting of solar energy in photovoltaic devices. The design of singlet fission candidates is non-trivial and requires careful optimization of two key criteria: (1) correct energetic alignment and (2) appropriate intermolecular coupling. Meanwhile, this optimization must not come at the cost of molecular stability or feasibility for device applications. Cibalackrot is a historic and stable organic dye which, although it has been suggested to have ideal energetics, does not undergo singlet fission due to large interchromophore distances, as suggested by single crystal analysis. Thus, while the energetic alignment is satisfactory, the molecule does not have the desired intermolecular coupling. Herein, we improve this characteristic through molecular engineering with the first synthesis of an aza-cibalackrot and show, using ultrafast transient spectroscopy, that singlet fission is successfully “turned on.”

Singlet fission is a phenomenon that could significantly improve the efficiency of photovoltaic devices. Indolonaphthyridine thiophene (INDT) is a photostable singlet fission material that could potentially be utilised in singlet fission‐based photovoltaic devices. Here, we investigate the intramolecular singlet fission (i‐SF) mechanism of INDT dimers linked via para‐phenyl, meta‐phenyl and fluorene bridging groups. Using ultra‐fast spectroscopy we find the highest rate of singlet fission in the para‐phenyl linked dimer. Quantum calculations show the para‐phenyl linker encourages enhanced monomer electronic coupling. Increased rates of singlet fission were also observed in the higher polarity o‐dichlorobenzene, relative to toluene, indicating that charge‐transfer states have a role in mediating the process. We find the mechanistic picture of polarisable singlet fission materials, such as INDT, extends beyond the traditional mechanistic landscape.