Inter-triplet spin–spin interaction effects on inter-conversion between different spin states in intermediate triplet–triplet pairs towards singlet fission

• Spin interaction between triplets determine the singlet fission process.
• Low magnetic field can enhance the dephasing of the spin precessions.
• High magnetic can facilitate the correlated spin precessions.

This article reports the experimental studies on the effects of inter-triplet spin interaction on singlet fission by using magnetic field effects of photoluminescence (MFEPL) based on tetracene. The MFEPL are compared for three different morphological states based on polycrystalline solid powder, amorphous solid film, and liquid solution. It is observed that the polycrystalline solid powder gives stronger MFEPL than that of amorphous solid film, while the liquid solution exhibits no detectable MFEPL. In essence, the MFEPL are determined by the inter-conversion between different spin states initiated by inter-triplet spin interaction through spin mixing in intermediate triplet–triplet pairs towards the singlet fission. The different MFEPL amplitudes suggest that the polycrystalline solid powder possesses an enhanced inter-triplet spin interaction in intermediate triplet–triplet pairs as compared to amorphous solid film. As a result, the enhanced inter-triplet spin interaction can cause a larger inter-conversion between different spin states in intermediate triplet–triplet pairs and consequently increases the singlet fission within polycrystalline structures. The absorption spectral characteristics and X-ray diffraction data confirm that the polycrystalline solid powder can indeed exhibits stronger intermolecular electronic interaction relative to amorphous solid film. Here, the stronger intermolecular electronic interaction provides an evidence for the enhanced inter-triplet spin interaction occurring within polycrystalline structures in the solid powder. Our experimental results indicate that increasing the inter-triplet spin interaction can boost the inter-conversion between different spin states in intermediate triplet–triplet pairs and consequently facilitates the singlet fission.

Figure optionsDownload as PowerPoint slide