Effect of Long-Lived Ground-State Diradicaloids on the Photophysics of Semiladder Thiophene-Based Polymer Aggregates for Organic Light-Emitting Transistor Applications

To fully utilize the immense potential of organic light-emitting transistors (OLETs), the mechanism of charge transfer in these devices needs to be better understood. The majority of prior studies have leaned toward understanding either organic light-emitting diodes (OLEDs) or organic field-effect transistors. Recently, there has been an interest in the use of open-shell structures, which have been reported to enhance the spin density that is delocalized along the planar π-conjugated backbone, ultimately affecting their charge transfer and the overall device performance efficiency. These structures tend to have low-lying triplets and small singlet–triplet energy gaps, which are favorable for charge and energy transfer for OLET applications. Open-shell diradicals have been reported to enhance the efficiency of OLEDs by offering intermolecular spin–spin interactions, which lead to σ-aggregation. This σ-aggregation eventually leads to the formation of σ-polymerization, affecting intermolecular stacking and charge transport, which has been useful for OLEDs. However, it is unknown how diradical states affect the efficiency of OLETs. In this study, we utilize both linear and nonlinear spectroscopic techniques to probe the dynamics of diradical states in novel organic thiophene systems. We also utilize computational methods to probe the energies of the electronic states of the diradical systems investigated. For the furan-containing polymer system, we found the formation of long-lived zwitterions. We propose that the formed diradical character with a lifetime of 25 μs lowers the charge transport in the resonant structures, reducing charge transfer and negatively affecting the external quantum efficiency of the thiophene-based OLETs.