Reversible switching of light-gated organic transistors employing Dihydroazulene/Vinylheptafulvene photo-/thermochromic molecules

An innovative possibility to introduce additional functionality to organic field-effect transistors (OFETs) is to employ photochromic molecules, which undergo reversible isomerization under applied stimuli such as irradiation with specific wavelengths. As a result, the transistors not only can be switched on/off by the applied voltages, they can also be programmed by alternate triggers, such as light. Here, reversible switching of OFETs is presented by blending various dihydroazulene/vinylheptafulvene photoswitches into polythiophene-based conjugated polymers. In result, the transfer characteristics of the transistors are altered significantly through UV irradiation. In contrast to current literature on different photoswitches such as spiropyrans or diarylethenes, the backreaction is induced thermally and not via visible light irradiation and reproducibly yields the pristine transistor characteristics. This reversible switching upon alternating UV irradiation and thermal annealing is quantified by figures of merit such as the magnitude of drain current, threshold voltage, and subthreshold swing. Irradiating the devices with different doses of UV light shows that the magnitude of switching directly depends on the respective UV dose, hence enabling a multi-level electronic system. Furthermore, long-term cyclability over 100 steps of repeated UV light exposure and thermal annealing is demonstrated.