Nanowires and Molecular Dyes for Artificial Light-Driven Synapses and Neurons

Sammanfattning

The development of neuromorphic computing requires devices that can use low power consumption and highly parallel architecture to process and store information, similar to the biological nervous systems. Molecular photoswitches, especially Donor–Acceptor Stenhouse Adducts (DASAs), offer a promising platform for such applications, because they undergo reversible, light-driven structural changes and show wavelength-dependent optical responses. However, to transform their molecular behavior into functional device structures, it is necessary to have a deeper understanding of how these molecules interact with nanostructure substrates, and how their optical and electrical signals evolve under controlled illumination. This thesis studies the properties of DASA molecules AP-048 and AP-066 on both sapphire substrates and InP nanowire arrays. First, their bleaching and recovery dynamics were examined in solution and thin films to establish baseline behavior and to evaluate how casting conditions affect optical stability. Then, mixed-dye films were studied under dual-wavelength illumination to assess whether independent channels could be defined in a single molecular layer. The results show that although the spectral overlap is relatively small, the two dyes can still maintain a distinguishable response under selective excitation, and a small spectral overlap may introduce a weak additional modulation. When integrated with vertical InP nanowire arrays, the DASA layer exhibits enhanced signal amplitude and clear photogenic electrical signal reading. By combining green and red Write/Read pulses, four different readout channels can be distinguished. Channels directly exposed to the writing wavelength display exponential decay and recovery, which is consistent with the reversible photochemical kinetics. In contrast, the indirect channels only show very small, almost linear changes. These weak residual changes are more in line with optical scattering, moderate spectral overlap, or measured background drift. According to current data, they cannot be directly attributed to molecular transitions. The comparison highlights that the dual-dye system can tolerate the slight cross-effect inherent in broadband lighting while maintaining the independence of the functional channel. Overall, these results demonstrate that DASA-nanowire device provides a viable platform for multi-wavelength optical memory and synaptic-like functions. The combination of fast and slow response of AP-066 and AP-048 provides a variety of time dynamics in a hybrid system, suggesting the potential for scalable photonic neuromorphic devices. Future improvements may include optimizing molecular alignment, using a narrower-band excitation source, and designing nanowire geometry to further reduce crosstalk and improve device performance.