Manipulating the electronic properties and structure of MoO3 nanosheets with light via an excited-state proton transfer mechanism

Light is an attractive source of energy to regulate stimuli-responsive chemical systems, enabling control over chemical and physical processes. Here, we use light as a gating source to control the redox state, the formation of a localized surface plasmonic resonance (LSPR), and the structure of molybdenum oxide (MoO3) nanosheets, which are important for a wide array of applications. However, the light excitation is not of the MoO3 nanosheets but rather of a pyranine (HPTS) photoacid, which in turn undergoes an excited state proton transfer (ESPT) process. We show that the ESPT process from HPTS to the nanosheets and the intercalation of protons within the MoO3 nanosheets triggers the reduction of the nanosheets and the formation of an LSPR peak, a process that is reversible, meaning that in the absence of light, the LSPR peak disappears and the nanosheets return to their oxidized form. We further show that this reversible process is accompanied by a change in the nanosheet size and morphology.