Abstract
A phosphomolybdic acid/polyaniline (PMoA/PANI) optical-light photochromic inorganic/organic hybrid thin film was successfully synthesized by protonation between the the multiprotonic acid phosphomolybdic acid (H3PO4·12MoO3) and the conductive polymer polyaniline. The stable Keggin-type structure of PMoA was maintained throughout the process. Protonation and proton transfer successfully transformed the quinone structure of eigenstate PANI into the benzene structure of single-polarized PANI in the PMoA/PANI hybridized thin film, and proton transfer transformed the benzene structure of single-polarized PANI back to the quinone structure of eigenstate PANI in the PMoA/PANI hybrid thin film, as verified by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The average distribution of PMoA/PANI was observed by atom force microscopy (AFM). Interestingly, protonation of PMoA caused PANI to trigger transformation of the quinone structure into the single-polarized benzene structure, which enhanced the electron delocalization ability and vastly enhanced the maximum light absorption of the PMoA/PANI hybrid thin film as confirmed by density functional theory (DFT), electrochemistry, and ultraviolet-visible spectroscopy (UV-Vis) studies. Under optical-light illumination, the pale-yellow PMoA/PANI hybrid thin film gradually turned deep blue, thus demonstrating a photochromic response, and reversible photochromism was also observed in the presence of hydrogen peroxide (H2O2) or oxygen (O2). After 40 min of optical-light illumination, 36% of the Mo5+ species in PMoA was photoreduced via a protonation-induced proton transfer mechanism, and this proton transfer resulted in a structural change of PANI, as observed by XPS, generating a dominant structure with high maximum light absorption of 3.46, when compared with the literature reports.
Highlights
Photochromism is a unique physical-chemical phenomenon that is widely applied in various fields, such as information presentation [1], photodriven nanomachines [2], optical switching [3], optical memory devices and sensors [4,5,6], high-density optical-electron information storage [7], and molecular recognition or examination [8]
We explored the protonation effect of phosphomolybdic acid (PMoA) on PANI and the physical-chemical change of the PMoA/PANI hybrid film during the photochromic process through atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), electrochemical studies, ultraviolet-visible (UV-vis) spectroscopy and density functional theory (DFT) calculations, and these techniques were used to elucidate the photochromic mechanism of the PMoA/PANI hybrid film
The lowest unoccupied molecular orbital (LUMO) consisting of oFrFbiigigtuuarlrese8o8.n. ((atah))eDDrFFiTnTgccasaltlcrcuuullcaatttuiioornensseoxofhftithbheietFsFMπM*OOpssroooffpttehhreetieeeisigg.eeTnnhsstetaatFteeMPPAOANNcIaIlucununiltia.t.t(i(bob)n)DDpFrFToTvcciadallcecusullsaatttriiooonnnsgsooeffvtithdheeence thatFFtMhMeOOussnooiffptthoheleaurunPniipApooNllaaIrrpPPoAAsNsNeIIsusunenisti.ts.trong electron delocalization and transfer abilities via protonation of eigenstate PANI, which was demonstrated by the EIS test and confirmed the hypothesis that the PANAI/cPcMorodAinhgytboritdhiezimngecthhiannfiislmm eoxfhpibhiotstoicmhproromviesdmpfhoortoPcMhrooAmiacnpdrotpheertaipesp[li4c6a]t.ion of PANI, the mechanism photochromism of the PMoA/PANI hybrid thin film was attributed to IVCT and ligand-to-metal charge transfer (LMCT) [30] of PMoA and the change in electrical conductivity of PANI via protonation
Summary
Photochromism is a unique physical-chemical phenomenon that is widely applied in various fields, such as information presentation [1], photodriven nanomachines [2], optical switching [3], optical memory devices and sensors [4,5,6], high-density optical-electron information storage [7], and molecular recognition or examination [8]. We explored the protonation effect of PMoA on PANI and the physical-chemical change of the PMoA/PANI hybrid film during the photochromic process through atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), electrochemical studies, ultraviolet-visible (UV-vis) spectroscopy and density functional theory (DFT) calculations, and these techniques were used to elucidate the photochromic mechanism of the PMoA/PANI hybrid film. This characterization demonstrated that the protonation effect of PMoA on PANI played a significant role in enhancing proton conversion and the high maximum visible light absorbance of this photochromic material
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