Tio2 particles

We fabricated pp-PSP in three steps: First, the poly(4tBS) (poly(4-tert-butyl styrene), Sigma Aldrich, St. Louis, MO, USA) toluene solution with a concentration of 8.1 g/L was prepared. This solution of 3.0 mL was sprayed onto an aluminum plate (20 × 20 mm) as a base layer. Second, the ethanol solution of polymer particles (polymer particle: ethanol = 30 mg: 10 mL) was sprayed onto the base layer. Lastly, the ethanol solution of PtTFPP (platinum (II) meso-tetra(pentafluorophenyl) porphine, Frontier Scientific, Logan, UT, USA) with a concentration of 1.4 × 10⁻² g/L was sprayed onto the polymer particle layer (the PtTFPP solution of 5.0 mL was sprayed). In between each step, the layer was dried for about 8 h to remove the solvents. The arithmetic average roughness of the fabricated pp-PSP surface was measured as $R_{\mathrm{a}}=0.93 \mathsf{\mu }\mathrm{m}$ by a laser microscope (VK-X200, Keyence, Osaka, Japan). This is equivalent to the diameter of the polymer particles.
We also fabricated PC-PSP to compare the photostability following the same procedure as pp-PSP except the use of TiO₂ particles (Sigma Aldrich, St. Louis, MO, USA) instead of employing polymer particles. We prepared 5 samples each for pp-PSP and PC-PSP.

The images of coated and uncoated fiber surfaces were obtained by a SEM (JSM-6700F, JEOL) and an AFM (Dimension 3100, Digital Instruments). The cross-sections were prepared by a FIB following a standard preparation method³⁸ (details in Supplementary Method B), before characterization by a TEM (JEM-100CXII, JEOL). The cross-sections were also characterized and confirmed by a 3D surface optical profilometer (Wyko NT 3300, Veeco). The TiO₂ layer masses (m_TiO2) on the optical fibers were measured gravimetrically by the weight of the optical fibers before and after the dip-coating/drying cycles. The porosity of the TiO₂ coating layers, which is defined as the fraction of the total pore volume over the volume of the TiO₂ layer, was calculated using Eq. (9). $\mathrm{Porosity}=1-\frac{m_{\mathrm{TiO}2}}{{\rho }_{\mathrm{TiO}2}\mathrm{\cdot }L\mathrm{\cdot }\pi d\mathrm{\cdot }D}$ where ρ_TiO2 is the true density of the TiO₂ particles (4.26 g/mL at 25 °C obtained from Sigma-Aldrich), L is the TiO₂ coating length, d is the diameter of optical fibers, and D is the thickness of the TiO₂ coating layers, which was determined by the cross-sectional profiles of TiO₂-QOFs from SEM images. The TiO₂ patchiness was calculated by dividing the optical fiber surface in direct contact with TiO₂ nanoparticles by the total surface of the optical fiber determining from TEM cross-section images.