1：Experimental Design and Method Selection:

The study involved synthesizing diarylethene derivatives with varying alkyl chain lengths and characterizing their photochromic properties using UV/Vis spectroscopy, HPLC, and X-ray crystallography. Theoretical models for photoisomerization were implied based on previous literature.

2：Sample Selection and Data Sources:

Four diarylethene compounds (1o-4o) were synthesized with methyl, ethyl, propyl, and butyl chains at the 2-position of thiophene rings. Samples were prepared in acetonitrile solution (2.0 × 10^-5 mol L^-1) and PMMA films (10% w/w).

3：0 × 10^-5 mol L^-1) and PMMA films (10% w/w). List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included Bruker AV400 NMR spectrometer, Bruker AmaZon SL Ion Trap Mass spectrometer, Bruker Vertex-70 IR spectrometer, PE CHN 2400 analyzer, WRS-1B melting point apparatus, Agilent 8453 UV/Vis spectrophotometer, SHG-200 UV lamp, CX-21 ultraviolet fluorescence analysis cabinet, BMH-250 visible lamp, Agilent 1260 HPLC, and Bruker Smart-Apex II CCD diffractometer. Materials included chemical reagents like THF, n-BuLi, dichloromethane, Na2SO4, petroleum ether, ethyl acetate, p-toluenesulfonic acid, acetone, pyridine, diethyl ether, acetonitrile, and PMMA.

4：Experimental Procedures and Operational Workflow:

Synthesis involved lithiation and condensation reactions followed by acid-catalyzed dehydration. Photochromic properties were measured by irradiating samples with UV (297 nm) and visible light (λ > 500 nm), recording absorption spectra, and analyzing photoconversion ratios and quantum yields. Fatigue resistance was tested by repeated irradiation cycles. X-ray crystallography was performed for structural analysis.

5：Data Analysis Methods:

Data were analyzed using UV/Vis spectrophotometry for absorption coefficients and wavelengths, HPLC for photoconversion ratios, and crystallographic software (SHELXS-2014 and SHELXL-2014) for structural parameters. Quantum yields were determined using a reference compound.