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Caption : figure s1. pressure dependences of the raman shifts (cm-1) of biphenylene at room temperature. 

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Caption : figure s2. pressure dependences of the infrared active modes (cm-1) of biphenylene at room temperature. 

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Caption : figure s3. infrared spectra of recovered biphenylene polymeric product from selected pressures.

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Caption : figure s4. evolution of corresponding compression ratio of lattice parameters from 0.9 to 25.0 gpa.

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Caption : figure s5. (a) variations of lattice parameters during compression, as determined from experiments (solid circles) and dft calculations (solid triangles). (b) pressure dependence of the unit cell volume of biphenylene. the black squares represent experimental results and the red circles represent dft calculations. the solid lines represent the fitting results of the 3rd order birch−murnaghan equation of state.

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Caption : figure s6. crystal structure of poly-bph at 300 k, simulated by molecular dynamic.

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Caption : figure s7. high-resolution transmission electron microscopy of poly-biphenylene.

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Caption : figure s8. matrix-assisted laser desorption ionization time of flight mass spectrometry (maldi-tof-ms) characterization of pe25 in the dichloromethane with the trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene] malononitrile (dctb) as matrix. the signals at m/z = 250, and 500 are the peaks of dctb clusters.