Extended Data Fig. 8: Simulations of the phonon band structures.

a−c, Simulated phonon bands corresponding to the experimentally observed 2050-cm⁻¹ mode, and d−f, 858-cm⁻¹ mode in 1a-EBPP (a,d), 3a-EBPP (b,e), and 5a-EBPP (c,f). In d−f, the dashed gray curves correspond to an almost degenerate mode of the 858-cm⁻¹ mode, which is not distinguishable in our experiment. Threefold and fivefold split subbands are clearly observed in 3a-EBPP and 5a-EBPP, respectively, with clear gap opening at the Γ point and the Brillouin zone edges. The freestanding 1a-EBPP structure is relaxed under vacuum, while 3a-EBPP and 5a-EBPP are relaxed on Ag(111) and Ag(100) substrates. Then, the metal substrates are removed, and the corresponding amounts of transferred charge are added to the polymer chains to simulate the phonon band structures.