Establishing symmetry-protected topological (SPT) phases with interactions in chemically realistic systems remains an open challenge. We show that a single, synthetically plausible organic one-dimensional chain, tunable via chemical modification of its radical sites, hosts two such phases: an even-Haldane phase of a dimerized S=12 Heisenberg chain and a Haldane phase of an S = 1 chain realized when Hund coupling locks two S=12 spins per monomer into S = 1. Density-functional theory places the active manifold deep in the Mott regime (U/t > 100), justifying a spin-only Heisenberg description; a compact (t,U) → J mapping then fixes exchange couplings. Exact diagonalization and DMRG reveal a consistent SPT fingerprint across both phases, including a quantized many-body Zak phase, even-degenerate entanglement spectrum, protected edge spins, and characteristic triplon-Haldane features in S+-(q,ω). Our results identify a chemically programmable molecular platform for interacting SPT physics in one dimension and suggest concrete spectroscopic routes to organic Haldane spin chains for nanoscale quantum devices.
Anindya et al. (Wed,) studied this question.