Electrically driven singlet-triplet transition in triangulene spin-1 chains

Recently, graphene triangulene chains have been synthesized, and their magnetic response has been analyzed by scanning tunneling microscopy methods by Mishra et al. [Nature (London) 598, 287 (2021)]. Motivated by this study, we determine the exchange bilinear and biquadratic constants of the triangulene chains by calculating two-spin rotations in the spirit of the magnetic force theorem. We then analyze open-ended, odd-numbered chains, whose edge states pair up forming a triplet ground state. We propose three experimental approaches that enable us to trigger and control a singlet-triplet spin transition. Two of these methods are based on applying a mechanical distortion to the chain. We finally show that the transition can be controlled efficiently by the application of an electric field.