Contributed talk

Bistability between open- and closed-shell states in a polycyclic conjugated hydrocarbon
S. Mishra¹, M. Vilas-Varela², L. Lieske¹, R. Ortiz³, S. Fatayer⁴, I. Rončević⁵, F. Albrecht¹, T. Frederiksen^3,6, D. Peña² and L. Gross¹

1 IBM Research Europe – Zurich, 8803 Rüschlikon, Switzerland
2 University of Santiago de Compostela, 15782 Santiago de Compostela, Spain
3 Donostia International Physics Center, 20018 Donostia-San Sebastián, Spain
4 Physical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), 23955-6900 Thuwal, Saudi Arabia
5 University of Oxford, Oxford OX1 3TA, United Kingdom
6 Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain

Indenofluorenes are non-benzenoid polycyclic conjugated hydrocarbons with unusual electronic properties, including low frontier orbital gaps, antiaromaticity and magnetism. In this contribution, the tip-induced synthesis of indeno[1,2-a]fluorene, the final and yet unreported indenofluorene isomer, will be shown [1]. On bilayer NaCl/Au(111) surface, indeno[1,2-a]fluorene is in the neutral charge state, while it exhibits charge bistability between neutral and anionic states on the lower work function bilayer NaCl/Ag(111) and Cu(111) surfaces. In the neutral state, indeno[1,2-a]fluorene exhibits either of two ground states: (1) an open-shell state, predicted to be a triplet by density functional theory and multi-reference calculations, or (2) a closed-shell state that exhibits bond length alternation characteristic of a para-quinodimethane moiety in the as-indacene core of the molecule. Switching between open- and closed-shell states of a single molecule is observed by changing its adsorption site on NaCl.

Figure 1: Molecular structure (top) and non-contact atomic force micrograph (bottom) of indeno[1,2-a]fluorene in the open- (left) and closed-shell (right) states.

[1] S. Mishra et al. arXiv:2303.04483 (2023).