A Stable Saddle-Shaped Polycyclic Hydrocarbon with an Open-Shell Singlet Ground State
J. Ma, J. Liu, M. Baumgarten, Y. Fu, Y. Z. Tan, K. S. Schellhammer, F. Ortmann, G. Cuniberti, H. Komber, R. Berger, K. Müllen, and X. Feng
Angewandte Chemie International Edition 12, 3280-3284 (2017)
Diindeno-fused bischrysene, a new diindeno-based polycyclic hydrocarbon (PH), was synthesized and characterized. It was elucidated in detailed experimental and theoretical studies that this cyclopenta-fused PH possesses an open-shell singlet biradical structure in the ground state and exhibits high stability under ambient conditions (t(1/2) = 39 days). The crystal structure unambiguously shows a novel saddle-shaped pi-conjugated carbon skeleton due to the steric hindrance of the central cove-edged bischrysene unit. UV/Vis spectral measurements revealed that the title molecule has a very narrow optical energy gap of 0.92 eV, which is consistent with the electrochemical analysis and further supported by density functional theory (DFT) calculations.