Cyclocarbon: smallest all-carbon electron acceptor
Recently synthesized C18 molecule demonstrates strong electron acceptor properties similar to the C60. In this work, we study computationally the ground and excited state properties of C18 and its complexes with several electron-donating molecules. We demonstrate that a high amount of the exact (HF) exchange in the DFT functional leads to a polyynic structure of C18, in agreement with experiment. We show that in complexes of C18 with electron donors, the lowest excited states are charge separated states formed by electron transfer to C18. This makes C18 to be the smallest all-carbon electron acceptor reported so far. Because C18 exhibits a larger internal reorganization energy as compared to fullerene C60, ET reactions with relatively high driving force will be shifted from the inverted to the normal Marcus regime when replacing C60 by C18.