Theoretical study on aromatic and open-shell characteristics of carbon nanobelts composed of indeno[1,2- b ]fluorene units: dependence on the number of units and charge states.

In this study, we theoretically investigate the aromatic and open-shell characteristics of carbon nanobelts (CNBs) composed of five- and six-membered rings. We have designed nanobelts composed of indeno[1,2- b ]fluorene ([1,2- b ]IF) units, which are referred to as [ N ]IF-CNB ( N : the number of five-membered rings). The number of π-electrons, n π , in neutral [ N ]IF-CNB is 7 N , and thus depending on N and charge states, n π can be 4 n + 2 and 4 n . Quantum chemical calculations on neutral [6]IF-CNB and [8]IF-CNB and dicationic [8]IF-CNB 2+ have revealed that they are expected to exhibit unique aromatic and open-shell characteristics depending on n π , there are several analogies of the electronic structures in [ N ]IF-CNB to those in [ N ]annulene. Delocalized and intermediate open-shell electronic structures of [ N ]IF-CNB are also useful to drastically change the third-order nonlinear optical properties. These results suggest that theoretically designed [ N ]IF-CNB can be attractive and challenging targets of organic synthesis for realizing novel open-shell functional conjugated macrocycles.