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