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.

Ryohei Kishi,Masayoshi Nakano,Masaki Yamane,Wataru Yoshida,Ryosuke Sugiura,Yosuke Shimizu

doi:10.1039/d0ra04787b

Ryohei Kishi, Masayoshi Nakano + Show 4 more

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https://doi.org/10.1039/d0ra04787b

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Abstract

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, nπ, in neutral [N]IF-CNB is 7N, and thus depending on N and charge states, nπ can be 4n + 2 and 4n. Quantum chemical calculations on neutral [6]IF-CNB and [8]IF-CNB and dicationic [8]IF-CNB2+ have revealed that they are expected to exhibit unique aromatic and open-shell characteristics depending on nπ, 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.

Highlights

Creation of p-conjugated oligomers with well-de ned cyclic structures, i.e., conjugated macrocycles, has been one of the hot topics in materials science.1 Owing to the cyclic topologies, the conjugation lengths of fully conjugated macrocycles are regarded as in nite, and this feature is re ected in their unique delocalized electronic structures
In the case of dicationic [8]IFCNB2+, we found one local minimum structure which belongs to the highest possible D4d symmetry
We have found from the analysis of gauge-including magnetically induced current (GIMIC) that magneticallyinduced current primarily originating in the p-electrons can ow over the belt along the curved p-surface, and as a result of the balance between the paratropic and diatropic contributions, [6]IF-carbon nanobelts (CNBs) is expected to exhibit global aromatic nature, even though the amplitudes of magnetically induced ringcurrent (MIC) density are weak compared to those of benzene

Summary

Introduction

Creation of p-conjugated oligomers with well-de ned cyclic structures, i.e., conjugated macrocycles, has been one of the hot topics in materials science.1 Owing to the cyclic topologies, the conjugation lengths of fully conjugated macrocycles are regarded as in nite, and this feature is re ected in their unique delocalized electronic structures. We theoretically investigate the aromatic and open-shell characteristics of carbon nanobelts (CNBs) composed of five- and six-membered rings.

Results

Conclusion