The selective and predictable synthesis of structurally uniform carbon nanotubes (CNTs) represents a long-standing goal in both nanocarbon science and synthetic organic chemistry. This Review focuses on synthetic studies toward the controlled synthesis of CNTs with single chirality through the organic synthesis of CNT segments and the organic template assisted growth of CNTs.

Cycloparaphenylenes (CPPs) are a remarkable class of hoop-shaped conjugated macrocycles with inimitable properties. Herein we describe a divergent synthesis of [7]CPP and [8]CPP. Furthermore we present the first crystal structure of [7]CPP. Thus, we have now established the size-selective synthesis of [n]CPP (n = 7-16) in a uniformed cyclohexane-based method.

The first synthesis of an all-benzene carbon nanocage 1, which represents a junction unit of branched carbon nanotubes, has been achieved. A stepwise assembly of six L-shaped units [cis-di(p-bromophenyl) cyclohexane derivative] and two three-way units (1,3,5-triborylbenzene) by cross-coupling and homocoupling provided the unstrained cyclic precursor. Acid-mediated aromatization of cyclohexane moieties in the precursor resulted in the formation of carbon nanocage 1. Photophysical measurements and DFT studies revealed the unique properties of 1, such as D 3 symmetry with degenerate HOMO/ HOMO À 1 and LUMO/LUMO + 1, high fluorescence quantum yield (F F ¼ 0.87), and a relatively large two-photon absorption cross section (500 GM at 590 nm), which are attractive for various applications.

The first size-selective synthesis of [9]- [11] and [13]cycloparaphenylenes (CPP) has been achieved by strategically utilizing cis-1,4-diphenylcyclohexane-1,4-diyl as the key terphenyl-convertible L-shaped unit. To access the designed triangular or rectangular macrocyclic precursors, we utilized palladiumcatalysed C-B/C-Br cross-coupling (Suzuki-Miyaura coupling) and/or nickel-mediated C-Br/C-Br coupling. We also established step-economical routes to [14] and [16]CPP using nickel-mediated C-Br/ C-Br coupling. The final aromatization steps toward CPPs were accomplished with NaHSO 4 . Thus, combined with our previous size-selective synthesis of [12] and [14]-[16]CPP, we completed our sizeselective synthesis of [9]-[16]CPP. The successful size-selective syntheses of [n]CPPs speak well for the flexibility and reliability of our strategy using a cyclohexane ring.

The first synthesis of a nitrogen-containing cycloparaphenylene, cyclo[14]paraphenylene[4]2,5-pyridylidene ([14,4]CPPy), has been achieved. A palladium-catalyzed stepwise assembly of 2,2'-bipyridine, benzene, and L-shaped cyclohexane units, followed by NaHSO(4)/o-chloranil-mediated aromatization, successfully provided [14,4]CPPy. While the absorption and fluorescence properties of [14,4]CPPy were somewhat similar to those of cycloparaphenylenes (λ(abs) = 344 nm, ε = 7.3 × 10(4) cm(-1) M(-1), λ(em) = 427 nm, Φ(F) = 0.80), it was found that [14,4]CPPy possesses an interesting halochromic property.