Carbon Nanohoops: Excited Singlet and Triplet Behavior of Aza[8]CPP and 1,15-Diaza[8]CPP.

The excited state properties of two nitrogen-doped cycloparaphenylene molecules, or carbon nanohoops, have been studied using steady-state and time-resolved absorption and emission spectroscopies. Quantum yield of fluorescence (Φf = 0.11 and 0.13) and intersystem crossing (Φisc = 0.45 and 0.32) were determined for aza[8]CPP and 1,15-diaza[8]CPP, respectively. We also present the proton transfer reaction between trifluoroacetic acid and the nitrogen-doped nanohoops, which resulted in significant modifications to the steady-state absorption and emission spectra as well as the triplet-triplet absorption spectra. From fluorescence quenching data we determine the equilibrium constant for the proton transfer reaction between aza[8]CPP (Keq = 1.39 × 10(-3)) and 1,15-diaza[8]CPP (Keq = 2.79 × 10(-3)) confirming that 1,15-diaza[8]CPP is twice as likely to be protonated at a particular concentration of trifluoroacetic acid.

Bending benzene: syntheses of [n]cycloparaphenylenes.

Since the first successful synthesis in 2008, methods to prepare the [n]cycloparaphenylenes have evolved rapidly. The aim of this synopsis is to provide an overview of recent advancements in this emerging field. The optoelectronic properties and supramolecular chemistry of these unique structures are presented as well.

Selective synthesis of strained [7]cycloparaphenylene: an orange-emitting fluorophore.

[n]Cycloparaphenylenes, which are short fragments of carbon nanotubes, have unique size-dependent optical properties. In this communication, we describe the first synthesis of [7]cycloparaphenylene ([7]CPP), the smallest cycloparaphenylene prepared to date. In order to access this structure, we have developed a synthetic route that capitalizes on successive orthogonal Suzuki-Miyaura coupling reactions. [7]CPP has 83 kcal/mol of strain energy and an orange emission at 592 nm.

Synthesis, Properties, and Design Principles of Donor-Acceptor Nanohoops.

We have synthesized a series of aza[8]cycloparaphenylenes containing one, two, and three nitrogens to probe the impact of nitrogen doping on optoelectronic properties and solid state packing. Alkylation of these azananohoops afforded the first donor-acceptor nanohoops where the phenylene backbone acts as the donor and the pyridinium units act as the acceptor. The impact on the optoelectronic properties was then studied experimentally and computationally to provide new insight into the effect of functionalization on nanohoops properties.

Theoretical analysis of [5.7](n)cyclacenes: closed-shell cyclacene isomers.

The [5.7](n)cyclacenes represent a novel class of all sp(2)-hybridized carbon structures. In contrast to the isomeric [n]cyclacenes, [5.7](n)cyclacenes are predicted at the B3LYP/6-31G* level of theory to have stable, closed-shell singlet ground state configurations. Predicted geometries, electronic structures, band gaps, nucleus-independent chemical shift (NICS) values, and strain energies for this new family of cyclic conjugated molecules are presented.