23 research outputs found
H‑Bonded Supramolecular Polymer for the Selective Dispersion and Subsequent Release of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes
Semiconducting, single-walled
carbon nanotubes (SWNTs) are promising
candidates for applications in thin-film transistors, solar cells,
and biological imaging. To harness their full potential, however,
it is necessary to separate the semiconducting from the metallic SWNTs
present in the as-synthesized SWNT mixture. While various polymers
are able to selectively disperse semiconducting SWNTs, the subsequent
removal of the polymer is challenging. However, many applications
require semiconducting SWNTs in their pure form. Toward this goal,
we have designed a 2-ureido-6[1<i>H</i>]-pyrimidinone (UPy)-based
H-bonded supramolecular polymer that can selectively disperse semiconducting
SWNTs. The dispersion purity is inversely related to the dispersion
yield. In contrast to conventional polymers, the polymer described
herein was shown to disassemble into monomeric units upon addition
of an H-bond-disrupting agent, enabling isolation of dispersant-free,
semiconducting SWNTs
Synthesis, Structure, and Binding Properties of Lipophilic Cavitands Based on a Calix[4]pyrrole-Resorcinarene Hybrid Scaffold
Light-Enhanced Fluorescence of Multi-Level Cavitands Possessing Pyridazine Upper rim
Completely different fluorescence behaviour of cavitands based on a same calix[4]resorcinarene compound was observed. While the fluorescence intensity of the parent compound, tetramethyl-cavitand (1) slowly faded as a result of UV-light exposure, the emission of the three level cavitand with pyridazine moieties at the upper rim (5a) was enhanced by the excitation in the UV-region. The structure of fluorescence emission (characterized by excitation-emission matrices) and the absorption of 5a remained unaltered. The analysis of fluorescence decay curves reveals the presence of two separated
components assigned to two individual emitting species.
The measured significant increase of the average lifetime
and quantum yield is the consequence of the UV-light induced transition between the different states of 5a. These observations can be explained by the structural difference between 5a and 1. As a counterpart of the naked cavitand (1) with methyl substituents at the upper rim only, 5a has three additional moieties benzene, triazole and pyridazine levels. Computational studies proved the existence of two conformational isomers of 5a. Upon ultraviolet light excitation a Bdark^ to Blight^ conformational transition occurs between the two isomers. This hypothesis was confirmed by anisotropy decay measurements