We designed and synthesized molecular tweezers consisting of nitrogen-embedded buckybowl subunits. The judicious choice of the covalent linkers modulated their binding strength with C60 or C70 in solution. Titration studies by optical and 1H NMR analyses revealed a 1:1 composition of the resulting complexes. X-ray diffraction analysis elucidated their solid-state structures, in which two azabuckybowl units surround one fullerene molecule. The large association constants stabilize the complexes toward redox reactions and the purification process on silica-gel column chromatography. The linker enabled tuning of the cavity size for binding of fullerenes, achieving complementary fullerene hosts for C60 and C70: the carbazole-bridged dimer preferentially associates with C70 over C60, while the phenanthrene-bridged dimer interacts with C60 more strongly than C70. Electrochemical analysis in combination with density functional theory calculations indicated the existence of intermolecular charge-transfer interactions between the buckybowl units and the fullerenes. Nonlinear optical measurements showed that the two-photon absorption cross sections of the molecular tweezers are enhanced upon association with fullerenes.
Bibliographical noteFunding Information:
This work was supported by a Grant-in-Aid for Young Scientists (A) (JSPS KAKENHI Grant JP16H06031) and by the Grants-in-Aid for Scientific Research on Innovative Areas “π-System Figuration” (2601) (JSPS KAKENHI Grants JP26102003 and JP15K21721), “New Polymeric Materials Based on Element-Blocks (2401)” (JSPS KAKENHI Grant JP15H00731), and “Coordination Asymmetry” (JSPS KAKEN-HI Grant 17H05363). S.H. acknowledges the Tokuyama Science Foundation for financial support. Y.H. acknowledges a Grant-in-Aid for JSPS Research Fellows (JP15J10528). Work at Yonsei University (Republic of Korea) was supported by the Global Research Laboratory (2013K1A1A2A02050183) through the National Research Foundation of Korea (NRF), funded by the Ministry of Science, ICT (Information and Communication Technologies), and Future Planning. This research was also partially supported by Graduate School of Yonsei University Research Scholarship Grants (2017).
© 2018 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry