A Photochemical On–Off Switch for Tuning the Equilibrium Mixture of H2 Nuclear Spin Isomers as a Function of Temperature

• Published in: Journal of the American Chemical Society Vol. 133; no. 36; pp. 14232 - 14235
• Main Authors: Frunzi, Michael, Jockusch, Steffen, Chen, Judy Y.-C, Calderon, Rafael M. Krick, Lei, Xuegong, Murata, Yasujiro, Komatsu, Koichi, Guldi, Dirk M, Lawler, Ronald G, Turro, Nicholas J
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14.09.2011
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja206383n

The photochemical interconversion of the two allotropes of the hydrogen molecule [para-H2 (pH2) and ortho-H2 (oH2)] incarcerated inside the fullerene C70 (pH2@C70 and oH2@C70, respectively) is reported. Photoexcitation of H2@C70 generates a fullerene triplet state that serves as a spin catalyst for pH2/oH2 conversion. This method provides a means of changing the pH2/oH2 ratio inside C70 by simply irradiating H2@C70 at different temperatures, since the equilibrium ratio is temperature-dependent and the electronic triplet state of the fullerene produced by absorption of the photon serves as an “on–off” spin catalyst. However, under comparable conditions, no photolytic pH2/oH2 interconversion was observed for H2@C60, which was rationalized by the significantly shorter triplet lifetime of H2@C60 relative to H2@C70.