title: A photochemical on-off switch for tuning the equilibrium mixture of H2 nuclear spin isomers as a function of temperature.
abstract: The photochemical interconversion of the two allotropes of the hydrogen molecule [para-H(2) (pH(2)) and ortho-H(2) (oH(2))] incarcerated inside the fullerene C(70) (pH(2)@C(70) and oH(2)@C(70), respectively) is reported. Photoexcitation of H(2)@C(70) generates a fullerene triplet state that serves as a spin catalyst for pH(2)/oH(2) conversion. This method provides a means of changing the pH(2)/oH(2) ratio inside C(70) by simply irradiating H(2)@C(70) 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 pH(2)/oH(2) interconversion was observed for H(2)@C(60), which was rationalized by the significantly shorter triplet lifetime of H(2)@C(60) relative to H(2)@C(70).
authors.affiliation: Department of Chemistry, Columbia University, New York, New York 10027, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Frunzi
authors.forename: Steffen
authors.initials: S
authors.lastname: Jockusch
authors.forename: Judy Y-C
authors.initials: JY
authors.lastname: Chen
authors.forename: Rafael M
authors.initials: RM
authors.lastname: Krick Calderon
authors.forename: Xuegong
authors.initials: X
authors.lastname: Lei
authors.forename: Yasujiro
authors.initials: Y
authors.lastname: Murata
authors.forename: Koichi
authors.initials: K
authors.lastname: Komatsu
authors.forename: Dirk M
authors.initials: DM
authors.lastname: Guldi
authors.forename: Ronald G
authors.initials: RG
authors.lastname: Lawler
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Turro