The recent synthesis 1 of H 2 @C 60 and D 2 @C 60 has provided photochemists with an opportunity to investigate whether the simplest molecule, H 2 , incarcerated inside a fullerene, can communicate with the electronically excited walls of its fullerene container and with excited molecules in the "outside world". 2 We report investigations comparing the photophysical characteristics of triplet C 60 and triplet H 2 @C 60 and the quenching of singlet molecular oxygen, 1 O 2 by C 60 , H 2 @C 60 , and D 2 @C 60 . For comparison, the quenching of 1 O 2 by H 2 and D 2 in solution is reported for the first time. Although the interactions of hydrogen with the walls of triplet C 60 were found to be too weak to be determined by either triplet-triplet absorption or EPR spectroscopy, we report a significant interaction between singlet molecular oxygen ( 1 O The interaction of incarcerated H 2 and D 2 with the walls of triplet fullerene was examined by laser flash photolysis, employing pulses from a Nd:YAG laser (532 nm, ∼5 ns pulse width). C 60 shows a triplet-triplet absorption centered at 747 nm, which was utilized to determine the triplet lifetimes of C 60 , H 2 @C 60 , and D 2 @C 60 in benzene solutions. No differences in the triplet lifetimes were observed within our experimental error (τ ) 110 ( 8 µs; for further details see Supporting Information). Thus, the interaction of incarcerated H 2 and D 2 with the paramagnetic walls of the triplet fullerene is too weak to be determined by triplet lifetime measurements.The magnitude of the interaction of incarcerated H 2 and D 2 with the triplet fullerene was also examined by time-resolved EPR (TREPR). TREPR spectra and transient decay kinetics of C 60 , H 2 @C 60 , and D 2 @C 60 were studied in benzene, toluene, and methylcyclohexane at 285 K. No differences in the spectra and transient decay kinetics of 3 C 60 , H 2 @ 3 C 60 , and D 2 @ 3 C 60 were found.Although there was no measurable interaction of incarcerated H 2 or D 2 with the triplet walls of C 60 , we searched for an interaction with the incarcerated H 2 and D 2 with an external electronically excited molecule, singlet molecular oxygen, 1 O 2 .Large differences in the quenching of 1 O 2 by H-X and D-X bonds are well-known. 3 To the best of our knowledge, there are no reports of the rate constants for quenching of 1 O 2 by H 2 or D 2 in solution, although a large isotope effect is found in the gas phase. 4 It was therefore of interest to determine the quenching rate constants of 1 O 2 by H 2 and D 2 in solution and to compare these rate constants with those for H 2 @C 60 and D 2 @C 60 in solution.The absolute quenching rate constants of 1 O 2 by H 2 @C 60 and D 2 @C 60 were determined using a time-resolved method, employing the host, C 60 , which is known to be an efficient 1 O 2 sensitizer. 5 CS 2 was selected as solvent based on the relatively long lifetime of 1 O 2 (τ ) 79 ms) 6 and high solubility of C 60 in CS 2 (7.9 mg/ mL). 7 The 1 O 2 quenching was monitored by its characteristic phosphorescence at 1270 nm. ...
