Exact mass analysis of sulfur clusters upon encapsulation by a polyaromatic capsular matrix

Structural determination of inorganic clusters relies heavily on mass spectrometry because of, in most cases, their poor responsivities toward nuclear magnetic resonance, ultraviolet/visible, and infrared analyses. Nevertheless, mass spectrometry analysis of oligosulfurs (S-n), which are unique clusters with copious allotropic forms, usually displays their fragment peaks. Here we report that a polyaromatic capsule acts as a supramolecular matrix for the mass determination of the neutral sulfur clusters. Upon encapsulation, molecular ion peaks derived from the host-guest complexes including cyclic S-6 and S-8 clusters are exclusively detected by common electrospray ionization time-of-flight mass spectrometry analysis. Furthermore, mass spectrometry analysis of a cyclic S-12 cluster, which is in situ prepared from two S-6 clusters within the matrix upon light irradiation, is achieved by the same way. The present matrix can remarkably stabilize the otherwise labile S-6 and S-12 clusters in the polyaromatic shell not only under mass spectrometry conditions but also in an ambient solution state.