Direct Observation of a Triplet-State Absorption-Emission Conversion in a Fullerene-Functionalized Pt(II) Metallacycle

Abstract

An interesting triplet excited-state absorption-emission conversion of a fullerene-functionalized Pt(II) metallacycle (C 60 –Pt) caused by a concentration effect was directly observed by nanosecond transient absorption (ns TA) spectroscopy. In dilute solution, the triplet excited-state absorption (TESA) band was observed at about 750 nm with a lifetime of ca. 10.7 μs. However, with increasing the concentration, the absorption band converted to a triplet excited-state emission (TESE) band with a longer lifetime of ca. 15.4 μs. Femtosecond transient absorption experiments and quantum chemistry calculations were performed to reveal the excited-state decay pathways of C 60 –Pt in concentrated solution. This conversion was ascribed to the formation of a triplet excimer, which forms at localized 3C60 * states. This work demonstrates that radiative excimers with longer-lived triplet excited states can exist in concentrated solution, and this finding will provide useful information for applications of fullerene complexes, especially as photosensitizers.