Nanosecond step-scan Fourier transform infrared spectroscopy permits the observation of triplet intraligand (3IL) character in the excited states of [Ru(bpy)2(PNI-phen)]2+ and [Ru(PNI-phen) 3]2+ where PNI is 4-piperidinyl-1,8-naphthalimide. After pulsed 355-nm laser excitation, the two ground-state imide C=O bands in each compound are bleached and two substantially lower energy vibrations are produced; the lower energy feature appears as two distinct bands split by an overlapping transient bleach. Model studies confirm that the time-resolved vibrational data are consistent with photoinduced sensitization of the 3IL excited state. Density functional theory calculations also support these assignments because localization of triplet electron density on the PNI moiety is expected to lead to red-shifted C=O vibrations of magnitude similar to those measured experimentally. The current results illustrate that triplet electron density can be directly tracked by time-resolved infrared measurements in metal-organic chromophores and that frequency shifts comparable to those observed in charge-transfer systems can be realized.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry