Observation of Triplet Intraligand Excited States through Nanosecond Step-Scan Fourier Transform Infrared Spectroscopy

Abstract

Nanosecond step-scan Fourier transform infrared spectroscopy permits the observation of triplet intraligand ((3)IL) 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.

Ligand-Localized Triplet-State Photophysics in a Platinum(II) Terpyridyl Perylenediimideacetylide

“…The FT-IR spectrum of 1 can be readily assigned by direct comparison to 3, which contains vibrations characteristic of the PDI portion of the complex (Figure 4, Table 2), namely, two peaks at 1695 and 1657 cm −1 due to the vibrations of the CO groups and a peak at 1598 cm −1 resulting from various vibrations of the PDI aromatic core, all in excellent agreement with previously reported spectra of the closely related 1,4,5,8-naphthalenediimide 120 and PNI. 114,115 The oscillator strength of the CC bond in 3 is too low to be observed in its FT-IR spectrum in solution. Similarly, 2 exhibits nearly identical infrared-active stretches emanating from the PDI acetylide moiety ( Figure 4, Table 2), including a CC vibration at 2091 cm −1 , two CO bands centered at 1692 and 1655 cm −1 , and delocalized PDI aromatic core vibrations at 1590 cm −1 .…”

Electron Storage Capability and Singlet Oxygen Productivity of a RuII Photosensitizer Containing a Fused Naphthaloylenebenzene Moiety at the 1,10‐Phenanthroline Ligand

“…[17,19,20,23,24] For instance, different types and number of methyl viologen,a nthraquinone, naphthalimide or pyrene derivatives hadb een introduced as an additional substituentt o2 ,2'-bipyridine (bpy) or 1,10-phenanthroline (phen). [23][24][25][26][27]28] The integration of donor-acceptor units like naphthalene dicarboxylic acid monoimide (NMI) or other rylene derivatives enablede asy synthetic access to photosensitizersw ith high thermala nd (photo)chemical stabilities and to adapt the photophysical as well as electrochemical properties of the chromophores in aw ide range. In addition, rylene dyes often provide high fluorescence quantum yields, large extinctionc oefficients over ab road spectralr ange and the option to store multiple electrons.…”

Probing the excited state nature of coordination complexes with blended organic and inorganic chromophores using vibrational spectroscopy

“…The evidence for the LC π,π* state was elegantly demonstrated using time-resolved infrared spectroscopy in the 1400 -1800 cm -1 region which showed that the transient created in [Ru(phen)2(PNI)] 2+ was identical to that from tolyl-PNI ( Figure 10). [177] In both cases the infrared bands from the imide carbonyl groups inform on the excited state. For tolyl-PNI the ground state bands at 1705 and 1657 cm Reprinted with permission from ref.…”