Unusual Low-Energy Near-Infrared Bands for Ferrocenyl–Naphthalimide Donor–Acceptor Dyads with Aromatic Spacer Groups: Prediction by Time-Dependent DFT and Observation by OTTLE Spectroscopy

Abstract

Time-dependent density functional theory (TDDFT) calculations for a series of donor−spacer−acceptor (D−S−A) molecules with phenyl (1), biphenyl (2), and anthryl (3) spacers interpolated between the ferrocenylalkene donor and −CC-4-naphthalimido acceptor components predicted the presence of weak, very low energy near-IR (NIR) transitions in the electronic spectra of the oxidized species Fc + −S−A. Subsequent optically transparent thin layer electrolysis (OTTLE) spectroscopy experiments in the spectral range 1500−3200 nm reveal that, in each case, very low energy NIR bands are indeed observed at approximately 2500 nm. The TDDFT calculations not only allow the prediction of these low energy bands but also, in concert with recently developed natural transition orbital (NTO) analysis, give detailed insights into the nature of the transitions involved. It is found that these bands around 2500 nm correspond to forbidden e 1 ″ → e 1 ″ transitions localized on the ferrocenium subunit with very low oscillator strengths.

How Hydrogen Bonds Affect Reactivity and Intervalence Charge Transfer in Ferrocenium‐Phenolate Radicals

“…However, the width, Δ$\tilde {\nu}$ 1/2 , of these bands is rather low and smaller than expected for IVCT transitions 40. These two low‐energy bands are fairly similar to those observed for NHR‐substituted ferrocenium ions such as [H‐3] ·+ [41a] and other substituted Fc + ions41b and have been attributed to Laporte‐forbidden d–d transitions of the ferrocenium moiety. To further confirm this assignment, a time‐dependent density functional theory (TD‐DFT) calculation [B3LYP/SV(P), COSMO CH 2 Cl 2 ] was performed for [1a] · , which provided low‐energy transitions at 2765, 2055, 1317, 1091, 997, and 771 nm (3617, 4865, 7594, 9168, 10031, and 12973 cm –1 , respectively; see Table S2 in the Supporting Information).…”

Synthesis of tetracyanoethylene‐substituted ferrocene and its device properties

“…Various kinds of organic compounds have been designed and synthesized including those with strong donor and acceptor groups in their structures. The most popular and efficient OPVs could be those involving donor–acceptor (D–A) type organic structures, because they have high charge mobility, more flexibility and more electrochemical stability …”

Redox Isomeric Ferrocenyl Styrylruthenium Radical Cations with Diphenyl-Substituted β-Ketoenolato Ligands

“…Hence, oxidized alkenylruthenium complexes display a prominent NIR absorption, which is due to a transition from the β-HOSO (the HOMO–1 of the neutral complexes) to the β-LUSO (the former HOMO). Both of these orbitals are delocalized over the entire π-conjugated metal-arylalkenyl backbone. ,− ,,,,,− However, ferrocenium ions with an attached π-conjugated aryl substituent also exhibit a fairly intense NIR band in a similar energy régime as has been pointed out by Simpson et al − Overlap of only one orbital of the set of two mutually mixed metal d π /d δ //Cp/ π/δ orbitals with the π-MOs of the corresponding substituent lifts the degeneracy of the two π and δ MOs and renders the otherwise symmetry-forbidden transition between the doubly occupied π orbital and the δ SOMO of the radical cations observable. In the present situation, the underlying band will most likely be associated with some charge transfer from the bridging ligand ,− and the remaining nonoxidized redox site to the oxidized one, such that its assignment as an intervalence charge-transfer transition (IVCT) seems appropriate.…”