Molecular Engineering of Intensely Near-Infrared Absorbing Excited States in Highly Conjugated Oligo(porphinato)zinc−(Polypyridyl)metal(II) Supermolecules

Authors:
Publisher website
Google Scholar
Abstract
A new series of chromophores, MPZn n, which combine ethyne-bridged bis(terpyridyl)metal(II)−(porphinato)zinc(II) (MPZn) and oligomeric, ethyne-bridged (porphinato)zinc(II) (PZn n) architectures, have been synthesized and characterized, along with a series of derivatives bearing pyrrolidinyl electron-releasing groups on the ancillary terpyridine units (Pyr m MPZn n). Cyclic voltammetric studies, as well as NMR, electronic absorption, fluorescence, and femtosecond pump−probe transient absorption spectroscopies, have been employed to study the ground- and excited-state properties of these unusual chromophores. All of these species possess intensely absorbing excited states having large spectral bandwidth that penetrate deep in the near-infrared (NIR) energy regime. Electronic structural variation of the molecular framework shows that the excited-state absorption maximum can be extensively modulated [λmax(T1 → Tn)] (880 nm < λmax < 1126 nm), while concomitantly maintaining impressively large T1 → Tn absorption manifold spectral bandwidth (full width at half-maximum, fwhm, ∼2000−2500 cm-1). Furthermore, these studies enable correlation of supermolecular electronic structure with the magnitude of the excited-state lifetime (τes) and demonstrate that this parameter can be modulated over 4 orders of magnitude (∼1 ns < τes < 45 μs). Terpyridyl pyrrolidinyl substituents can be utilized to destabilize terpyridyl ligand π* energy levels and diminish the E1/2 (M3+/2+) value of the bis(terpyridyl)metal(II) center: such perturbations determine the relative energies of the PZn n-derived 1π−π* and bis(terpyridyl)metal(II) charge-transfer states and establish whether the T1-state wave functions of MPZn n and Pyr m MPZn n species manifest the extensive electronic delocalization and charge-separated (CS) features characteristic of long-lived triplet states that absorb strongly in the NIR.

This publication has 52 references indexed in Scilit: