Synthesis and Properties of Perylene-Bridge-Anchor Chromophoric Compounds

Abstract

The quest to control chromophore/semiconductor properties to enable new technologies in energy and information science requires detailed understanding of charge carrier dynamics at the atomistic level, which can often be attained through the use of model systems. Perylene-bridge-anchor compounds are successful models for studying fundamental charge transfer processes on TiO 2 , which remains among the most commonly investigated and technologically important interfaces, mostly because of perylene's advantageous electronic and optical properties. Nonetheless, the ability to fully exploit synthetically the substitution pattern of perylene with linker (= bridge-anchor) units remains little explored. Here we developed 2,5-di-tertbutylperylene (DtBuPe)-bridge-anchor compounds with t-Bu group substituents to prevent π-stacking and one or two linker units in both the peri and ortho positions, by employing a combination of Friedel−Crafts alkylations, bromination, iridium-catalyzed borylation, and palladium-catalyzed cross-coupling reactions. Photophysical characterization and computational analysis by density functional theory (DFT) and time-dependent DFT (TD-DFT) were carried out on four DtBuPe acrylic acid derivatives with a single or a double linker in peri (12b), ortho (15b), peri,peri (18b), and ortho,ortho (21b). The energies of the unoccupied orbitals {LUMO, LUMO + 1, LUMO + 2} are strongly affected by the presence of a π-conjugated linker, resulting in a stabilization of these states and a red shift of their absorption and emission spectra, as well as the loss of vibronic structure in the spectrum of the peri,peri compound, consistent with the strong bonding character of this substitution pattern.

Conformational and Binding Effects on Interfacial Electron Transfer from Dual-Linker Sensitizers

“…To accelerate the calculations, simplified model compounds, in which the bulky tert -butyl groups (DtBuPe) were substituted by methyl groups (DiMePe), were used as surrogate compounds. It was verified, both in static and dynamics calculations, that this substitution did not induce significant changes to the results . The DFT results were then used as a reference to parameterize a semiempirical extended Hückel (eH) model upon which the coupled CT/MM simulations were carried out.…”

“…The structure of the four sensitizers that were investigated, ( E )-3-(8,11-di- tert -butylperylen-2-yl)­acrylic acid, (2 E ,2′ E )-3,3′-(8,11-di- tert -butylperylene-2,5-diyl)­diacrylic acid, ( E )-3-(8,11-di- tert -butylperylen-3-yl)­acrylic acid, and (2 E ,2′ E )-3,3′-(8,11-di- tert -butylperylene-3,4-diyl)­diacrylic acid, are shown in Figure a; they will be termed ortho, bis-ortho, peri, and bis-peri, respectively. The synthesis, the optical and electronic properties, and the static QM calculations of the electronic structure of the unbound sensitizer have been reported elsewhere . Briefly, a significant red shift of 30 and 50 nm in the ground-state absorption was observed for the peri and bis-peri sensitizers, respectively.…”

“…(a) Molecular structure and abbreviations of the novel sensitizers investigated here . (b) UV–vis difference spectra of ortho, bis-ortho, peri, and bis-peri bound to colloidal TiO 2 .…”

“…The substitution pattern has a strong influence on the delocalization of the perylene frontier orbitals over the bridge groups. Since it affects the electronic coupling, it was expected that the difference in delocalization would be reflected in the IET dynamics . While the sensitizers have two identical linkers, the binding mode is such that only one linker binds covalently via the carboxylic acid anchor group on the {101} surface of anatase, while the other linker is only weakly bound with the surface via hydrogen bond or electrostatic interactions.…”

“…This approach will allow us to separate functionalities in multilinker sensitizers and explore strategies that result in additional functionalities for molecular sensitizers. It should be noted that it is not limited to structurally identical linkers, and we have already developed strategies toward perylenes with different linkers …”