Table of Contents:
The primary focus of this thesis, which was conducted within the SFB 1083, was the synthesis and characterization of perylene diimides (PDI) and perylene-based hetero-polyaromatic hydrocarbons for optoelectronic and photophysical investigations at internal interfaces.
The photoinduced electron transfer (PET) in perylene dihydrazides was invsetigated. PET leads to a fluorescence quenching since the radiative decay from the LUMO to the HOMO–1 is blocked, and results in fluorescence quantum yields below 1% for PDHs. To gain a better understanding of the PET, donor-acceptor PDIs with varying alkyl spacers were prepared. While the absorption and emission spectra of all PDHs and PDIs were virtually identical, ΦPL increases with growing donor-acceptor distances. Protonation and methylation of the amino donor lead a fluorescence recovery. Time-resolved fluorescence spectroscopy reveals an unexpected, non-single-exponential decay of the emissive states.
Following the investigation of PET in PDHs, new AB-type perylenes were obtained via the modification of the carbonyl moieties. Anchor groups were introduced to create model systems for the investigation on internal interfaces and to control the optical and electronic properties. The reduction of perylene monoanhydride diesters with standard reduction agents led to the formation of asymmetrical pyranoperylenes. An electronically decoupled acyanoacrylate anchor was introduced and perylene hydropyrano anhydride was developed as a building block for future push-pull systems.
The reduction of the carbonyl moieties led to the main topic of this work. A new access to fourfold alpha-functionalized 2,9-diazadibenzoperylenes (DDP) und dibenzoperylenes (DBP) was developed using reductive aromatization, which led to a new class of heteropolyaromatic dyes. The optical and electrochemical properties were modified by chemical functionalization and investigated using spectroscopic and electrochemical measurements.
The pigment PTCDI, which is commercially available in large amounts, was used as the starting material in the reduction of the imide moieties with sodium or potassium graphite. In a second step, silylation led to the formation of soluble DDP tetrasilylether DDP 1. Following the optimization of the reaction conditions for DDP 1, a synthesis for 1,3,8,10-tetratriflate DDP was developed, which served as a new key compound for alpha-functionalized DDPs. The fourfold triflation was achieved via two synthetic approaches. One approach required in a first step the lithiation of DDP 1 with n-BuLi and in a second step the reaction of the resulting lithium salt with trifluoromethanesulfonic anhydride. In a second method, DDP 8 was obtained via direct triflation of DDP 1 in the presence of catalytic amounts of DMAP.
The same method of reduction and silylation of PTCDI was used for the synthesis of dibenzoperylenes, a second class of polyaromatic dyes. The thus obtained 2,9-methyl-1,3,8,10-silylether dibenzoperylene was converted into the corresponding tetratriflate, yielding a starting material for functionalization of dibenzoperylenes. The developed method enables the introduction of alkyl and aryl substituents in the 2- and 9-position und therefore provides an additional possibility to tune the properties.
DDP 1 can be considered a protected leuco form of a reduced and soluble vat dye of PTCDI. It re-oxidizes under ambient atmosphere to form PTCDI. Therefore, a selective hydrolysis and oxidation of DDP silylethers provides a new method for the solution-processed coating of transparent PTCDI films on e.g. glass. The tetratriflates are also air-sensitive, and in case of DBP 2 light-sensitive, compounds. Two scaffolds are available for further functionalization: a pure polyaromatic hydrocarbon and a nitrogen-containing heterocyclic aromatic compound.
Starting from DDP 8, tetraaryl, tetraalkynyl and tetraamino DDPs were obtained. A variety of electron-rich and electron-poor aryl substituents was introduced onto the DDP scaffold and characterized using x-ray crystallography. The influence of the aryl substituents on the optical and electronic properties was systematically investigated. Two electron-rich heteroaromatic compounds were obtained: tetraalkyne DDP 24 was synthesized via a fourfold SONOGASHIRA cross-coupling reaction and tetraamino DDP 30 via nucleophilic substitution in DMSO.
Using cyclovoltammetric and differential puls voltammetric measurements, lower oxidation and reduction potentials are observed for DDPs than for perylene diimides, making DDPs more electron rich. The introduction of electron-poor aryl substituents leads to a systematic increase of the oxidation potential thus enabling a fine-tuning of the electrochemical properties.
The introduction of phosphinite moieties led to three PONOP pincer ligands for the complexation of up to two metal centers. One ligand was crystallographically characterized and employed in the synthesis of group VI and late transition metal complexes.
The manifold functionalizations enable the tuning of the optical and electronic properties via introduction of electron-poor and electron-rich substituents in the 1, 3, 8 and 10 positions. Depending on the substituents, a spectrum of fluorescent 2,9-diazadibenzoperylenes with absorption maxima ranging from 450 nm to 550 nm and emission maxima from 474 nm to 643 nm is accessible. Electron-rich substituents like piperidino and 2-thienyl lead to a redshift of the absorption and emission maxima of over 100 nm relative to tetratriflate and tetraphosphate DDPs. The frontier molecular orbital energies were calculated using optical and electrochemical measurements.
The reductive aromatization and functionalization of PTCDI, the second most important class of dyes and pigments, opens new perspectives for the preparation of new organic semiconducting materials with tunable photophysical properties.