The systematic extension of the pi-conjugated system of strongly blue-luminescent dithieno[3,2-b:2',3'-d]phospholes has been investigated with the goal of obtaining different emission colors. Functionalization of the 2- and 6-position of the dithienophosphole scaffold with halogen substituents provided functional building blocks for subsequent cross-coupling experiments with various homo- and heteroaryls to selectively decrease the band gap of the materials. By this strategy materials with different emission colors ranging from green via yellow to orange could be obtained. This feature supports their suitability for organic light-emitting diodes with respect to an application in full-color flat-panel displays. The experimental results were nicely supported by theoretical DFT calculations providing a deeper understanding of the electronic structure in the extended materials, and also allowing for the design of future materials based on a dithienophosphole core. Furthermore, the phosphorus center in the extended molecular materials can efficiently be fine-tuned in subsequent simple chemical functionalizations. This allows for a tailoring of the optoelectronic properties of the extended dithienophospholes to suit the requirements of potential applications.
To explore their suitability for applications in molecular optoelectronics and as sensory materials, novel dithieno[3,2-b:2',3'-d]phospholes have been synthesized and their reactivity and properties investigated. An efficient two-step synthesis allowed for a modular assembly of differently functionalized compounds. The dithieno[3,2-b:2',3'-d]phosphole system exhibits extraordinary optoelectronic properties with respect to wavelength, intensity, and tunability. Owing to the nucleophilic nature of the central phosphorus atom, its significant electronic influence on the conjugated pi system can be altered selectively by chemically facile modifications such as oxidation or complexation with Lewis acids or transition metals. All the dithienophosphole species presented show very strong blue photoluminescence with excellent quantum yield efficiencies supporting their potential utility as blue-light emitting components in organic light emitting diodes (OLEDs). Furthermore, depending on the electronic nature of the phosphorus center, the materials exhibit distinctive optoelectronic properties suggesting that the dithieno[3,2-b:2',3'-d]phosphole system may be useful as sensory material. Theoretical calculations, including time-dependent DFT methods, revealed the excellent predictability of the structures and optoelectronic properties of the functionalized dithienophospholes allowing the design of future dithieno[3,2-b:2',3'-d]phosphole-based materials to be "stream-lined". By using tin-functionalized dithienophosphole monomers, a strategy, which involves Stille coupling, towards extended pi-conjugated materials with significantly redshifted optoelectronic properties is also presented.
A series of dithieno[3,2-b:2',3'-d]phosphole-based transition metal complexes, including Au, Fe, Pt, Rh and W as central metals have been synthesised and characterised. Structural investigations by X-ray single crystal crystallography supported the high degree of pi-conjugation in the dithienophosphole ligands. This essential requirement for potential applications in molecular electronics and optoelectronics provides small band gaps for the materials. Investigations toward the optoelectronic properties of the respective complexes by fluorescence spectroscopy indicated that systematic alterations of the electronic structure are connected to different variables such as transition metal employed, functionalisation of the dithienophosphole ligands as well as complex geometries. The investigated Pt-based complexes exhibit only poor photoluminescence whereas Rh-, W- and Fe-based species with silyl functionalised dithienophosphole ligands show appreciable photophysical properties. The Au complexes investigated exhibit strong photoluminescence properties with very intriguing features in terms of excitation and emission wavelengths, intensity as well as selectivity.
[structure: see text]. The newly developed functionalization of an unsubstituted dithieno[3,2-b:2',3'-d]phosphole at the 5,5'-positions gives access to bis(pinacoleboryl) species that can be utilized as sensory materials for fluoride ions. The fluoride-triggered response of the air- and moisture-stable boryl-functionalized dithienophosphole oxide manifests itself in the generation of a new fluorescence emission that can be detected at very low analyte concentrations (ppm) or even with the naked eye upon irradiation with UV light (366 nm).
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