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The design and synthesis of extended conjugated systems
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posted on 14.02.2017by Rivadehi, Shadi
The work contained within this thesis explores the synthetic strategies to several novel conjugated systems derived from porphyrin, NDI and TTF building blocks and their subsequent characterasation. These novel compounds have applicability in studying the factors that govern ET and EnT in interesting redox processes and as sensors. The bulk of research undertaken utilises the easy to prepare porphyrin-dione 44 and TTF 78 as well as tetrabromo NDI 19.
Chapter 1 provides an introduction to the motivation for this research. The Chapter also summarises major directions in the fields of porphyrin, NDI and TTF chemistry and defines the significance and role of their properties as well as relevant applications.
Chapter 2 explores the synthesis of novel porphyrinogens including oxidation of the porphyrin macrocycle. Core to the strategy is the porphyrin-dione 44. From this dione, porphyrin anhydride 57 and related metallo-porphyrins are synthesised and their physical properties explored. Obtaining porphyrin-lactone 58 as a side product during these reactions led us to synthesis novel lactams 62 and 63. Reaction of porphyrin-lactone 58 with hydrazine-hydrate converts the lactone moiety to an N-aminolactam 62. It also chemically reduces the antipodal pyrrolic moiety in the N-aminolactam, producing the chlorin-like N-aminochlorolactam 63 as well. This lactone-to-lactam replacement does not dramatically change the UV-visible spectroscopic properties of the N-aminolactam 62, however N-aminochlorolactam 63 shows intense Q band at 696 nm, which is larger than that of either of porphyrin-lactone 58 or N-amino-porpholactam 62, and is also shifted to the red region.
Chapter 3 investigates the synthesis of novel porphyrin-TTF systems and their metal complexes. A tetrathiafulvalene donor has been annulated to 44 via quinoxaline linkers to form a novel asymmetric dyad 79. Chemical and physical properties are also outlined by utilising different methods such as UV-visible spectroscopy, fluorescence spectroscopy and cyclic voltammetry. These extended π-conjugated molecules absorb light over a wide region of the UV-visible spectrum. Preliminary fluorescence testing of these compounds suggests that electron and/or energy transfer processes take place from the TTF unit as a donor to the porphyrin moiety as an acceptor. Also, cyclic voltametric studies allow the differentiate between the TTF and porphyrin sites with respect to the multiple redox processes occurring within these compounds. X-ray crystallography was used to characterise compound 79, adding to the structural information gained through other characterisation techniques.
Chapter 4 investigates the synthesis of a new naphthalene diimide 104, in which a TTF donor has been attached to the naphthalene diimide core via a rigid bridge. The electronic properties of 104 are studied in detail. A strong electronic absorption profile extends far into the visible spectral region, which originates from its inherent electronic donor-acceptor nature. Also, the presence of a strong absorption at 1270 nm upon chemical oxidation, confirms significant π-π interactions in the compound due to aggregation.
The work presented in Chapter 5 focused on synthesising of a novel 2,3-dipyrrol-2’-yl-TTF-quinoxaline 123, which is highly selective and sensitive for F- with detection possible by both colorimetric and fluorometric analyses. The target compound 123 was obtained via the direct condensation reaction of 78 with the 2,3-dipyrrol-2’-yl ethanedione 121 in good yield, and then characterized by various methods including X-ray crystallography. The UV-visible spectrum of 123 in DCM shows three strong absorption bands, which change after the addition of fluoride ion. Compound 123 also shows an emission intensity enhancement with slight red shift upon addition of F-, while no significant changes in the spectra of 123 was observed upon addition of AcO-, H2PO4-, Cl-, Br- and HSO4- in the same solvent.
Chapter 6 reflects on the work undertaken in Chapters 2-5 and comments on future directions. It also describes some ancillary works to the main themes of this thesis. Synthesis of the NDI-TTF annulated compounds 126 and 127 under mild conditions are detailed, as well as dimer 128, which might have interesting photophysical properties. A new trimer 130 was also synthesised.