John C. Forgie

Well‐Defined and Monodisperse Linear and Star‐Shaped Quaterfluorene‐DPP Molecules: the Significance of Conjugation and Dimensionality

The synthesis of three new 1,4-diketo-3,6-diphenyl-pyrrolo[3,4-c]pyrrole (DPP) macromolecules appended with two or four quaterfluorene arms is reported. The compounds absorb mainly through the oligofluorene units and emit through the DPP core. Optical gain has been observed for Linear-c, a two-armed structure in which the quaterfluorene units are conjugated through the core unit.

Electrochemical Polymerisation of N-Arylated and N-Alkylated EDOT-Substituted Pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) Derivatives: Influence of Substitution Pattern on Optical and Electronic Properties

New pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) derivatives carrying 3,4-ethylenedioxy-thiophenylphenyl (EDOT-phenyl) substituent groups in the 3- and 6-position, or in the 2- and 5-position of the DPP chromophore were synthesised and electrochemically polymerised. The properties of the polymers were investigated using cyclic voltammetry and UV/Vis absorption spectroscopy. It was found that the optical and electronic properties differ greatly between the two polymers. Materials with EDOT-phenyl groups in the 3- and 6-positions represent conjugated polymers with a low oxidation potential and reversible electrochromic properties, whereas the polymer with EDOT-phenyl groups in the 2- and 5-positions is non-conjugated and possesses a high oxidation potential and irreversible redox behaviour.

Controlling the conformational changes in donor-acceptor [4]-dendralenes through intramolecular charge-transfer processes

The synthesis of two [4]-dendralene compounds incorporating thiophene-(p-nitrophenyl) donor–acceptor units is presented. The dendralenes adopt two different conformers in solution and solid state and the transformation between the structures can be controlled by light and heat. The electron-donating components of the dendralenes are represented by bromothienyl (in 13) and ethylenedioxythiophene(EDOT)-thienyl (in 15) end-groups. The most facile transformation involves the isomerisation of donor–acceptor conjugated systems (a conformers) into structures in which only the thiophenes are conjugated (b conformers), and this process is driven by ambient light. The structures of the two conformers of compound 13 are confirmed by single-crystal X-ray diffraction studies and the structural changes in both compounds have been monitored by 1H NMR spectroscopy and absorption studies. The transformations were found to be first-order processes with rate constants of k = 0.0027 s−1 and k = 0.00022 s−1 for 13 and 15, respectively. Density functional theory calculations at the B3LYP/6-31G∗ level give credence to the proposed mechanism for the a→b conversion, which involves photoinduced intramolecular charge transfer (ICT) as the key step. The EDOT derivative (15) can be polymerised by electrochemical oxidation and a combination of cyclic voltammetry and UV/Vis spectroelectrochemical experiments indicate that the a conformer can be trapped and stabilised in the solid state.

Synthesis and characterisation of new diindenodithienothiophene (DITT) based materials

Three new diindenodithienothiophene (DITT) based materials were synthesised and their electrochemical properties investigated. The HOMO–LUMO gaps were observed to be 3.33, 3.48 and 2.81 eV, respectively. Cyclic voltammetry results indicate increased stability for the alkylated derivatives. The dioxide exhibits strong photoluminescence, giving a photoluminescence quantum yield of 0.72 in solution and 0.14 in the solid state. Hole mobility measurements were carried out on the non-alkylated derivative and the corresponding values were ∼10−4 cm2 V−1 s−1.

Electronic, redox and charge transport properties of an unusual hybrid structure: a bis(septithiophene) bridged by a fused tetrathiafulvalene (TTF)

A hybrid tetrathiafulvalene–oligothiophene compound has been synthesised, in which the fulvalene unit is fused on both sides to an end-capped septithiophene oligomer. The compound (1) has been studied by cyclic voltammetry, UV-vis spectroelectrochemistry and X-ray crystallography. The properties of this material are compared to the half-unit (9), which lacks the TTF core and contains only one septithiophene chain. In the case of the larger molecule, there are multiple and complex redox processes leading to the loss of 6–8 electrons per molecule. Charge generation layer time-of-flight measurements give maximum hole mobilities of ca. 1 × 10−5 cm2 V−1 s−1.

The Introduction of Pyrrolotetrathiafulvalene into Conjugated Architectures: Synthesis and Electronic Properties

A series of new conjugated copolymers incorporating the redox-active pyrrolo-TTF unit has been synthesised. The properties of the polymers have been investigated by cyclic voltammetry and electronic absorption spectroscopy, revealing that the pyrrolo-TTF behaves very differently to its thieno-TTF variant. In comparison to thieno analogues, the band gaps of the new polymers are wider than expected due to a decrease in the polarizability of the heteratom (nitrogen vs. sulfur) and steric interactions between repeat units. Whilst the pyrrolo-TTF units are stronger electron donors than thieno-TTFs in related structures, the two redox active elements of the new polymers (TTF and conjugated chain) function independently under oxidative conditions.