Objectives: Challenges addressed by this project:
• The development of methods of bioimaging needs new optical phenomena which out-perform conventional approaches.
• Two Photon Circular Dichroism (TPCD) is an important photophysics experiment that is held back by the lack of suitable high-performance molecules.
• Donor-(chiral-π)-Acceptor NLOphores based on heterohelicenes have been predicted to offer ultra-high-perfomance properties for TPCD but are hard to make enantiomerically pure.

Approach to be adopted: A new class of helicenes has been devised that will be easy to make, is intrinsically polarised in the required "Donor-(chiral-π)-Acceptor" form, and has easily variable substitution patterns for optimisation. This novel class of 5,5,6,5,5 tetra-fused hexaazahelicenes will be prepared in Norwich and evaluated in collaboration with the photophysics research group of Prof Thierry Verbiest in Leuven.

Research work: 
This is a synthetic organic chemistry research project. Applicants with skills and interests in enantioselective synthesis are encouraged to apply. Organic substrates for intramolecular double click reactions will be prepared and evaluated with copper catalysts and chiral ligands of the tren and NHC types, often evaluating with copper, ligands which are readily available but typically employed in asymmetric synthesis with other metals (e.g. palladium and gold). This project will establish the first ever application of the copper click reaction in enantioselective synthesis.

The research project is hypothesis-driven: Research Hypothesis 1. The advantages of helicenes for TPCD (putting "chiral-π into "Donor-(π)-Acceptor" NLOphores): To succeed with TPCD, materials are needed where the left- and right-hand forms are very different ("highly anisotropic"). With a large difference, there is the best prospect of characterising the consequences of the difference. The choice of helicenes for this project is crucial since this not only ensures highly anisotropic structures, but also introduces intrinsic chirality into the π system itself. The proposal is that the because of its "chiral π-system", the helicene class of structures is especially suited for the purpose.

Research Hypothesis 2. The advantage of the "double-dipole half-turn" design: Conventionally, donor and acceptor groups are placed at the ends of the systems of D-π-A NLOphores. With C2 symmetric helicene-based (D)-(chiral-π)-(A) structures, an earlier theoretical study from our COST D14 collaboration has suggested that functionalisation of the central ring of the helix is an important strategy. The proposal is that two shorter (D)-(chiral-π)-(A) structures each occupying a half turn of the helix will be more powerful than a single longer (D)-(chiral-π)-(A) spanning a full turn.

The PhD project will test these two hypotheses with a novel class of 5,5,6,5,5 tetra-fused hexaazahelicenes, prepared by a new methodology based on click chemistry. Despite the fact that both the target molecule class and asymmetric induction process are novel, the prospects of rapidly gaining results in this project are good because of the choice of the widely applied click chemistry approach. Click reactions are easy reactions with a strong driving force, but because of the use of chiral ligands they will be applied in a novel way in this research project.

Bossi, A.; Licandro, E.; Maiorana, S.; Rigamonti, C.; Righetto, S.; Stephenson, G. R.; Spassova, M.; Botek, E.; Champagne, B. Theoretical and Experimental Investigation of Electric Field Induced Second Harmonic Generation in Tetrathia[7]helicenes. J. Phys. Chem. C (2008), 112, 7900-7907.

Monteforte, M,; Cauteruccio, S.; Maiorana, S.; Benincori, T.; Forni, A.; Raimondi, L.; Graiff, C.; Tiripicchio, A.; Stephenson, G. R.; Licandro, E. Thiaheterohelicene phosphanes as helical shaped chiral ligands for catalysis. Eur. J. Org. Chem. (2011), 5649-5658.

Savoini, M.; Wu, X.; Celebrano, M.; Ziegler, J.; Biagioni, P.; Meskers, S. C. J.; Duo, L.; Hecht, B.; Finazzi, M. Circular Dichroism Probed by Two-Photon Fluorescence Microscopy in Enantiopure Chiral Polyfluorene Thin Films. J. Am. Chem. Soc. (2012) 134, 5832−5835; (recent example of imaging applications)