WP1: CHIRAL MATTER
The synthesis of Boc-protected racemic amino helicene has successfully been performed. The synthesis was more problematic than described previosly, as a regioisomer was formed in the first synthetic step.A total of 2.6 g racemic Boc-protected amino helicene was synthesized. It was decided to keep the material in this stage as it is believed that the chemical stability of the unprotected amino helicene may not be suitable for long-term storage. Two portions of 150 mg racemic Boc-amino helicene were separated into its enantiomers via preparative SFC. The pure enantiomers and some racemates were shipped to the AMOLF institute for further analyses.
We have also been able to fabricate chiral plasmonic nanocubes showing chiral response - characterized in CD measurements - in the wavelength range between 600 and 800 nm. Such nanocubes are very promising for performing experiments and test on silicon photonic chips.
Using DFT, we have been able to compute the chiral polarizability of some molecules, particularly helicene. We plan to continue working with this method that will enable to link the chemistry (WP1) with the optics (WP2).
WP2: CHIRAL OPTICS
The description of optical forces in the most general case is quite confusing in the literature: different works use different definitions, assumptions, notations, etc. Calculating optical forces reliably was, therefore, a challenge. One of the first aims of CHIRALFORCE was to provide a reliable, clear, and correct expression for optical forces, with all the definitions clearly stated, and all equations carefully derived to ensure consistency with the definitions. A complete and exact description of all optical forces on a dipolar (small) particle was therefore derived and described from first principles, establishing the definitions to be used by all partners in CHIRALFORCE. The results are contrasted with existing literature, highlighting the differences (in terms of definitions, unit systems, prefactors, missing terms, etc.) with each prior work. Our work is, to our knowledge, the only one including all terms of the dipolar force while at the same time providing two alternative (but equivalent) calculation methods: the field-centric approach, and the particle-centric approach.
We applied our equations to two optical systems: cylindrical optical fibers and silicon nitride photonic integrated waveguides. In the case of the waveguides, our study considered force strength and time needed for separating chiral nanoparticles, mainly via quasi-TE guided modes at short wavelengths (405 nm) and the 90°-phase-shifted combination of 14 quasi-TE and quasi-TM modes at longer wavelengths (1310 nm). Particle tracking simulations show successful enantiomer separation within two seconds. These results suggest the feasibility of enantiomeric separation of nanoparticles displaying sufficient chirality using simple silicon photonic integrated circuits, with wavelength selection based on the nanoparticle size.
We also have prepared a full optical set-up to measure the chiral scattering properties of chiral nanoparticles, driven by evanescent fields with superchiral properties.
WP3:Demonstrator of enantioselective separation
A characterization set-up for testing photonic integrated waveguides (wavelengths 1310, 780 and 633 nm) is running. First waveguides and circuits on SiN have been fabricated ad tested. Pressure drop calculations have been performed for various dimensions of microchannels to be integrated on waveguides. Different designs have been made for the waveguide and microfluidics integration (test structures). A process flow has been designed for the fabrication of the test structures using a sacrificial layer approach. Assembly of the first chirality detection platform using JASCO-1500 CD spectrophotometer and modification of its optical path for potential in-line measurement (Detection system v0.1). Testing the chirality measurement capability of this v0.1 with test chemical CSA has been performed.
