# Amplification of Chirality in Photopatterned 3D Nanostructures of Chiral/Achiral Mixtures
## 3 Results and Discussion  
Understanding the physiochemical interactions between nanocrystals and supramolecular systems that can amplify chirality is complicated, and CD intensity has been used to understand chirality in molecular systems. When chiral molecules absorb circularly polarized light, the CD also increases; therefore, measuring the CD intensity is an effective method for understanding the chirality [42; 43; 44; 45]. To investigate how the enhancement of the optical activity varied based on the solid content of SU-8, PFBT/SU-8 solutions with a solid content of SU-8 from 10% to 50% (mixture ratio of PFBT:SU-8 = 1:40) were prepared and spin-coated on the glass substrates. Figure 3 shows the measured CD intensity of the coated PFBT/SU-8 films, without annealing and with annealing. The black squares stand for the PFBT/SU-8 substrates without annealing and the red circles stand for the PFBT/SU-8-coated substrates with annealing. As mentioned above, the chiroptical characteristics of molecules can be induced by annealing, and as Figure 3 shows, the measured maximum CD intensity of the overall samples clearly shows the enhancement of chirality after annealing. Figure 2: Two-photon lithography setup with a movable stage. After the annealing of the PFBT/SU-8 films, the CD increased 2.16-2.83 times and the maximum increased CD for the solutions with 10%, 20%, 30%, 40% and 50% solid contents were 131 mdeg, 498 mdeg, 635 mdeg, 848 mdeg and 644 mdeg, respectively. By using the two-photon lithography setup, the PFBT/SU-8-coated films were exposed to a femtosecond laser to make an 'L' shape and developed by PGMEA to dissolve the unpolymerized area. After measuring the CD of the developed samples, they were annealed at 150 \({}^{\circ}\)C for 15 min and measured by CD spectroscopy again. In Figure 3, the blue triangles stand for the CD of the patterned samples without annealing and the green inverted triangles stand for the CD of the patterned samples with annealing. After annealing, the CD of all samples increased, with the 30% sample showing the best result. The main explanation for the CD enhancement is a change in the supramolecular ordering, which causes an increased helicity in the mixtures [37]. By annealing the sample, the helical fibrils of the patterned structure became liberated from the mixture and had a larger freedom, which caused the supramolecular conformation of the material. Among the samples, the sample with a solid content of 30% had the most ideal conditions for changing the supramolecular conformation, and consequently, it showed the best CD enhancement after annealing. On the other hand, the maximum CD of the annealed samples with 30%, 40% and 50% solid content were relatively lower than the maximum CD of the PFBT/SU-8 films with the same solid content of SU-8. Compared with pure PFBT film, the CD of the patterned PFBT/SU-8 structures were enhanced by 10-25 times and the solution with a solid content of 30% showed the greatest CD (632 mdeg) among them. Previous studies have described that developed PFBT/SU-8 structures after annealing show exceptionally large, enhanced CD through the formation of chiral aggregates [37]. In this case, the dispersed PFBT in the SU-8 formed nanocomposites, which played a key role in the enhancement of the CD. In addition, by using a UV light, a PFBT/SU-8 structure was fabricated and the patterned structure had a 30 times enhanced CD compared to a pure film without nanocomposites [38]. This study showed that without residual nanocomposites, polymerized PFBT/SU-8 mixtures that go through a development and annealing process still receive an advantage from the formation of chiral aggregation; therefore, the CD can be enhanced. Otherwise, although the structure patterned by two-photon lithography still showed an enhanced CD, the maximum CD intensity was lower than that of the structures fabricated by UV lithography. Figure 4 shows the schematic of the two-photon lithography and UV lithography.