The objective of this project was to understand how the structure of helical polymers affect the optical rotation of a polymer. Python code was used to create a 13 ring furan oligomer. The shape of this oligomer was a ring. To induce the structure into a helical shape, the dihedral angles of the oligomer were set to 10, 20, 30, 40, 50, 60, and 70 degrees. The different angles correlate to different pitch helices. The dihedral angles were constrained using xTB quantum chemistry tool. Once the structures were created, ORCA, another quantum chemistry package, was used to calculate the electrical dipole moment, magnetic dipole moment, and optical rotation. Based on an analogy to a solenoid, the expected result was to see a decrease in magnetic transition moment as the pitch of the helices increased. This trend was observed in the data. We also expected to see an increase in the electrical transition moment as the pitch increased; however, this trend was not observed. Another unexpected result is that the angle between the magnetic and electric dipole vectors are nearly orthogonal to each other Since the optical rotation is the dot product of the magnetic and electric transition dipole moment, the optical rotation is highly sensitive to the angle between the magnetic and electric transition moment. This means that the angle is playing a bigger role than initially thought. Another result was that, for dihedral angles greater than 40 degrees, the shape of the oligomer looked more like a hairpin than a helix. We are now working on alternative approaches to constrain conjugated polymers into helical shapes.
