| People involved: | Ivan Scheblykin |
| Former members: | Oleg Mirzov |
This project is related to the following Fields, Subjects and Techniques:
| Fields: | Computational Chemistry |
| Subjects: | Organic Semiconductors |
| Techniques: | Single molecule spectroscopy |
The aim of this project is to use simple and computationally inexpensive models to simulate conformations, excitation energy migration and spectroscopic and polarisation properties of long (~1000 monomers units) conjugated polymer chains. The project therefore consists of two parts: chain conformation simulations (done using the Monte Carlo bond fluctuation method) and energy transfer and spectroscopic properties simulations (done using the concept of spectroscopic units, elements of exciton theory and the line-dipole modification of the Förster theory).
The simulation approach to this problem was based on the bond fluctuation method with a set of modifications. The basic algorithm models a polymer chain as a sequence of bound beads with variable bond length. The beads may only be situated in the knots of a square lattice. Every bead represents a Kuhn's segment of the chain. The modifications were as follows. Firstly, the length of the bond was geometrically allowed to change from 3 to 7 grid units, but a harmonic potential was imposed on the shift of the bond length from the equilibrium value of 5 units. Secondly, stiffness potential (which allowed to consider every bead as a monomer unit, not a Kuhn's segment) and interaction between non-neighbouring beads (via Lennard-Jones potential) were introduced. Finally, instead of first generating a random chain without the potentials and then switching the potentials on and "shaking" the chain with Monte Carlo steps, it was "synthesized" during the simulation with all the potentials switched on from the very beginning, thus providing some more realism. An example of a result of such calculation is shown below (click the picture to open an animated gif file):
The above example was done with somewhat exaggerated attraction, so a part of the chain crystallized. This can be very clearly seen from the following animation (click the picture to open an animated gif file, 3.1 MB):
By changing the stiffness of the chain and tuning the Lennard-Jones potential parameters (which corresponds to changing the solvent) one can obtain more or less collapsed conformations.
Back to topAfter the conformation is obtained, the next step is to "chop" the chain into spectroscopic units, assign their spectra, and calculate the energy transfer between them. Having that done, one can calculate any spectroscopic and polarisation property of the chain. Another possibility is to introduce an excitation quencher and see how it affects the results:
