Multiscale investigation of polyfluorene chain-length dependence on nanotube selective wrapping

E.J. Figueiredo de Carvalho, W. Gomulya, L. Zheng, A. Hermann, M. Cristina dos Santos, S.-J. Marrink, M. Antonietta Loi
University of Groningen, NL

Keywords: carbon nanotube, polyfluorene, PFO, photoluminescence, multiscale, molecular dynamics, coarse-grained, ZINDO

Summary:

In this work we investigate selectivity dependence on PFO chain length and chain length distribution. PFO samples with broader molecular weight (MW) distributions exhibit stronger selectivity towards (8, 6) nanotubes than those that are more uniform in chain length. Coarse-grained (CG) molecular dynamics, as implemented in the MARTINI force field for the GROMACS package, is used to sample PFO conformations around nanotubes in toluene solutions. Different chain lengths and molecular weight distributions, from 9 × 103 a.m.u to 250 × 104 a.m.u, are considered in the simulations in order to mimic those observed in our experiments. Samples from the CG simulations serve as initial states for atomistic molecular dynamics. At this stage, the force field is parametrized as to reproduce the excited state conformation of the polymer. The obtained PFO conformations are further used to calculate the emission spectra by the ZINDO/S-CI technique as implemented in the Gaussian09 package. The simulated photoluminescence (PL) spectra are then compared to experimental PL spectra of PFO in nanotube suspensions. Differences observed in polymer PL in solution and SWNT suspensions allow the determination of the polymer chain conformation around the nanotubes and consequently the selectivity mechanism can be explained.