Density functional theory study of solid-state structure and optoelectronic properties of fluorene-based conjugated polymers

Eslamibidgoli, Mohammad Javad (2012) Density functional theory study of solid-state structure and optoelectronic properties of fluorene-based conjugated polymers. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (26MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Using the dispersion corrected density functional theory (DFT-D/B97D) approach, we have performed molecular and solid-state calculations to study the influence of intra- and inter-molecular interactions on the bulk structure and the electronic and optical properties of fluorene-based conjugated polymers. In particular, we investigate the role of side-chain length on the molecular parking and optical properties of poly (9.9-di-n-alkylfluorene-alt-benzothiadiazole) or FnBT's where n is the number of CH₂ units in the alkyl side-chains. The results indicate that for the FnBT with longer side-chains, due to the significant inter-molecular interactions between the side-chains, the packing of these polymers forms a lamellar structure. On the other hand, for the FnBT with shorter side-chains, the cylindrical phase is more favorable and the corresponding crystals are almost hexagonal. These different packing structures can be attributed to the microphase separations between the flexible side-chains and the rigid backbones and are in agreement with previous investigations for other hairy-rod polymers [1, 2]. In addition, as a result of the efficient inter-chain interactions for the lamellar structures, the dihedral angle between the F and BT units is reduced by about 30ﾟ providing a more planar backbone which in turn leads to a decrease of about 0.2eV and 0.3 eV, in the band gap of the lamellar structure relative to its value for the gas and cylindrical phases respectively. Time-dependent DFT is also used to study the excited states of the monomer of FnBT with various lengths of side chains.

Actions (login required)

View Item