Structural and electronic properties of poly(fluorene-pyrrole) copolymer: Time dependent density functional theory investigation

The structural and electronic properties of fluorene-pyrrole copolymer (FPyr)_n n=1-4 were theoretically investigated. Geometry optimizations of this oligomer were calculated at the B3LYP/SVP and TD-B3LYP/SVP for the ground state and the first lowest excited state, respectively. The obtained results found that (FPyr)_n is non-planar structure in its ground state whereas completely planarity in the S₁ state. The lowest excitation energy of this oligomer carried out at the TD-B3LYP/SVP and TDB3LYP/ SVP+ are 2.25 and 2.23 eV, respectively. The S₁ ¿ S0 electronic transition is characterized as the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) transition which dominated in terms of oscillator strength. The fluorescence energy of (FPyr)_n calculated by TD-B3LYP/ SVP and TD-B3LYP/SVP+ are 1.87 and 1.85 eV, respectively and the predicted radiative lifetimes are 0.86 and 0.89 ns, respective. These structural and electronic properties can be useful in designing of novel conducting polymer materials.