Theoretical Investigation on the Electronic and Optical Properties of Poly(fluorenevinylene) Derivatives as Light-Emitting Materials

Abstract

Density functional theory (DFT) and time-dependent DFT (TDDFT) were employed to study ground-state properties, HOMO-LUMO gaps<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msub><mml:mi>Δ</mml:mi><mml:mrow><mml:mtext>H-</mml:mtext><mml:mtext>L</mml:mtext></mml:mrow></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math>, excitation energies<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msub><mml:mi>E</mml:mi><mml:mi>g</mml:mi></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math>, ionization potentials (IPs), and electron affinities (EA) for PFV- alt -PDONV and PFV- alt -PDIH-PPV having different alternating groups. Excited-state properties were investigated using configuration interaction singles (CISs) while fluorescence energies were calculated using TDDFT. The results show that PFV- alt -PDONV exhibits blue-shifted energies for both HOMO-LUMO gaps<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msub><mml:mi>Δ</mml:mi><mml:mrow><mml:mtext>H-</mml:mtext><mml:mtext>L</mml:mtext></mml:mrow></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math>and excitation energies<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msub><mml:mi>E</mml:mi><mml:mi>g</mml:mi></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math>compared with PFV- alt -PDIH-PPV. The predicted IP and EA clearly indicate that PFV- alt -PDIH-PPV has both easier hole creation and electron injection than that of PFV- alt -PDONV. The maximal absorption wavelengths of all polymers are strongly assigned to<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>π</mml:mi><mml:mo>→</mml:mo><mml:msup><mml:mi>π</mml:mi><mml:mo>∗</mml:mo></mml:msup></mml:math>transition. The predicted radiative lifetimes of PFV- alt -PDONV and PFV- alt -PDIH-PPV for B3LYP/6-31G(d) are 0.36 and 0.61 ns, respectively, indicating that PFV- alt -PDIH-PPV should have a better performance for long-time emission than that of PFV- alt -PDONV.