Solvation effects on the ground and excited states of p-n diblock-conjugated polymers: Theoretical insights

A semiempirical study was carried out to give theoretical insights of the solvation effects on the absorption and emission wavelength of oxadiazole-containing p-n diblock-conjugated polymers at both ground and excited states on the basis of experimental results. The Conductor-like Screening Model was used to calculate the absorption and emission wavelengths of the carefully designed model molecules in solvents with different dielectric constants (approximately ε = 1-35) from the optimized ground states and the lowest excited states by coupling AM1 formalism to the new configuration interaction scheme. The calculated results agree well with the experimental observations of the corresponding polymers. The geometrical modifications, charge changes upon photoexcitation, frontier orbital distributions, and dipoles of the two model molecules were investigated and discussed to explain the different solvation behavior of the corresponding diblock copolymers. The different charge-transfer behavior was suggested to be the major factor that causes the varied solvation effects of the p-n diblock molecular systems at excited states upon photoluminescence. These findings may provide important insights at the molecular level for selectively tuning the solvatochromic properties of p-n diblock-conjugated polymers for practical applications.