Highly fluorescent oligomers with donor and acceptor groups: DFT calculations and experiments

We investigate π-conjugated oligomers with donor and acceptor groups using the DFT method and compare the theoretical excited states with the observed photophysical properties. The oligophenylene ethynylenes substituted by methoxy and cyano groups in a block manner exhibit high fluorescence at longer wavelength region (Y. Yamaguchi, et al., J. Phys. Chem. A 112 (2008) 5074 [5]). We demonstrate that the S1 state of these highly fluorescent molecules has the character of intramolecular charge transfer and discuss the relevance of this character to the photophysical properties like bathochromic effects. We also examine substitution effects on the ring torsion around the triple bond.