LAUSR

Abstract A new centrosymmetric D-π-D molecule, TTF-CH=CH-CH=CH-CH=CH-TTF ( 1 , TTF: tetrathiafulvalene) was synthesized and its absorption and fluorescence solvatochromic behaviors were compared with those of Me 2 NPh-CH=CH-CH=CH-CH=CH-PhNMe 2 ( 2 ). The lowest-energy absorption band of 1 shifts to blue as the solvent polarity increases. The wavenumber of the maximum peak correlates well with the Onsager polarity function f(e)−f( n 2 )=(e−1)/(2e+1)−( n 2 −1)/(2 n 2 +1). Considering the non-dipolar nature of 1 due to its highly symmetric structure, we conclude that the observed negative solvatochromism is related to the quadrupole (solute)-dipole (solvent) electrostatic interaction. For 2 , we see the trend of positive solvatochromic shift, although the absorption maximum correlates only very weakly with f( n 2 ). The result suggests that the solvatochromism is mainly related to the dispersion-like interaction. The different absorption solvatochromic behaviors of 1 and 2 can be attributed to the strong quadrupole character of 1 relative to that of 2 , resulting from very strong donating ability of TTF. As for the fluorescence, positive solvatochromism is similarly observed for 1 and 2 . The emission maxima correlate fairly well with f(e)−f( n 2 ). Most probably, molecules 1 and 2 experience the excited-state symmetry breaking with possible geometrical relaxation from non-dipolar Frank-Condon states to dipolar, charge transfer emitting states at least in polar solvents.