EDA study of pi-conjugation in tunable Bis(gem-diethynylethene) fluorophores

The strength of pi-conjugation in a family of bis(gem-diethynylethene) fluorophores is estimated within the density functional theory framework using the energy decomposition analysis (EDA) method. The observed very good linear correlations between the calculated pi-conjugation and the experimental values for the UV absorption and fluorescence emission for this series of compounds suggest that the values given by the EDA are useful for the interpretation and prediction of photochemical properties of the molecules. The calculated data predict that adequate modifications in the core moiety of the molecule such as pi-donor substituents in the aromatic ring or in the periphery of the bis-enedyine unit like pi-acceptor groups placed in the para position of the aryl substituent increase the total pi-conjugation in the systems and thus provoke significant changes in both the absorption and emission spectra leading to large Stokes shifts. The effect of such substituents is quantitatively predicted by the EDA data.