A pattern for increasing the first hyperpolarizability of a push-pull polyene dye as indicated from DFT calculations

Density functional theory (DFT) calculations were performed on a polyene dye scaffold, keeping the end groups and bridge length the same but varying the pattern of electron-donating (D) and electron-withdrawing (W) substituents along the polyene bridge. The basic pattern that increased the first hyperpolarizability was to place W substituents on even-numbered (e) methine carbons, and D substituents on odd-numbered (o) methines (called the {eWoD} pattern). The numbering scheme used herein for the dye scaffold has the #1 methine at the W-terminus of the dye. The {eWoD} pattern polarizes the 7 bonds along the polyene in the opposite direction that the termini of the dye polarize the dye. By placing cyano and fluorine groups in the 1 eWoD) pattern along the polyene, a sixfold higher first hyperpolarizability was predicted compared to placing them in the opposite substitution pattern ({JoWeD}). A superimposed but weaker gradient pattern was also observed.