Design and synthesis of sulfobetainic diketopyrrolopyrrole (DPP) laser dyes

We have devised new diketopyrrolopyrrole dyes soluble in polar solvents. The colors of the dyes have been changed by substituting the 3,6-phenyl residues for thiophene groups. The solubility in polar solvents has been improved by alkylation of a dimethylaminopropyne fragment with a 1,3-sultone giving rise to sulfobetaine moieties. These dyes exhibit strong and broad absorption in the visible range (488 nm for the phenyl-DPP and 578 nm for the thiophene-DPP) and intense fluorescence at, respectively, 554 nm (ΦF 0.36) and 609 nm (ΦF 0.19). The phenyl-DPP dye exhibits a maximum broad band lasing efficiency of 14.6% and a maximum narrow band lasing efficiency of 9.5% with a wide tunable range (554 nm to 616 nm) on excitation with a second harmonic of a Q-switched Nd:YAG (532 nm) laser in MeOH/H2O. The lasing efficiency remains unaffected for hours. The thiophene-DPP dye does not show any lasing action.