Optical amplification in DNA-surfactant complexes incorporating hemicyanine dyes with long and short alkyl chains

摘要

Hemicyanine dyes are promising materials for solid-state tunable dye lasers because of their high activity for light amplification and superior durability under optical pumping when doped in DNA-surfactant complexes. A hemicyanine with a long alkyl chain, 4-[4-(dimethylamino)stylyl]-1-dococylpyridium bromide (DMASDPB or Hemi22) has been incorporated in the complex films prepared with various methods, demonstrating amplified spontaneous emission (ASE), laser oscillation and its wavelength tuning. While these achievements have seemed to confirm the importance of intercalation or groove-binding of the dyes to DNA strand, our recent studies for the hemicyanine and other dyes suggested that the influence from surfactant molecules was more essential than that from DNA structure. Considering that dye-DNA interaction mode may strongly depend on the size and structure of the dye molecules, another hemicyanine, 4-[4-(dimethylamino)stylyl]-l-methylpyridium iodide (DMASMPI or Hemil) with methyl substituent instead of C22 of Hemi22, was employed as dopant in the complex for comparison. DMASMPI-doped-complex films prepared by the same method also showed ASE under optical pumping with a threshold value nearly identical to that for DMASDPB, suggesting common interaction feature. On the other hand, the dye had high solubility in water and gave fluorescence enhancement when dissolved in aqueous solution with DNA, indicating direct interaction between the dye and DNA double strand.