The Nature Of Excited-State Absorption In Polymethine And Squarylium Molecules
Excited state absorption; Femtosecond; Nonlinear optics; Nonlinear spectroscopy; Polymethine dyes; Quantum chemical calculations; White-light continuum
Subpicosecond transient absorption measurements were performed for several polymethine and squarylium dyes in ethanol solution and a polymeric host over the spectral range 400-1500 nm. A variety of nonlinear effects including saturable absorption, reverse saturable absorption, and gain were observed and analyzed. We observe strong excited-state absorption (ESA) in all dyes in the range 450-600 nm. We also report the first prediction and observation of additional ESA bands in the near-infrared range. The predictions were based on quantum chemical calculations and the ESA experiments were performed with femtosecond pump-continuum probe techniques. For polymethine dye 2-[2-[3-[(1,3-dihydro-3,3-dimethyl-1-phenyl-2H-indol-2-yli-dene) ethylidene]-2-phenyl-1-cyclohexen-1-yl]ethenyl]-3,3- dimethyl-1-phenylindolium perchorate, an additional ESA band was detected near 1250 nm, and for squarylium dye 1,3-Bis-[(1,3-dihydro-1-butyl-3,3-dimetyl-2H-benzo[e]indol-2-ylidene)methyl]squa raine, two additional ESA bands were found around 870- and 1380-nm, respectively. To further study the nature of these transitions, the steady-state excitation anisotropy was also studied and compared with predictions. The relationship between ESA spectra of organic dyes and their molecular structure is discussed.
IEEE Journal on Selected Topics in Quantum Electronics
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Negres, Raluca A.; Przhonska, Olga V.; and Hagan, David J., "The Nature Of Excited-State Absorption In Polymethine And Squarylium Molecules" (2001). Scopus Export 2000s. 181.