The nature of excited-state absorption in polymethine andsquarylium molecules

摘要

Subpicosecond transient absorption measurements were performed fornseveral polymethine and squarylium dyes in ethanol solution and anpolymeric host over the spectral range 400-1500 nm. A variety ofnnonlinear effects including saturable absorption, reverse saturablenabsorption, and gain were observed and analyzed. We observe strongnexcited-state absorption (ESA) in all dyes in the range 450-600 nm. Wenalso report the first prediction and observation of additional ESA bandsnin the near-infrared range. The predictions were based on quantumnchemical calculations and the ESA experiments were performed withnfemtosecond pump-continuum probe techniques. For polymethine dyen2-[2-[3-[(1,3-dihydro-3,3-dimethyl-1-phenyl-2H-indol-2-ylidene)nethylidene]-2-phenyl-1-cyclohexen-1-yl]ethenyl]-3,3-dimethyl-1-phenylindonlium perchorate, an additional ESA band was detected near 1250 nm, andnfor squarylium dyen1,3-Bis-[(1,3-dihydro-1-butyl-3,3-dimetyl-2H-benzo[e]indol-2-ylidene)methnyl]squ araine, two additional ESA bands were found around 870- andn1380-nm, respectively. To further study the nature of these transitions,nthe steady-state excitation anisotropy was also studied and comparednwith predictions. The relationship between ESA spectra of organic dyesnand their molecular structure is discussed