Journal
DYES AND PIGMENTS
Volume 77, Issue 3, Pages 525-536Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.dyepig.2007.08.002
Keywords
squarylium; arene; thiophene; NIR dye; absorption spectra; fluorescence emission
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A series of arene- and thiophene-bridged bis-squarylium dyes were synthesized using the corresponding bis-squaric acids as precursors and their electronic absorption and fluorescence emission properties were investigated. The arene-bridged, bis-squarylium dyes exhibited electronic absorption in the visible to near-infrared regions. The combination of the pyrene spacer with the benzindoline heterocycles resulted in significantly red-shifted absorption at 770 nm. The arene-bridged dyes were fluorescence emissive to some extent and some compounds exhibited fluorescence emission in the near-infrared region. Thiophene-bridged dyes, in which thiophene-, bithiophene-, and terthiophene spacers were employed, displayed electronic absorption in the near-infrared region from 717 to 807 nm; an increase in the number of thiophene rings in the spacer led to a blue shift of the absorption maxima due to disruption of pi-electron conjugation. The thiophene-bridged dyes exhibited fluorescence emission in the near-infrared region, although the fluorescence intensities were much smaller than those of the fluorescent squarylium dye. (c) 2007 Elsevier Ltd. All rights reserved.
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