Journal
JOURNAL OF LUMINESCENCE
Volume 128, Issue 12, Pages 1927-1936Publisher
ELSEVIER
DOI: 10.1016/j.jlumin.2008.06.002
Keywords
Polymethine; Structure-property relations; Solvatochromism; Quantumchemical analysis; Symmetry breaking; Absorption; Fluorescence; Cyanine; Terminal groups; Squaraine; Tetraone; Organic dyes; Visible; Near infrared; Red shift; Solvent-dependent; Chromophore; Charge delocalization; Weak fluorescence; Excited states
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Funding
- National Science Foundation [ECS 0524533]
- US Army Research Laboratory [W911 NF0420012]
- US Army Research Office [50372-CH-MUR]
- Office of Naval Research [MORPH N00014-06-1-0897]
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We performed a detailed experimental investigation and quantum-chemical analysis of a new series of near IR polymethine dyes with 5-butyl-7,8-dihydrobenzo[cd]furo[2,3-f]indolium terminal groups. We also synthesized and studied two neutral dyes, squaraine and tetraone, with the same terminal groups and performed a comparison of the spectroscopic properties of this set of near IR dyes (polymethine, squaraine, and tetraone) with an analogous set of visible dyes with simpler benzo[e]indolium terminal groups. From these measurements, we find that the dyes with dihydrobenzo[cd]furo[2,3-f]indolium terminal groups are characterized by a remarkably large shift approximate to 300nm (approximate to 200nm for tetraone) of their absorption bands towards the red region. We discuss the difference in electronic structure for these molecules and show that the near IR dyes are characterized by an additional weak fluorescence band from the higher lying excited states connected with the terminal groups. Absorption spectra for the longest polymethines are solvent-dependent and are characterized by a broadening of the main band in polar solvents, which is explained by ground state symmetry breaking and reduced charge delocalization within the polymethine chromophore. The results of these experiments combined with the agreement of quantum chemical calculations moves us closer to a predictive capability for structure-property relations in cyanine-like molecules. (c) 2008 Elsevier B.V. All rights reserved.
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