J-aggregate

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1,1’-diethyl-2,2’-cyanine chloride (pseudoisocyanine chloride, PIC chloride)
Fiber-like J-aggregates (yellow) and light-guiding microcrystallites (red)

A J-aggregate is a type of dye with an absorption band that shifts to a longer wavelength (bathochromic shift) of increasing sharpness (higher absorption coefficient) when it aggregates under the influence of a solvent or additive or concentration as a result of supramolecular self-organisation.[1] The dye can be characterized further by a small Stokes shift with a narrow band, the J in J-aggregate refers to E.E. Jelley who discovered the phenomenon in 1936,[2][3] the dye is also called a Scheibe aggregate after G. Scheibe who also independently published on this topic in 1937.[4][5]

Scheibe and Jelley independently observed that in ethanol the dye PIC chloride has two broad absorption maxima at around 19,000 cm−1 and 20,500 cm−1 (526 and 488 nm respectively) and that in water a third sharp absorption maximum appears at 17,500 cm−1 (571 nm). The intensity of this band further increases on increasing concentration and on adding sodium chloride; in the oldest aggregation model for PIC chloride the individual molecules are stacked like a roll of coins forming a supramolecular polymer but the true nature of this aggregation phenomenon is still under investigation. Analysis is complicated because PIC chloride is not a planar molecule, the molecular axis can tilt in the stack creating a helix pattern. In other models the dye molecules orient themselves in a brickwork, ladder, or staircase fashion; in various experiments the J-band was found to split as a function of temperature, liquid crystal phases were found with concentrated solutions and CryoTEM revealed aggregeate rods 350 nm long and 2.3 nm in diameter.

J-aggregate dyes are found with polymethine dyes in general, with cyanines, merocyanines, squaraine and perylene bisimides. Certain π-conjugated macrocycles, reported by Swager and co-workers at MIT, were also found to form J-aggregates and exhibited exceptionally high photoluminescence quantum yields.[6]

In H-aggregates a hypsochromic shift is observed with low or no fluorescence.

References[edit]

  1. ^ Würthner, F., Kaiser, T. E. and Saha-Möller, C. R. (2011), J-Aggregates: From Serendipitous Discovery to Supramolecular Engineering of Functional Dye Materials. Angewandte Chemie International Edition, 50: 3376–3410. doi:10.1002/anie.201002307
  2. ^ Spectral Absorption and Fluorescence of Dyes in the Molecular State EDWIN E. JELLEY Nature 138, 1009-1010 (12 December 1936) doi:10.1038/1381009a0
  3. ^ Nature 139, 631 (10 April 1937) | doi:10.1038/139631b0 Molecular, Nematic and Crystal States of I: I-Diethyl--Cyanine Chloride EDWIN E. JELLEY
  4. ^ Naturwissenschaften Volume 25, Number 5, 75, doi:10.1007/BF01493278 Polymerisation und polymere Adsorption als Ursache neuartiger Absorptionsbanden von organischen Farbstoffen G. Scheibe, L. Kandler and H. Ecker
  5. ^ Über die Veränderlichkeit der Absorptionsspektren in Lösungen und die Nebenvalenzen als ihre Ursache G. Scheibe Angewandte Chemie Volume 50, Issue 11, pages 212–219, 13. März 1937
  6. ^ Chan, Julian M. W.; Tischler, Jonathan R.; Kooi, Steve E.; Bulovic, Vladimir; Swager, Timothy M. (2009). "Synthesis of J-Aggregating Dibenz[a,j]anthracene-Based Macrocycles". J. Am. Chem. Soc. 131: 5659–5666. doi:10.1021/ja900382r.