Merocyanine dyes
Synthesis, properties, application
m
Eugenij Poronik
Introduction
Brooker’s merocyanine
J Am Chem Soc 73 (1951) 5326
Merocyanine 540
• Merocyanine dyes are considered as a superposition of neutral (I) and zwitterionic (III) forms.
• There is an ideal state, so-called “cyanine limit”, which relates to equal contributions of the polyene-type and the
zwitterionic resonance structures.
• Merocyanines in the cyanine limit are also dyes with most favorable absorption properties, that is, intense
absorption bands at the longest possible wavelength for a given polymethine chain, and they possess enhanced
thermal and photochemical stability owing to equalized bond orders
2
Synthesis
Simple Merocyanines (n = 0)
87%
J Am Chem Soc 73 (1951) 5326
50%
Bull Korean Chem Soc 24 (2003) 569
Zeromethine merocyanines (n = 0) are commonly prepared by the reaction of nitrogen heterocycles
containing a leaving group with active methylene bases.
3
J Chem Soc, Perkin Trans 2 (1997) 1055
Tetr. Lett 39 (1998) 1763
4
Merocarbocyanines (n = 1)
Russ Chem Bull, Int Ed 54 (2005) 2417
Dyes Pigm 60 (2004) 215
Dyes Pigm 58 (2003) 83
J Mater Chem 9 (1999) 2991
The classical route for the synthesis of merocarbocyanine dyes is a reaction of heterocyclic enamines or
corresponding salts with hydroxybenzaldehydes or their heterocyclic analogs.
5
Dyes Pigm 58 (2003) 83
The capability of merocyanines to produce salts is used for their isolation
6
Using of aldehyde analogous
A versatile method for the preparation of merocyanine dyes involves the treatment of methylsubstituted quaternary salts of nitrogen heterocycles with anilinomethylene derivatives of heterocyclic
ketones.
7
Acetanilidomethylene-substituted heterocycles are useful, versatile synthones, and they have been
extensively used for the preparation of merocyanine dyes
8
Dimethylaminomethylene derivatives prepared by treatment of carbo and heterocyclic ketones with
DMF-DMA or with DMF in acetic anhydride have been used for the synthesis of various merocyanine
dyes
9
Tetr. Lett. 42 (2001) 6129
This reaction is suitable for the preparation of symmetrical merocyanines (ketocyanines), difunctionalized
ketones are condensed with two equivalents of quaternary salt
Russ Chem Bull 45 (1996) 164
10
From w-aldehydes
Org Lett 5 (2003) 3143
Angew Chem Int Ed 36 (1997) 2765
The condensation of w-aldehydes with active methylene compounds in in the absence of the base leads to
merocyanines in moderate yields
J Am Chem Soc 121 (1999) 8146
Aza derivatives of w-aldehydes are the most utilized starting materials for the preparation of merocyanine dyes
since the first merocyanine syntheses
11
Synthesis (1999) 2103
Angew Chem Int Ed 38 (1999) 1649
 A versatile one-pot synthesis of merocyanines based on multi-step reaction of nitrogen heterocycles
with active methylene compounds and DMF in acetic anhydride [45, 59].
 The process is uninfluenced by impurities in starting compounds, including water, and can be used in
combinatorial synthesis.
12
51%
Tetrahedron 55 (1999)14421
13
Heterocycl Commun 11 (2005) 129
14
Long-Bridge Merocyanines
J Chem Soc, Faraday Trans 93 (1997) 3653
Similar methodology as utilized for the synthesis of simple merocyanines is useful for the
preparation of their cyclic higher vinilogues.
15
J Appl Spectroscopy 71(2004) 641
16
Structure and Isomerization
• Merocarbocyanines can exist as four transoid isomers with regard to two double bonds of the bridge
fragment.
17
Solvatochromism
Acetone, 96 % ethanol, acetic acid, water, DMF, acetonitrile, 2-propanol, methanol, THF and DMSO
Solvatochromic merocyanines exhibit bathochromic or hypsochromic shifts in solvents of various polarities. Other
characteristics such as dipole moments, fluorescence, and NLO properties change as well.
18
Ion Sensors
Titration with Ni2+
19
Anal Chim Acta 504 (2004) 227
Calcium-sensitive chromogenic crown ethers.
The water-soluble dye (R = CH3) can be used for calcium ion sensing in solution while lipophilized
derivative (R = C12H25) has been successfully applied to ion-exchange type optode PVC membranes.
20
Molecular Aggregation
 Molecular aggregates are self-assemblies of molecules by non-covalent interactions.
 They have significant technological applications such as molecular optoelectronic devices,
fluorescence probes for mitochondrial membrane, and as models of antenna systems that
function to transfer energy and electrons in biological systems
21
Langmuir 20 (2004) 5718-5723
Aggregation processes of merocyanine dyes on lyposomes (artificial cell membranes)
22
Spiropyrans
23
3D data storage media
Schematic representation of a cross-section through a 3D
optical storage disc (yellow) along a data track (orange
marks). Four data layers are seen, with the laser currently
addressing the third from the top. The laser passes through
the first two layers and only interacts with the third, since
here the light is at a high intensity.
No commercial product based on 3D optical data storage has yet arrived on the mass market, although
several companies are actively developing the technology and claim that it may become available "soon".
24
Photodynamic therapy
Merocyanine 540
J Photochem Photobiol B 32 (1996) 27-32
25
Non-linear properties
O
CN
N
N
N
CN
O
d = 115 GM
N
N
CN
Ph
O
N
Ph
O
d = 25 GM
Ph
N
N
CN
N
Ph
O
N
O
d = 35 GM
d = 125 GM
at 1064 nm
Optics Commun 281 (2008) 6072-6079
26
n = 1; dmax = 2300 GM (at 826 nm)
n = 2; dmax = 5000 GM (at 900 nm)
n = 3; dmax = 10000 GM (at 980 nm)
J. Mater. Chem. 19 (2009) 7503–7513
27
Conclusions
 Merocyanine dyes with nitrogen donor and carbonyl acceptor fragments have
found a wide application in various areas of science and technology, including
optical and fluorescent sensors, silver halide photography, optical data storage,
and photodynamic therapy.
 The synthetic methods on merocyanines preparation allow to obtain dyes with a
wide variety of electron donor and acceptor parts, and hence with various
properties.
 Recent progress in computer science and nanotechnology have stimulated new
investigations, including the studies in non-linear optics, and new areas of
medicine.
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Thank you for your
attention