Incorporation of a ferrocene unit in the π-conjugated structure of donor-linker-acceptor (D-π-A) chromophores for nonlinear optics (NLO)

Article abstract of DOI:10.1016/j.dyepig.2018.03.029

In this paper we describe the synthesis, the electrochemical behaviour as well as the linear and nonlinear optical (NLO) properties of two push-pull derivatives bearing pyranylidene electron donating fragment, pyrimidine/methyl pyrimidinium electron withd

Full text of DOI:10.1016/j.dyepig.2018.03.029

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Incorporation of a ferrocene unit in the π-conjugated structure of donor-linker-
acceptor (D-π-A) chromophores for nonlinear optics (NLO)
Raphaël J. Durand, Sylvain Achelle, Sébastien Gauthier, Nolwenn Cabon, Maxime
Ducamp, Samia Kahlal, Jean-Yves Saillard, Alberto Barsella, Françoise Robin-Le
Guen
PII:
S0143-7208(18)30275-4
10.1016/j.dyepig.2018.03.029
DYPI 6614
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 5 February 2018
Revised Date: 14 March 2018
Accepted Date: 14 March 2018
Please cite this article as: Durand RaphaëJ, Achelle S, Gauthier Sé, Cabon N, Ducamp M, Kahlal S,
Saillard J-Y, Barsella A, Robin-Le Guen Franç, Incorporation of a ferrocene unit in the π-conjugated
structure of donor-linker-acceptor (D-π-A) chromophores for nonlinear optics (NLO), Dyes and Pigments
(2018), doi: 10.1016/j.dyepig.2018.03.029.
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ACCEPTED MANUSCRIPT
Incorporation of a ferrocene unit in the π-conjugated structure of donor-linker-acceptor
(D-π-A) chromophores for nonlinear optics (NLO)
Raphaël J. Durand,[a] Sylvain Achelle,*[a] Sébastien Gauthier,*[a] Nolwenn Cabon,[a] Maxime
Ducamp,[a] Samia Kahlal,[a] Jean-Yves Saillard,[a] Alberto Barsella,[b] and Françoise Robin-Le
Guen[a]
[a] Univ. Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) - UMR 6226, F-
35000 Rennes, France. E-mails: sebastien.gauthier@univ-rennes1.fr, sylvain.achelle@univ-
rennes1.fr, Tel:+33 2 96 46 93 44, +33 2 96 46 94 48
[b]
Département d'Optique ultrarapide et Nanophotonique, IPCMS, UMR CNRS 7504,
Université de Strasbourg, 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France.
Abstract
In this paper we describe the synthesis, the electrochemical behaviour as well as the linear and
nonlinear optical (NLO) properties of two push-pull derivatives bearing pyranylidene electron
donating fragment, pyrimidine/methyl pyrimidinium electron withdrawing moiety and a
ferrocene part in the π-conjugated bridge. The properties of these two compounds were
compared to their analogues without ferrocene or pyranylidene fragments. Experimental
results were completed with DFT calculations to gain further insight into the intramolecular
charge transfer (ICT). All the results indicate a significant charge transfer through the
ferrocene unit. The ICT is however more limited than in all organic analogues.
1. Introduction
The development of organic and organometallic second order nonlinear optical (NLO)
chromophores has been an intensive research subject due to their potential in key field such as
photonic1–4 and electro-optics.5–9 Key applications of second order NLO chromophores
1

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include optical signal processing, integrated optics and second harmonic generation (SHG)
microscopy. In comparison with inorganic NLO crystals such as lithium niobate, organic or
organometallic NLO chromophores have many advantages such as a lower cost, larger and
faster NLO responses.10–12
Second order NLO properties require the absence of centrosymmetry and generally the
second order NLO chromophores are based on an electron-donating group (D) and an
electron-withdrawing group (A) linked by a π-conjugated bridge (D-π-A).10–15 NLO
properties are directly related to the intramolecular charge transfer (ICT) occurring in such
structures and can be easily tuned by varying the nature of the donor/acceptor couple and the
π-conjugated spacer.16–18
In our group, we have recently optimized the NLO properties of chromophores based on
pyrimidine19–24 and/or pyranylidene22–27 moieties as electron-withdrawing and electron-
donating fragments respectively. It has been shown that pyrimidine and methylated
pyrimidinium salts exhibit higher electron-withdrawing character than well-known pyridine
analogues.28 Proaromatic pyranylidene moieties, capable of gaining aromaticity upon ICT
process into the push-pull structure, are now well-established electron-donating groups.25,29–32
The ferrocene moiety has been extensively used as electron-donating part of NLO
chromophores.13,33–37 Ferrocene exhibits a good thermal and photochemical stability and the
possibility of redox switching at low redox potential.38,39 Ferrocene has rarely been used as
spacer between donor and acceptor parts of push-pull molecules even if electron-transfer
through the ferrocene has been demonstrated.40–42 In this case, the charge transfer occurs
"through space" and represents an alternative molecular strategy for NLO chromophores.43,44
1,1'-disubstituted ferrocenes with aromatic or alkynyl substituents generally adopt a stacked
syn-conformation due to the electronic preference of the ferrocene and favorable π-π
2

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interactions.40,45,46 However, it has been shown that the introduction of charges to the
ferrocene substituents can induce rotation to the anti-conformation.47,48
In continuation of our work regarding the incorporation of metal centers in the π-conjugated
core of push-pull chromophores,23,24 in this contribution we describe the synthesis,
electrochemical, photophysical and second order NLO properties of two chromophores 1 and
2 with the following structure: D-π-Fc-π-A (Chart 1). In order to study the influence of the
ferrocene units, the properties of these compounds will be compared with their D-π-A organic
analogues 3 and 4 and Fc-π-A chromophores 5 and 6 in which the ferrocene plays the role of
electron-donating group.
Chart. 1
2. Results and discussion
2.1. Synthesis
The asymmetrical ferrocene complex 1 was obtained in two steps. A Wittig reaction was first
carried out with stoichiometric amounts of 1,1’-ferrocenedicarboxaldehyde and pyranylidene
phosphonium salt49 to give compound 7.50 The second carbonyl group reacted with 4-
methylpyrimidine through a Knoevenagel condensation to form a trans-alkene, according to a
procedure already described19 (Scheme 1). The compounds 1, 351 and 519 could easily be
3