Diphenylamine end-capped 1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) derivatives with large two-photon absorption cross-sections and strong two-photon excitation red fluorescence

Article abstract of DOI:10.1039/b911808j

Novel donor-π-bridge-acceptor-π-bridge-donor (D-π-A-π-D)-type 1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) derivatives with end-capping diphenylamine groups have been synthesized and shown to exhibit large two-photon absorption cross-sections over a wide range of wavelengths with strong two-photon excitation red fluorescence.

Full text of DOI:10.1039/b911808j

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Diphenylamine end-capped 1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole
(DPP) derivatives with large two-photon absorption cross-sections and
strong two-photon excitation red fluorescencew
Er Qian Guo, Pei Hua Ren, Yan Li Zhang, Hai Chang Zhang and Wen Jun Yang*
Received (in Cambridge, UK) 16th June 2009, Accepted 22nd July 2009
First published as an Advance Article on the web 11th August 2009
DOI: 10.1039/b911808j
Novel donor–p-bridge–acceptor–p-bridge–donor (D–p–A–p–D)-
type 1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) derivatives
with end-capping diphenylamine groups have been synthesized
and shown to exhibit large two-photon absorption cross-sections
over a wide range of wavelengths with strong two-photon
excitation red fluorescence.
Organic molecules exhibiting large two-photon absorption
(TPA) cross-sections (d) have received increasing attention
owing to potential applications in three-dimensional (3-D)
fluorescence imaging,1 optical power limitation,2 lasing
up-conversion,3 3-D optical data storage,4 3-D microfabrication5
and photodynamic therapy.6 A variety of compounds exhibiting
large d, including donor–acceptor–donor (D–A–D)-type
molecules, donor–p-bridge–acceptor (D–p–A)-type molecules,
donor–p-bridge–donor (D–p–D)-type molecules, macrocycles,
Scheme 1 Synthetic routes and structure of DPP-based two-photon
dendrimers, polymers and multi-branched compounds, have
dyes.
been synthesized and their structure–property relationships
investigated.7 However, most of them employ CQC bonds as
Recently, attempts have been made to use DPP-based
polymers as highly luminescent,11 electroactive12 and
photoactive13 materials in optoelectronic devices. We considered
DPP may be a useful p-center for TPA fluorophores.
However, to the best of our knowledge, there are no reports
on the synthesis and TPA properties of DPP-based derivatives.
In this work, we connect electron-donating diphenylamine and
triphenylamine groups to the 3,6-positions of electron-
withdrawing pyrrolo[3,4-c]pyrrole-1,4-dione via 1,4-phenylene
conjugation bridges to form novel D–p–A–p–D-type TPA
dyes (DPP-DPA and DPP-TPA, Scheme 1). The results show
that these DPP-based conjugated molecules exhibit large TPA
cross-sections (dmax = 900–1200 GM) and emit strong
(F = 0.35–0.47) red two-photon excitation fluorescence
(TPEF, lem = 594–608 nm). The dmax values of these DPP
derivatives are not only comparable with two-photon
chromophores having aromatic rings as conjugation bridges
reported in the literature,9,14 but also comparable with those of
the similar sized chromophores with CQC and CRC bonds
as conjugation bridges.7 In addition, we have found that DPP
itself (DPP-R) has a comparable d. These results demonstrate
that DPP is a novel and efficient p-center for the construction
of two-photon chromophores with strong red emissions.
To synthesize DPP-DPA and DPP-TPA, 3,6-bis(4-bromo-
phenyl)pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) was firstly
prepared by the reaction of diisopropyl succinate with 2 mol
equiv. of 4-bromobenzonitrile in the presence of t-amyloxide
sodium. Subsequently, DPP was converted to soluble DPP-R
conjugation bridges and emit blue and green fluorescence.
Although CQC bonds are effective conjugation bridges, they
readily undergo trans–cis photoisomerization, photooxidation
and photodegradation, which may hamper the efficiency and
lifetime of materials.8 The drawback of CQC bonds can be
avoided if one uses aromatic and heteroaromatic rings as
conjugation bridges. Red emission can be realized in such
molecules, with enhanced intramolecular charge transfer
(ICT) and a large Stokes shift. Recently, Mataka et al.
reported that D–p–A–p–D-type 2,1,3-benzothiadiazole
derivatives with end-capping diarylamine groups showed a
maximal d of 50–200 GM and an orange-red emission excited
under laser wavelengths 600–670 nm.9 However, structurally
stable TPA dyes exhibiting a large d and also emitting strong
red fluorescence via direct two-photon excitation at a longer
wavelength are still scarce at present.
1,4-Diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) and its
derivatives represent a class of brilliant red and strongly
fluorescent high performance pigments that have exceptional
light, weather and heat stability, and a high light fastness.10
Key Laboratory of Rubber-Plastics (QUST), Ministry of Education,
School of Polymer Science & Engineering, Qingdao University of
Science & Technology, 53 Zhengzhou Road, Qingdao, 266042, China.
E-mail: ywjph2004@qust.edu.cn; Fax: +86 532-84023977;
Tel: +86 532-88896092
w Electronic supplementary information (ESI) available: Synthesis
and characteristics of the intermediates and the final compounds.
See DOI: 10.1039/b911808j
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Chem. Commun., 2009, 5859–5861 | 5859

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stronger ICT and the decreased energy gap between the
ground and Franck–Condon states.
The d values were determined by a two-photon-induced
fluorescence measurement technique using femtosecond laser
pulses (160 fs, 1 kHz)15 over a relatively wide range of
wavelengths, which avoids possible complications due to
excited state excitation, The occurrence of non-linear absorption
was confirmed by the linear dependence of the output
fluorescence intensity on the square of the input laser power
(Fig. S1, see the ESIw). The good overlap between one- and
two-photon excitation fluorescence (Fig. 3 and Fig. S2w)
indicates that the emissions occurs from the same excited
state, regardless of the mode of excitation.
Fig. 2 shows that the maximal TPA cross-section (dmax) of
DPP-DPA and DPP-TPA are 1200 and 920 GM, respectively.
These d and d/MW (the TPA cross-section per molecular
weight) values are large and comparable to those of most
chromophores having benzene, anthracene and fluorene as
centers and CQC bonds as conjugation bridges (Table 1).16
The dmax/MW of DPP-DPA and DPP-TPA are 2.98 and 1.68,
respectively, which are valuable because molecules with
Fig. 1 Normalized one-photon absorption (left) and emission (right)
spectra of DPP-based two-photon dyes in chloroform.
by eliminating the intermolecular hydrogen bonds
(NÁ Á ÁHÁ Á ÁO) via N-alkylation of the lactam units. Palladium-
catalyzed C–N bond formation between DPP-R and diphenyl-
amine afforded DPP-DPA. DPP-TPA was by the Suzuki
coupling of DPP-R with triphenylamine boronic acid. The
structures of these DPP-based derivatives were unambiguously
dmax/MW 4 1.0 have been found to be useful for applications
that require strong TPA, such as optical limiting and 3-D
microfabrication, or strong TPEF, such as bioimaging.7b In
addition, we found that DPP itself (DPP-R) emits a strong
1
confirmed by H and 13C NMR spectroscopy and elemental
analysis (see the ESIw).
The normalized one-photon absorption and emission
spectra of DPP-DPA, DPP-TPA and DPP-R in chloroform
are displayed in Fig. 1. Their spectral properties are
summarised in Table 1. The end-capping of DPP-R with
triphenylamine and diphenylamine leads to large bathochromic
shifts from 476 to 508 and 539 nm respectively. This originates
from enhancement of the intramolecular charge transfer (ICT)
between the terminal amino groups and the DPP core induced
by the formation of the D–p–A–p–D configuration. The ICT
effect of DPP-TPA is weaker (smaller red shift) than that of
DPP-DPA, which indicates that the benzene ring is not an
effective conjugation bridge, probably due to the non-planar
biphenyl structure. As expected, DPP-TPA and DPP-DPA
emit red fluorescence because of their strong ICT effects.
Moreover, DPP-DPA shows a large red-shifted emission
(604 nm) with a low fluorescence quantum yield (F = 0.37)
compared to DPP-TPA (595 nm, F = 0.46) as a result of its
Fig. 2 Two-photon spectra of DPP-based two-photon dyes measured
in 2 Â 10À4 M chloroform solutions.
Table 1 One- and two-photon properties of TPA dyes
Compound
l
UV/nma
l
PL/nmb
Dn/cmÀ1c
Fd
l
TPA/nme
d
max/GMf
dmax/MW
DPP-R
DPP-DPA
DPP-TPA
Ph-Hg
476
539
508
408
472
455
587
415
546
604
595
455
525
487
656
457
2650
1930
2880
1040
1700
1440
1790
2210
0.67
0.37
0.46
0.88
0.86
0.78
0.11
0.79
730
810
820
730
835
800
990
740
110
0.31
2.98
1.68
2.70
2.91
2.35
4.41
2.60
1200
930
995
1940
1100
2290
1260
Ph-CNh
An-Hi
An-CNj
F-Hk
a
b
The wavelength of the longest wavelength band in the one-photon absorption spectrum. lmax of the one-photon fluorescence spectrum.
c
d
e
f
Stokes shift. Fluorescence quantum yield. lmax of the TPA spectrum. The peak TPA cross-section in 10À50 cm4 s photonÀ1 (GM).
1,4-Bis(p-dibutylaminostyryl)benzene; the data are taken from ref. 16a. 1,4-Bis(dibutylaminostyryl)-2,5-dicyanobenzene; the data are taken
g
h
i
from ref. 16a. 2,6-Bis(dihexylaminostyryl)anthracene; the data are taken from ref. 16b. 2,6-Bis(dihexylaminostyryl)-9,10-dicyanoanthracene;
k
the data are taken from ref. 16b. 2,7-Bis(dibutylaminostyryl)-9,9-dinonylfluorene; the data are taken from ref. 16c.
j
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Fig. 3 Normalized one-photon absorption (OPE) and two-photon
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with stable chemical structures and measured their TPA
properties using femtosecond laser pulses. They exhibit large
d values and emit strong red fluorescence in a TPA process
that can be attributed to enhanced ICT between the amino
groups and the DPP core. DPP itself also shows a valuable
d value. This work, for the first time, provides a novel
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Financial support for this research was provided by the
NSFC of China (no. 50573036) and the Open Project of State
Key Laboratory of Supramolecular Structure and Materials
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This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 5859–5861 | 5861