Enhanced reverse saturable absorption of
electrostatic self-assembled layer by layer films
containing (8-quinolineoxy-5-sulfonic acid)
phthalocyanine cobalt and graphene oxide†
Bowen Chen,
a
Chunying He,
*
a
Weina Song,
ab
Cheng Zhao,
a
Yachen Gao,
a
Zhimin Chen,
a
Yongli Dong,
ab
Yiqun Wu
a
and Rong Li
a
Multilayer films containing a-CoPc(QnSO
3
Na)
4
(CoPc), polydiallydimethyldiallylammonium chloride (PDDA)
and graphene oxide (GO) were fabricated through electrostatic self-assembled layer by layer (LBL)
technique. UV-Vis spectroscopy was used to characterize the assembly process. Raman spectroscopy,
scanning electron microscopy (SEM) and atomic force microscopy (AFM) were utilized to explore the
microstructure of the film. The third-order nonlinear properties of the film were studied by Z-scan
measurements at 532 nm with 4 ns pulses. When excited by laser with the input intensity of 1.16 mJ, the
25 bilayer CoPc/GO film exhibits strong reverse saturable absorption (RSA) effect. The nonlinear
absorption coefficient b value is 1.6 10
5
mW
1
, which is 5 and 3 orders larger than that of CoPc
solution sample and grapheme oxide solution sample, and 1.5 times larger than that of the 35 bilayer
CoPc/PDDA film. And also, combination of UV-Vis spectroscopy with Raman spectroscopy was adopted
to analyze the enhancement mechanism of nonlinear optical absorption of the film.
Introduction
The development of photonic and optoelectronic technologies
relies on the new nonlinear optical (NLO) materials including
inorganic crystals, metal clusters, polymers, C
60
, phthalocya-
nines, etc.
1–5
Past research shows that materials with p conju-
gated system oen exhibit strong third-order NLO properties,
which can be used as candidates in optical switching devices.
Optical switching is a fundamental building block of informa-
tion processing, and has been reported in various materials,
such as phthalocyanines
6,7
and graphene oxide.
8,9
In recent
years, graphene-based materials show great promise in ultrafast
lasers as saturable absorbers due to their ultrafast carrier
relaxation times and broadband NLO responses to nanosecond
pulses from the visible to the near-infrared regime.
10–12
GO has
covalently bounded epoxide and hydroxyl functional groups on
either side of its basal plane with carboxyl groups only at the
edge sites. These hydrophilic groups make GO easily connect
with other functional materials, such as nanoparticles,
porphyrins, and pthalocyanines.
13–16
GO sheets contain a
mixture of electronically conducting sp
2
clusters, sp
2
congu-
rations and insulating sp
3
carbon matrix,
17,18
which make GO
displaying excellent third-order NLO properties under nano-
second, picosecond, and femtosecond laser excitation at the
wavelength of 532 nm and 1064 nm.
19–21
Calculations based on
Gaussian and time-dependent (TD) density functional theory
(DFT) about the band gaps of sp
2
cluster and sp
3
carbon matrix
in GO sheets are around 0.5 eV and 2.7–3.1 eV, respectively,
resulting in saturable absorption (SA) effect and excited state
absorption (ESA) eff ect.
19,20,22
Composite materials based on GO
have been fabricated, and their third-order NLO properties were
tuned by controlling the ratio of sp
2
/sp
3
carbons.
23–25
Because of the signicant p-electron conjugation, high
architectural exibility and fast NLO response times, phthalo-
cyanines and their derivatives have emerged as the important
class of materials for NLO applications.
26,27
Naturally, it became
one kind of the most important materials which could attach to
GO and affect the NLO properties of GO. Indeed, it is expected
that the combination of graphene and active phthalocyanine
molecules would afford species that possess not only the
intrinsic properties of phthalocyanine and GO, but also multi-
functional materials with enhanced the third-order NLO
responses compared with that of the individual graphene and
phthalocyanine. Some hybrids based on both graphene and
phthalocyanines with excellent NLO properties have been
reported.
28,29
However, above NLO performance of GO and its
composite materials has been most investigated in the liquid
a
Key Laboratory of Functional Inorgani c Material Chemistry, Ministry of Education,
School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080,
PR China. E-mail: chunyinghe_hlju@163.com; Fax: +86 451 8667 3647
b
College of Environmental and Chemical Engineering, Heilongjiang University of
Science and Technology, Harbin 150022, PR China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra04988a
Cite this: RSC Adv.,2015,5,55150
Received 21st March 2015
Accepted 9th June 2015
DOI: 10.1039/c5ra04988a
www.rsc.org/advances
55150 | RSC Adv.,2015,5,55150–55157 This journal is © The Royal Society of Chemistry 2015
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