Ultrafast dynamics of excited state of phenoxy-phthalocyanines in
solution
Cheng-Bao Yao
a,
n
, Xiao-Yan Yan
a
, Da-Wei Sun
a
, Yan-Li Sui
a
, Jin Li
b
, Wen-Jun Sun
a
,
Qiang-Hua Li
a,
n
, Shou-Bin Yang
a,
n
a
Key Laboratory of Photonic and Electric Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University,
Harbin 150025, China
b
College of Information Science and Engineering, Northeastern University, Shenyang 110819, China
article info
Article history:
Received 12 April 2015
Received in revised form
11 July 2015
Accepted 27 July 2015
Keywords:
Phthalocyanines
Nonlinear optics
Ultrafast measurements
abstract
Ultrafast dynamics of the excited state of 2,9,16,23-phenoxy-phthalocyanine (Pc1) and 2,9,16,23-phe-
noxy-phthalocyanine-zinc (Pc2) has been investigated using femtosecond transient absorption (TA) and
time-resolved fluorescence (TRFL) techniques. The observed dynamics of femtosecond TA and TRFL ex-
periments are similar, which demonstrated the intrinsic properties of the excitation and the relaxation
processes in both kinds of phthalocyanines with two decay components. A multi level model has been
proposed to explain the photophysical processes after Soret-band excitation. The results show that the
fast decay component dynamics comes from the intramolecular vibrational relaxation, the slower ones
from the internal conversion. The samples are expected to be a potential candidate for optical applica-
tions and photodynamic therapy.
& 2015 Elsevier Ltd. All rights reserved.
1. Introduction
Phthlocyanines (Pcs) and metallophthalocyanines (MPcs) have
aroused intense research interest since the first synthesis in 1907
[1]. Owing to their high stability under intense heat and light, the
properties of diversity, coordinating easily with metal element,
and unique 18
π
-electron delocalization system. These compounds
exhibit large nonlinear susceptibilities, which lead to potential
applications in a variety of new technology fields, including non-
linear optics [2], electrochromic display devices [3], liquid crystals
[4], and so on. Pcs are promising nonlinear optical material with
high dielectric constant, fast response time (femtosecond scale),
easily integrating into optical components and intense absorption
in the near-IR region [5–7], which lead to their potential applica-
tions in photonic [8,9], data processing [10], optical switching [11],
optical limiting [12,13], photodynamic therapy (PDT) [14,15].In
particular, zinc phthalocyanine complexes have attracted much
interest because of their intense absorption in the red region of
visible light, appreciably long triplet lifetimes (microsecond
scales), enhanced fluorescence and singlet oxygen producing
properties, which prompted their roles in the detection and
treatment of tumors in PDT [16] and enhanced fluorescence
imaging performance of hydrophobic colloidal ZnO nanoparticles
by a facile method [17]. The MPcs can be modulated by changing
the peripheral and non-peripheral substituents on the ring in
addition to changing the central metal and the axial ligands. Many
photochemical and photophysical properties of molecules depend
on the kinetics of excited-state processes after the photon ab-
sorption. Therefore, it is important to understand how excited
states behave as a function of time. The conventional view of this
temporal evolution indicates that photoreactivity is largely dic-
tated by the characteristics of the lowest energy excited state of a
molecule. Thus, higher energy excited states are presumed to
convert to this lowest energy state and remove any functional role
from photochemical and photophysical transformations. The
nonlinear optical materials modified from phthalocyanine are in-
creasingly being developed and researched.
In a previous report, we studied the synthesized 2,9,16,23-
phenoxy-phthalocyanine (Pc1) and 2,9,16,23-phenoxy-phthalo-
cyanine-zinc (Pc2) using the reported methods [18]. Moreover, we
have investigated some interesting third-order nonlinear optical
(NLO) properties of Pc1 and Pc2 at 800 nm using femtosecond
pulses and revealed the singular nonlinear absorption properties
and large NLO coefficients [19]. Several other groups have also
demonstrated their potential applications, such as two-photon
imaging, 3D-optical memory, and ultrafast switches. Two-photon
absorption (TPA) was the dominant mechanism in experiment, but
one cannot rule out the presence of excited state absorption from
first excited singlet state (S
1
) to second excited singlet state (S
2
)
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/optlastec
Optics & Laser Technology
http://dx.doi.org/10.1016/j.optlastec.2015.07.019
0030-3992/& 2015 Elsevier Ltd. All rights reserved.
n
Corresponding authors.
E-mail addresses: yaochengbao5@163.com (C.-B. Yao),
qianghua_li@163.com (Q.-H. Li), hagongda2011@126.com (S.-B. Yang).
Optics & Laser Technology 76 (2016) 53–57