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\begin{document}

\title{Long-Lasting Chemiluminescence by Aggregation-Induced Emission
Surfactant with Ultralow Critical Micelle Concentration}



\author[1]{Youkai Yu}%
\author[1]{Zhiqin Yuan}%
\author[2]{Chao Lu}%
\affil[1]{Beijing University of Chemical Technology}%
\affil[2]{Affiliation not available}%


\vspace{-1em}



  
  \date{May 05, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
The development of green and simple chemiluminescence (CL) systems with
intensive and long-lasting emission is highly desirable in lighting and
extension of their applications. In this study, it is found that the
involvement of aggregation-induced emission (AIE) surfactant could
greatly enhance the CL of luminol--H2O2--Co2+ system. The inserted
hydrophobic tetraphenylethylene fluorophore in AIE is able to increase
the hydrophobicity of alkyl chain and decrease the critical micelle
concentration (CMC) of surfactant. The synergistic effect of
micelle-improved enrichment and CL resonance energy transfer endows
luminol--H2O2--Co2+ system intensive and long-lasting emission under
neutral pH conditions (pH 7.4). The visible emission is still observed
even after 60 min. Our study has opened a new avenue for exploring green
and simple effective CL systems through AIE surfactant with unltralow
CMC toward various applications in lighting, optical sensing, and
photocatalysis, etc.%
\end{abstract}%



\sloppy


Long-Lasting Chemiluminescence by Aggregation-Induced Emission
Surfactant with Ultralow Critical Micelle Concentration

Youkai Yu,\textsuperscript{1}Zhiqin Yuan*\textsuperscript{,1} and Chao
Lu*\textsuperscript{,1,2}

\textsuperscript{1} Y. Yu, Dr. Z. Yuan and Prof. Dr. C. Lu State Key
Laboratory of Chemical Resource Engineering, College of Chemistry,
Beijing University of Chemical Technology, Beijing 100029, China

E-mail: yuanzq@mail.buct.edu.cn (Z. Yuan), luchao@mail.buct.edu.cn (C.
Lu). Phone/Fax: +86 10 64411957.

\textsuperscript{2} Prof. Dr. C. Lu Green Catalysis Center, and College
of Chemistry, Zhengzhou University, Zhengzhou 450001, China

Keywords: long-lasting chemiluminescence, fluorescent surfactant,
aggregation-induced emission

The development of green and simple chemiluminescence (CL) systems with
intensive and long-lasting emission is highly desirable in lighting and
extension of their applications. In this study, it is found that the
involvement of aggregation-induced emission (AIE) surfactant could
greatly enhance the CL of
luminol--H\textsubscript{2}O\textsubscript{2}--Co\textsuperscript{2+}system.
The inserted hydrophobic tetraphenylethylene fluorophore in AIE is able
to increase the hydrophobicity of alkyl chain and decrease the critical
micelle concentration (CMC) of surfactant. The synergistic effect of
micelle-improved enrichment and CL resonance energy transfer endows
luminol--H\textsubscript{2}O\textsubscript{2}--Co\textsuperscript{2+}system
intensive and long-lasting emission under neutral pH conditions (pH
7.4). The visible emission is still observed even after 60 min. Our
study has opened a new avenue for exploring green and simple effective
CL systems through AIE surfactant with unltralow CMC toward various
applications in lighting, optical sensing, and photocatalysis, etc.

\textbf{1. Introduction}

As a classical cold light, chemiluminescence (CL) has attracted wide
research interest in last decades due to its advantages of free light
source and low background, which makes CL technique essential in the
exploration of lighting systems for various applications, \emph{e.g.} ,
sensing, bioimaging and rescue operations after
disasters.\textsuperscript{1-5} To achieve effective and long-period
lighting, a long-lasting emission system is usually
required.\textsuperscript{6-8} However, most existing CL systems show
flash-type light emission, which hinders their
applications.\textsuperscript{9-11} In contrast, CL systems with strong
intensity and glow-type emission are more charming to the development of
cold light sources. To meet this concern, few CL systems with
sustained-release of reactants have been developed \emph{via}introducing
hydrogel or tablet.\textsuperscript{12,13} For example, Liu\emph{et al}
. reported intensive and long-lasting CL hydrogels by integrating
chitosan, \emph{N} -(4-aminobutyl)-\emph{N} -ethylisoluminol and
Co\textsuperscript{2+}.\textsuperscript{12} With the combination of
luminol tablet and PVP--H\textsubscript{2}O\textsubscript{2} complex
solution, our group constructed a long-lasting (\textasciitilde{}13 h)
CL light using Tris--Co\textsuperscript{2+} complex as the
catalyst.\textsuperscript{13} Nevertheless, the above fabricated systems
were complicated, limiting their wide use. Therefore, it is highly
necessary to explore a simple and long-lasting CL system.

It is reported that typical
luminol--H\textsubscript{2}O\textsubscript{2}--Co\textsuperscript{2+}system
possesses relatively slow CL kinetics under neutral pH
conditions.\textsuperscript{14} Unfortunately, the ultraweak CL
intensity of
luminol--H\textsubscript{2}O\textsubscript{2}--Co\textsuperscript{2+}system
at neutral condition hinders its further application. It is generally
accepted that the introduction of surfactant could enhance CL intensity
of most CL systems.\textsuperscript{15-17} For instance, Xie\emph{et al}
. found that the CL intensity of peroxyoxalate
derivativel--H\textsubscript{2}O\textsubscript{2} system can be greatly
enhanced upon introducing cetyltrimethylammonium bromide (CTAB, a kind
of typical cationic surfactant).\textsuperscript{18} However, the
previous reports demonstrated that the CL promotion was only implemented
with high surfactant concentration, usually above critical micelle
concentration (CMC), and CMCs of conventional surfactants are generally
in mM level.\textsuperscript{19,20} The requirement of high surfactant
concentration is conflicting to the green chemistry and environment
friendly. Therefore, the development of surfactant with low CMC is
required in order to decrease its usage and side effect to environment.

CL resonance energy transfer (CRET) is usually utilized to further
improve CL signals. In this case, additional fluorophores as energy
acceptors are required in conventional surfactant-enhanced CL systems.
For example, Song \emph{et al} . reported the construction of intensive
and long-lasting multicolor CL systems by introducing fluorescein or
rhodamine B as the energy acceptor.\textsuperscript{7} Nevertheless, the
multicomponent involvement results in system complexity and weak
stability. Accordingly, a direct linking of fluorophore into surfactant
would make CL system simple. Hence, the introduction of novel surfactant
with ultralow CMC and CRET acceptor is appealing for a simple and
long-lasting CL system.

Stepanek \emph{et al} . proposed fluorescent block copolymer surfactant
by linking \emph{p} -vinyl-9,10-diphenylanthracene (DPA) into
polystyrene-\emph{block} -poly(methacrylic
acid).\textsuperscript{21}Unfortunately, the aggregation-caused
quenching (ACQ) properties of DPA led to weak fluorescence upon forming
micelle. The ACQ features of the fabricated fluorescent block copolymer
surfactant would restrict its potential applications in CL as the CRET
acceptor. In contrast, aggregation-induced emission (AIE) fluorophores
show bright emission after aggregates.\textsuperscript{22-25} It is
well-known that Tang's group has explored many AIE fluorophres based on
tetraphenylethylene (TPE).\textsuperscript{26-28} By inserting TPE into
the backbone of surfactant, our group has reported a few novel
fluorescent surfactants with ultralow CMC due to the increased
hydrophobicity of alkyl chain (\textless{}60 \selectlanguage{greek}μ\selectlanguage{english}M).\textsuperscript{29-33}
Herein, we described our attempts to apply the developed AIE surfactants
into long-lasting
luminol--H\textsubscript{2}O\textsubscript{2}--Co\textsuperscript{2+} CL
system.\textsuperscript{34} In a case study, we selected the TPE
inserted dodecyltrimethylammonium bromide (4th cationic headgroup,
denoted as C\textsubscript{8}-TPE-C\textsubscript{4}TAB) for the CL
signal enhancement at pH 7.4. The CL intensity revealed 20-fold
increment in the presence of only 80 \selectlanguage{greek}μ\selectlanguage{english}M
C\textsubscript{8}-TPE-C\textsubscript{4}TAB, and glow-type emission
appeared. The enhanced CL and long-lasting emission were due to the
integration of micelle-mediated reactant enrichment and CRET between
luminol and TPE (Figure 1). In other word, the CL reactants were
enriched through electrostatic attraction, which subsequently benefits
the CL reaction and the CRET process. The long-lasting CL was visible to
naked eyes even after 60 min. The proposed fluorescent
surfactant-assisted long-lasting emission showed advantages of
convenient operation, low surfactant consumption and
environment-friendly. The development of simple and green long-lasting
CL systems for analytical sensing or lighting is possible by introducing
novel fluorescent surfactants with ultralow CMCs.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\textbf{Figure 1.} Schematic illustration of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB-mediated intensive and
long-lasting CL emission of the
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system.

\textbf{2. Results and Discussion}

\textbf{C\textsubscript{8}-TPE-C\textsubscript{4}TAB-enhanced CL of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system.}
As a starting point for our study, we synthesized fluorescent surfactant
C\textsubscript{8}-TPE-C\textsubscript{4}TAB according to our previously
reported method and characterized it with\textsuperscript{1}H NMR, MS,
steady-state and time-resolved fluorescence
spectrometry.\textsuperscript{34} All results revealed the successful
preparation of C\textsubscript{8}-TPE-C\textsubscript{4}TAB (Figures
S1-S3). As is known, surfactants could facilitate the CL reaction and
enhance the CL signals.\textsuperscript{35,36} In this study, the CL
signals of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2} in
the absence and presence of C\textsubscript{8}-TPE-C\textsubscript{4}TAB
were recorded under pH 7.4 conditions. As shown in Figure 2, the CL
intensity was dramatically enhanced (\textasciitilde{}20 folds) after
the addition of 80 \selectlanguage{greek}μ\selectlanguage{english}M C\textsubscript{8}-TPE-C\textsubscript{4}TAB,
indicating the feasibility of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB-improved CL intensity of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system.
In addition, the reaction kinetics was also dramatically decelerated in
the presence of C\textsubscript{8}-TPE-C\textsubscript{4}TAB. The
enhanced intensity and extended CL emission kinetics indicated the
possibility to construct long-lasting
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
with the assistance of C\textsubscript{8}-TPE-C\textsubscript{4}TAB.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 2.} CL signals of the
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
in the absence (A) and the presence (B) of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB.

\textbf{CL enhancement in the presence of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB or conventional cationic
surfactant.} As referred in previous work,\textsuperscript{34} the CMC
of C\textsubscript{8}-TPE-C\textsubscript{4}TAB was measured to be 46
\selectlanguage{greek}μ\selectlanguage{english}M. In this case, C\textsubscript{8}-TPE-C\textsubscript{4}TAB existed
as the micelle but not monomer or dimer with 80 \selectlanguage{greek}μ\selectlanguage{english}M concentration.
According to HRTEM measurement (Figure 3A), the formation of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle
(\textasciitilde{}6.2 nm, 100 counts) was observed. These results
demonstrated that the enhanced CL was attributed to the
C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle-promoted CL
reaction. To understand the differences of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle and typical ternary
ammonium micelle promoted CL, the CL signals of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
upon adding C\textsubscript{8}-TPE-C\textsubscript{4}TAB and
cetyltrimethylammonium bromide (CTAB) were measured. The CMC of CTAB is
reported to be 1.0 mM, and thus 2.0 mM CTAB was added to ensure the
formation of CTAB micelle.\textsuperscript{37} The HRTEM results
indicated the formation of micelle with 2.0 mM CTAB (Figure S4). As
shown in Figure 3B, the addition of CTAB largely enhanced the CL
signals, indicating the universality of micelle-promoted CL. However,
the CTAB-induced CL enhancement was lower than that of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB. Since the CTAB
concentration is much higher than that of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB, the CTAB-induced CL
enhancement may depend on its concentration. To understand the
concentration effect, the CL signal of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
were recorded upon adding CTAB with the different concentrations. As
manifested in Figure 3C, the CL signals gradually increased with an
increase in CTAB concentration, and showed a sudden increment around
CMC. Further higher concentrations didn't show dramatic increase of CL.
Therefore, the CTAB concentration with 2-folds of CMC would be enough to
afford the stable micelle conditions.

In order to further figure out the possible reasons of the different CL
enhancement characters, the other conventional cationic surfactants were
tested, including tetradecyltrimethylammonium bromide (TTAB),
dodecyltrimethylammonium bromide (DTAB) and decyltrimethylammonium
bromide (DeTAB). To guarantee the formation of corresponding micelle,
the concentrations of these surfactants were set to be 2-folds of their
CMCs.\textsuperscript{38} The concentrations of TTAB, DTAB, and DeTAB
were 8, 32, and 114 mM, respectively. It was seen that the
micelle-improved CL signals increased with the increasing alkyl chain
length of surfactants (Figure 3D). Upon the addition of cationic
surfactants with short alkyl chain length, even with ultrahigh
concentrations (\textgreater{}30 mM), the CL signals were much lower
than that by adding C\textsubscript{8}-TPE-C\textsubscript{4}TAB (80
\selectlanguage{greek}μ\selectlanguage{english}M). These results suggested that
C\textsubscript{8}-TPE-C\textsubscript{4}TAB was superior to
conventional cationic surfactants on the CL improvement toward
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 3.} (A) HRTEM image of 80 \selectlanguage{greek}μ\selectlanguage{english}M
C\textsubscript{8}-TPE-C\textsubscript{4}TAB. (B) CL signals of the
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
upon adding CTAB and C\textsubscript{8}-TPE-C\textsubscript{4}TAB. (C)
CL signals of the
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
upon adding CTAB with the different concentrations. (D) CL signals of
the
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
upon adding conventional cationic surfactants.

\textbf{Mechanism of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB-mediated intensive and
long-lasting CL emissions.} As indicated above, the addition of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB endowed more effective CL
reaction than conventional cationic surfactants. It is reported that
cationic micelle can adsorb anionic reactants and benefit the CL
reaction.\textsuperscript{39} At pH 7.4, the
C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle was positively
charged (+11.0 mV) because of the outside ternary ammonium cation
(Figure S5), while luminol was negatively charged (--4.8 mV). The
electrostatic attraction between positively charged
C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle and negatively
charged luminol dianion/peroxide anion easily leads to surface
adsorption and enrichment of reactants.\textsuperscript{40-42} Such an
electrostatic attraction-assisted CL emission was also provided by SDS
(sodium dodecyl sulfonate, a kind of typical anionic surfactant). As
shown in Figure S6, the CL intensity of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
distinctly decreased upon adding SDS. This is because the outside
sulfonic acid groups make SDS micelle negatively charged, which
possesses strong electrostatic repulsion toward luminol dianion and
peroxide anion.\textsuperscript{20}

To further understand the mechanism of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB-enhanced CL intensity and
long-lasting emission, a few characterizations were performed. The
generation of reactive oxygen species (ROS) is important to the CL
signals. We tested the CL inhibition with the addition of different ROS
scavengers. As displayed in Figure S7, \emph{p} -benzoquinone (HQ) and
thiourea caused visible CL suppression, while
NaN\textsubscript{3}induced slight CL decrease, suggesting the primary
ROS were superoxide radical (O\textsubscript{2}\textsuperscript{*-}) and
hydroxyl raidical (\textsuperscript{*}OH).\textsuperscript{43,44} The
electron paramagnetic resonance results also demonstrated the continuous
generation of O\textsubscript{2}\textsuperscript{*-}
and\textsuperscript{*}OH during the CL reaction (Figure 4). It is
reported that many ROS possess longer lifetime in hydrophobic
environment.\textsuperscript{45} When inserting TPE into the backbone of
surfactant in this work, the hydrophobicity of alkyl chain increased,
this might benefit the stabilization of ROS and promote the CL reaction.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

\textbf{Figure 4.} Time-dependent EPR spectra of the
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}-C\textsubscript{8}-TPE-C\textsubscript{4}TAB
system.

As mentioned in CTAB concentration study, the formation of micelle plays
important role in enhancing the CL emission. Thus, the total micelle
number would affect the CL reaction. That is, less micelle leads to the
high concentrations of reactants on the surface of micelle, and promotes
the CL emission. In contrast, the average surface concentrations of
reactants decreased with the increasing total micelle number. In this
case, the CL reaction was inhibited and only weak CL emission could be
observed. For C\textsubscript{8}-TPE-C\textsubscript{4}TAB and CTAB
improved
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}systems,
the final concentration of C\textsubscript{8}-TPE-C\textsubscript{4}TAB
and CTAB were 80 \selectlanguage{greek}μ\selectlanguage{english}M and 2.0 mM, respectively. The aggregation number of
micelle was calculated to be 64 in CTAB micelle, while it became 36 in
C\textsubscript{8}-TPE-C\textsubscript{4}TAB
micelle.\textsuperscript{46} The total micelle numbers of CTAB micelle
and C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle were determined
to be 3.8\selectlanguage{ngerman}×10\textsuperscript{15} and 2.3×10\textsuperscript{14},
respectively. The CTAB micelle number was 16-folds higher than that of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle. Obviously, a
single C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle surface
exist more luminol dianion and peroxide anion, which contributes the
higher CL signals.

In addition to high enrichment effect, CRET is also needed be considered
in the CL enhancement of C\textsubscript{8}-TPE-C\textsubscript{4}TAB.
The TPE fluorophore of C\textsubscript{8}-TPE-C\textsubscript{4}TAB
could act as the CRET acceptor, and its AIE characters could avoid the
luminescence quenching during the formation of
micelle.\textsuperscript{47,48} In contrast, CTAB in the absence of
intrinsic fluorophore could not act as the CRET acceptor. Then, the CL
emission spectra of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
with the addition of CTAB or
C\textsubscript{8}-TPE-C\textsubscript{4}TAB were obtained. As shown in
Figure 5A, the emission maximum of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
located at 425 nm upon adding CTAB. The 425 nm light belongs to the
excited luminol radicals.\textsuperscript{49} However, the emission
maximum shifted to 486 nm in the presence of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB (Figure 5B) and the CL
emission spectrum was overlapped with the fluorescence emission profile
of C\textsubscript{8}-TPE-C\textsubscript{4}TAB. The shifted emission
maximum and characterized CL spectrum implied the occurrence of CRET in
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}-C\textsubscript{8}-TPE-C\textsubscript{4}TAB
system.\textsuperscript{50,51} To determine the CRET efficiency (\selectlanguage{greek}φ\selectlanguage{english}), the
integral areas of emission of TPE acceptor (denoted as
I\textsubscript{A}) and total system (denoted as I\textsubscript{T})
were acquired by peak fitting analysis. Based on the equation: \selectlanguage{greek}φ \selectlanguage{english}=
I\textsubscript{A} / I\textsubscript{T}, the \selectlanguage{greek}φ \selectlanguage{english}was calculated to be
94.0\%. As a result, the high enrichment and CRET contributed the
intensive CL of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}-C\textsubscript{8}-TPE-C\textsubscript{4}TAB
system. The schematic illustration of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle-amplified CL was
displayed in Figure 6.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

\textbf{Figure 5.} CL emission spectra of the
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
in the presence of CTAB micelle (A) and
C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle (B). Inset pictures
are the corresponding photographs.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

\textbf{Figure 6.} Schematic illustration of CTAB micelle (left) and
C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle (right) amplified
CL of the
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system.

To understand whether the insert location affected the CL emission, the
CL signals of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
upon adding C\textsubscript{4}-TPE-C\textsubscript{8}TAB (8th cationic
headgroup insert), and TPE-C\textsubscript{12}TAB (12th cationic
headgroup insert) were recorded. As shown in Figure S8A, the CL
intensity decreased as the extended insert location. A possible reason
was due to the decreased CRET efficiency because the distance between
excited luminol and TPE increases with the extended insert location
(Figure S8B). The rasied distance increased the energy loss and then
decreased the CRET efficiency. Accordingly, all subsequent CL
experiments were conducted with
C\textsubscript{8}-TPE-C\textsubscript{4}TAB.

It is reported that the pH distribution in CTAB micelle solution is not
uniform because of the adsorption of hydroxyl anions around the outside
ternary ammonium cation layer.\textsuperscript{20} Therefore, the local
pH around micelle surface is slightly higher than that in solution. As
is known, luminol could emit the strong CL under alkaline
environment.\textsuperscript{52} To understand whether the surface
adsorption hydroxyl anions affect the CL reaction, the CL signals of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}-C\textsubscript{8}-TPE-C\textsubscript{4}TAB
system without and with the introduction of NaBr or NaCl were
investigated. As shown in Figure S9, the CL intensity decreased upon
adding 1.0 mM Br\textsuperscript{-} or Cl\textsuperscript{-}. The
addition of Br\textsuperscript{-} or Cl\textsuperscript{-} would squeeze
out the adsorbed hydroxyl anions, decreasing the pH around micelle
surface and inhibiting the CL reaction. Such a result was also observed
in CTAB-modified montmorillonite improved CL system, the removal of
halide counterions of CTAB layer had a positive effect on the CL
amplification.\textsuperscript{53}

It should be noticed that the acidity of
H\textsubscript{2}O\textsubscript{2} is very weak (p\emph{K}
\textsubscript{a} \textasciitilde{}11.7), that means the molar fraction
of peroxide anion form increases with an increase in pH. However, under
pH 7.4, the molar fraction of peroxide anion form was calculated to be
5.0\selectlanguage{ngerman}×10\selectlanguage{english}\textsuperscript{-5}, suggesting most
H\textsubscript{2}O\textsubscript{2} exists as neutral molecule form.
This is why
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
only produces ultraweak CL emission. After the addition of
C\textsubscript{8}-TPE-C\textsubscript{4}TAB, the adsorbed peroxide
anions increased the local pH, which benefits the following CL reaction,
and the consumed peroxide anions would be supplied by aqueous
H\textsubscript{2}O\textsubscript{2}. The pH-dependent molar fractions
of peroxide species were calculated and listed in Table S1. In a ward,
the non-uniform pH distribution may impel the diffusion of
H\textsubscript{2}O\textsubscript{2} from solution to micelle surface.
However, the reaction rate was still slow due to the low molar fraction
of peroxide anions. Interestingly, this process endows slow CL kinetics
and long-lasting CL emission characters of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system.
On the other hand, the addition of surfactant also increased the
viscosity of solution. The increased viscosity inhibited the diffusion
of peroxide anions and limited the following CL reaction. To verify the
viscosity-mediated CL performances, the CL signals of
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
were investigated in the absence and presence of glycerol. The CL
kinetics became slow as the introduction of glycerol, as shown in Figure
S10. These results demonstrated that
C\textsubscript{8}-TPE-C\textsubscript{4}TAB-induced long-lasting CL
emission might be attributed to the increased viscosity and the
decreased fusion of reactants. Taken together,
C\textsubscript{8}-TPE-C\textsubscript{4}TAB-mediated intensive and
long-lasting CL emission is due to the synergistic effect of
micelle-improved enrichment, the diffusion control of reactants and
high-efficient CRET.

\textbf{Long-lasting performances of the proposed CL system.} To perform
the long-lasting emission more clearly, the CL images were taken in real
time by camera. For acquiring effective images, the concentrations of
luminol, Co\textsuperscript{2+}, H\textsubscript{2}O\textsubscript{2},
and C\textsubscript{8}-TPE-C\textsubscript{4}TAB were 60 \selectlanguage{greek}μ\selectlanguage{english}M, 10 nM, 2.5
mM, and 80 \selectlanguage{greek}μ\selectlanguage{english}M, respectively. The image was acquired with an interval of
4 min. Since the reaction occurs quickly, the 0 min point was not
obtained; we herein provided the 0.5 min image as the first picture. As
shown in Figure 7, bright blue emission was easily observed after the
mixing of all CL substrates. Interestingly, there was no visible light
attenuation even after 16 min reaction (Figure S11), suggesting this
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}-C\textsubscript{8}-TPE-C\textsubscript{4}TAB
system was stable. Despite of the gradually decreased emission with the
increasing reaction time, the CL emission was still observed after 60
min reaction. These results further verified the feasibility of the
enhancement of intensive and long-lasting luminol CL by adding
C\textsubscript{8}-TPE-C\textsubscript{4}TAB. The bright and
long-lasting CL emission makes the
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}-C\textsubscript{8}-TPE-C\textsubscript{4}TAB
system possible to construct a facile cold light for practical
applications.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image7/image7}

\end{center}
\end{figure}

\textbf{Figure 7.} Time-dependent image of the
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}-C\textsubscript{8}-TPE-C\textsubscript{4}TAB
system solution with 4 min interval acquisition.

\textbf{3. Conclusion}

In summary, the intensive
luminol-Co\textsuperscript{2+}-H\textsubscript{2}O\textsubscript{2}system
with long-lasting CL emission has been explored by introducing the
C\textsubscript{8}-TPE-C\textsubscript{4}TAB AIE surfactant. The
micelle-improved enrichment and diffusion control of reactants and CRET
were critical to amplify the CL signals. The visible CL emissions can be
observed even after 60 min reaction at pH 7.4. This work not only
develops a simple and glow-type luminol CL system, but also provides a
general tactic to construct the novel surfactant-mediated CL system by
introducing AIE surfactant with ultralow CMC, which reduces the usage of
surfactant and environmental pollution. Moreover, our work also provides
a deep learning of the relationship between CMC and surfactant-improved
CL signals. Therefore, we believe this strategy might benefit the
exploration of green and effective CL systems for lighting, optical
sensing and photocatalysis applications, \emph{etc} .

\textbf{Acknowledgements}

This work was supported by the National Natural Science Foundation of
China (U22A20397, 21974008 and 22074005), the Natural Science Foundation
of Beijing Municipality (2202038).

\textbf{Conflict of Interests}

The authors declare no competing financial interest.

\textbf{Supporting Information}

Supporting Information is available from the Wiley Online Library or
from the author.

Received: ((will be filled in by the editorial staff)) Revised: ((will
be filled in by the editorial staff)) Published online: ((will be filled
in by the editorial staff))

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C\textsubscript{8}-TPE-C\textsubscript{4}TAB micelle mediated intensive
and long-lasting CL of
luminol--H\textsubscript{2}O\textsubscript{2}--Co\textsuperscript{2+}system
with ultralow CMC.

\textbf{Keywords:} long-lasting chemiluminescence, fluorescent
surfactant, aggregation-induced emission,

Youkai Yu,\textsuperscript{1} Zhiqin Yuan*\textsuperscript{,2} and Chao
Lu*\textsuperscript{,1,2}

\textsuperscript{1} Y. Yu, Dr. Z. Yuan and Prof. Dr. C. Lu State Key
Laboratory of Chemical Resource Engineering, College of Chemistry,
Beijing University of Chemical Technology, Beijing 100029, China

E-mail: yuanzq@mail.buct.edu.cn (Z. Yuan), luchao@mail.buct.edu.cn (C.
Lu). Phone/Fax: +86 10 64411957.

\textsuperscript{2} Prof. Dr. C. Lu Green Catalysis Center, and College
of Chemistry, Zhengzhou University, Zhengzhou 450001, China

\textbf{Long-Lasting Chemiluminescence by Aggregation-Induced Emission
Surfactant with Ultralow Critical Micelle Concentration}\selectlanguage{english}
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\includegraphics[width=0.70\columnwidth]{figures/image8/image8}

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