The spectral properties of associates of methylene blue molecules with colloidal CdS quantum dots and
CdS / Cd(OH)2 «core-shell» systems were investigated. It is shown that according to env ironment
methylene blue changes its photophysical properties during association. These properties are due to
changes of MB structure as a result of oxidation-reduction reactions.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3527

Khoklov, V.Yu.

Latyshev, A.N.

Ovchinnikov, O.V.

Shapiro, B.I.

Shatskikh, T.S.

Smirnov, M.S.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 3, 03NCNN15(4pp) (2013)   2304-1862/2013/2(3)03NCNN15(4) 03NCNN15-1  2013 Sumy State University The Photophysical Properties Investigation of Hybrid Associates of Methylene Blue  Molecules with Colloidal CdS Quantum Dots and CdS / Cd(OH)2 "Core-Shell" Systems   T.S. Shatskikh1,*, O.V. Ovchinnikov1,†, M.S. Smirnov1, B.I. Shapiro2, A.N. Latyshev1, V.Yu. Khoklov1  1 Department of Optics and Spectroscopy, Voronezh State University, Voronezh, 394006 Voronezh,  Russian Federation 2 Lomonosov State University of Fine Chemical Technology, 119571 Moscow, Russian Federation  (Received 19 May 2013; published online 31 August 2013)  The spectral properties of associates of methylene blue molecules with colloidal CdS quantum dots and CdS / Cd(OH)2 «core-shell» systems were investigated. It is shown that according to env ironment  methylene blue changes its photophysical properties during association. These properties are due to changes of MB structure as a result of oxidation-reduction reactions.  Keywords: CdS quantum dot, Methylene blue, Hybrid associates, Luminescence.   PACS numbers: 78.55.Et, 81.07. – b, 78.67.Hc                                                           * tamara-shatskikh@rambler.ru †Ovchinnikov_O_V@rambler.ru 1. INTRODUCTION  Today various objects of nanotechnology are very interesting. Particularly, hybrid systems, composed of semiconductor quantum dots (QDs) and biologically active molecules, are interesting. It is due to large range of potential applications, including photocata-lysts, the components of photovoltaic devices, biological and medical chips, etc. [1-3]. Now, colloidal quantum dots (CdSe, CdTe, ZnSe, etc.) and their associates with molecules of porphyrins, phthalocyanines, thiazines and ect. are used as a model hybrid nanostructures for various kinds of medical and biological applications [4-6]. One of the most perspective materials for construct-ing of hybrid associates is thiazine methylene blue (MB) dye. Its properties let to use it for various applica-tions, including chemical indicators, markers and spec-tral sensitization systems for photovoltaic and photoca-talysis elements [1-3]. However, hybrid associates based on CdSe, CdTe, ZnSe QDs are very toxic. The conditions of them  organo-metallic synthesis are toxic too. Therefore they are inapplicable in vivo. They can only be used for la-boratory fluorescent diagnostics of biopsy material. One of this problem solution is to build-up of nontoxic shell on the luminescent core. On the one hand, the formation of the sell leads to a decrease of toxicity and increase of luminescence inten-sity. This is due to decrease of concentration of dan-gling bonds on the QDs interface. Those bonds are non-radiative recombination centers [7]. On the other hand, the shell blocks direct contact of dye molecules with QD. The variation of its thickness provides possibility for evidence primary mechanism of electron excitation interchange between components of associates. Howev-er, such manipulations transform the character of in-teraction thought "middleman" of associates compo-nents. Transformation of dye molecule structure is pos-sible during hybrid association. In this paper we analyzed the spectral properties of hybrid associates of methylene blue with colloidal CdS QDs, having variously composition of the interface part. In particular, we consider the situation when the conjugation of MB molecules was realized with growing and pre-formed surface CdS QDs, as well as in the con-ditions of systems of CdS / Cd(OH)2 «core-shell», ob-tained by sol-gel method in gelatin matrix [8].  2. EXPERIMENTAL SECTION  2.1 Investigated Samples  Gelatin-stabilised CdS QD samples were prepared by the sol-gel method [8]. QDs were synthesised by the double jet confluence of aqueous solutions of CdBr2 and Na2S with a gelatin solution in a reactor at a constant temperature of 40 C and a constant pH  7. An inert alkaline photographic gelatin solution (3 %) was used. Preparation of a mixture of CdS QDs with MB mol-ecule was realized in two ways [8]. In one case, aqueous solution of MB with the required concentration was introduced into the melt of the gelatin sol during the final stage of CdS QD growth. In the other case, mixing of MB molecules was produced with already formed CdS QDs. The first method provides interaction of MB molecules with growing surface of CdS QDs, and the second provides it with already formed surface. The reactivity of CdS QDs surface in these different condi-tions must have different surface composition and its donor-acceptor properties. The "core-shell" systems were obtained by build up of sell on colloidal CdS QDs, obtained by sol-gel meth-od. Detailed description of the preparation technique is given in [8]. The CdS / Cd(OH)2 shell was prepared by slow injection of aqueous solutions of NaOH and CdBr2 in gelatin sol, formed colloidal CdS QDs. The quantity of introduced reagents was calculated taking into ac-count the receipt of a two-monolayers coatings of QDs surface by shell. In this case the MB aqueous solution  T.S. SHATSKIKH, O.V. OVCHINNIKOV, M.S. SMIRNOV, ET AL. PROC. NAP 2, 03NCNN15 (2013)   03NCNN15-2 was injected into gelatin sol formed CdS / Cd(OH)2 «core-shell» systems. High purity crystal hydrates of MB, given by Sig-ma-Aldrich company were used for the preparation of MB aqueous solutions. MB was added to a 10 – 3 ÷ 10 – 2 mole of dye / mole of CdS QDs concentrations (mol fraction or m.f.). At maximal concentrations of MB 4 molecules of the dye fit one QD had a diameter of 2.5-2.7 nm. The preparing mixture was applied to a quartz plate. The identification of colloidal CdS QDs was made using a transmission electron microscope (TEM) LEO ~ 912AB ~ OMEGA. Analysis of the electron micro-graphs shows that isolated CdS nanoparticles with average size of 2.5 nm are formed. When core of CdS QDs was covered by shell with thickness of up to two monolayers we observed an increase in the average size. It is about 1.2 nm. The reverse electron scattering analysis showed that the crystallization of CdS QDs are in a cubic lattice.  2.2 Methods of Investigations and Equipment   The investigations were performed with the use of luminescence and absorption techniques. The absorp-tion and luminescence spectra of prepared samples were investigated using the absorption spectrophotometer Shimadzu UV 2501 (Japan) and fully automatic spec-tral-luminescent complex. This complex was built on the basis of the diffraction monochromator and photo-multiplier (R928P Hamamatsu, Japan, battery energy source C4900-51), operating in the photon counting mode. Luminescence of samples was excited by UV ra-diation produced by an HPL-H77GV1BT-V1 diode  module (max  380 nm, Pmax  5 mW). The presented results were obtained at room temperature.  3. RESULTS AND DISCUSSION  Fig. 1 shows the normalized absorption spectra of MB in variously environment. The following main regularities were identified in these spectra:    Fig. 1 – Normalized absorption spectra of MB (10-2 m.f.) in variously environment. 1 – mixture with CdS QDs (conjugation with growing QD surface); 2 – mixture with CdS QDs (conjugation with formed QD surface); 3 – mixture with CdS / Cd(OH)2 (1 monolayer); 4 – mixture with CdS / Cd(OH)2 (3 monolayer)  • For MB, conjugated with the growing surface of col-loidal CdS QDs maximum absorption is hypsochromical-ly shifted with respect to the main peak of MB spectrum in gelatin (max  664 nm) to 10 nm (Fig. 1(1)). • The absorption spectrum of MB molecules, conju-gated with formed surface of CdS QDs has band at max1  664 nm and max2  613 nm and feature at 570-580 nm (Fig. 1(2)). This spectrum is close to the spec-trum of MB in the gelatin. • The absorption spectrum of a mixture of MB mole-cules with CdS / Cd(OH)2 QDs, having the shell thick-ness no more than a monolayer, has a pronounced max-imum at max1  670 nm (Fig. 1(3)) and the feature at the absorption band of MB dimers (610-615 nm). When Cd(OH)2 sell thickness is increase to 2-3 monolayers there is another band with max3  565 nm (Fig. 1(4)). The absorption band intensity of the monomers and di-mers of MB is decreases. Luminescent properties of hybrid associates of CdS QDs and Cd(OH)2 «core-sell» systems with MB molecules in the gelatin were investigated using excitation radia-tion with wavelengths ex  380 nm. It occurs in the re-gion of excitation emission of QDs. In photoluminescence spectra excited by ex  380 nm, it was found that the CdS QDs fluoresce is brightly enough. Maximum of luminescence is located at 540-550 nm (Fig. 2(1)). In the presence of MB molecules luminescent proper-ties of CdS QDs are undergoing significant changes. The luminescence band was recorded in the long-wavelength part of the spectrum. Its maximum for mixtures of MB molecules with growing surface of colloidal CdS QDs is located at 681 nm (Fig. 2(1)). In the case of formed QDs surface long-wavelength maximum of luminescence was located at 674 nm (Fig. 2(1'')). Moreover, for all types of associations we had the same pattern. It is the lumines-cence quenching in the QD band and a significant in-crease in the fluorescence of MB in the region of 674 ÷ 684 nm.    Fig. 2 – Luminescence spectra of QDs and hybrid associates with MB (10-2 m.f.). 1 – CdS QDs; 1’ – mixture with CdS QDs (conjugation with growing QD surface); 1’’ – mixture with CdS QDs (conjugation with formed QD surface); 2 – CdS / Cd(OH)2 (3 monolayer); 2’ – mixture with CdS / Cd(OH)2 (3 monolayer)  For "core-shell" systems the maximum of lumines-cence spectrum is shifted to longer wavelengths range as compared with QDs without sell (Fig. 2 (2, 3)). When MB  THE PHOTOPHYSICAL PROPERTIES... PROC. NAP 2, 03NCNN15 (2013)   03NCNN15-3 molecules were conjugated with CdS / Cd(OH)2 «core-shell» (2-3 monolayer) the noticeable deformation of the luminescence band and minor dip in the region 560-600 nm were detected (Fig. 2(2)). This region corre-sponds to absorption range of the dye conjugated with the CdS / Cd(OH)2 "core-shell». In the luminescence spec-trum maxima at 610 nm and 697 nm were shown up. First of all the resulting spectral features indicate the manifestation of general regularities. It is interac-tion and formation of every hybrid associates of QDs with MB molecules. The environmental conditions influ-ence significant on the spectral properties of associates. Namely it is the state of surface. The observed regularities can be explained by com-plex structures of MB molecules, which is characterized by a variety protolytic equilibrium. The neutral leuco-form MBH0 occurs as a result of the reaction MB+ + 2e + H+ → MBH0 in the presence of ions of varia-ble valence metals at pH  2  7 [9]. It is clear in the visible and near IR regions [9]. MBH2 + occurs in strong-ly acidic environments (pH  0.1) [10]. The protonated dication MBH2 + has a complex absorption band (1  741-745 nm, 2  678 nm and (3)shoulder  615 nm) [11]. Today there isn’t clear concept of what happens with MB molecule in a strongly alkaline environment. The cation MB+ accepts an electron in strongly alkaline environments (pH  11). Additionally, the neutral sem-iquinone (radical) MB0 is observed under these condi-tions. This form is interesting because it has an extend-ed absorption spectrum with five peaks in the visible region (1  420 nm, 2  436 nm, 3  585 nm, 4  610 nm, 5  640 nm) [11, 12]. At the same time, the protonated form of MB + have a band with maximum located at 510-550 nm in different solvents [12]. This form is stable to external influence. According to [13], in strongly alkaline environment there is absorption of light at 560-575 nm by hydroxide form of methylene blue [MB] OH–. In addition, there is another point of view. The dye is not simply goes over to the other form, and methylene violet dye forms [14]. The transformation into a new dye does not occur immediately. In process of time under light the transformation occurs with the possible formation of intermediate dye (Azure A, Azure B, Azure C). Transformation into methylene violet is occurred by demitiloaminogroups hydrolysis. The wide band in the region of 470-580 nm is observed [14]. The following conclusions were made considering above: 1. In the case of growing surface of CdS QDs associ-ates with cation-radical MB + are formed. The nature of the interaction is such that it prevents to form dimers [MV +]2 and H-aggregates. Hypsochromically shifted to 630-655 nm absorption band may belong to this form. The nature of hypsochromicall shift in the electronic band is caused by a change in the chain length of π-conjugation. It is due to the dimensional deformation of molecules interacting with the surface, which has a spherical curvature. 2. It was found spectrally that the structure of MB molecule is transformed during conjugation with a CdS / Cd(OH)2 system. Transformation can take place in two ways. The first way is the formation of MB-OH• structure during conjugation with CdS / Cd(OH)2 [13]. Second is the formation of a methylene violet dye [14]. When Cd(OH)2 shell is build up there are an excessive amount of OH-ions on the surface. The interaction of OH group with the nitrogen atom in heterocycle leads to  N-hydroxistructure formation of MB [15]. Non-reversible changes in methylene violet are possible during the transfer of electron to environment [16]. 3. For mixtures MB with formed surface of CDS QDs we observed absorption at max1  maxima at 664 nm and max2  613 nm, and the feature at 570 nm. Transfor-mation of this feature in separate band during increas-ing thickness of the shell to 2-3 monolayers suggests that this feature is due to the formation of same dye forms as in the case of Cd(OH)2 shell. The hydrolysis of dangling bonds is possible for formed CdS QDs surface. As its result pH of sol is shifted to alkali. Thereby, simi-lar situations as for CdS / Cd(OH)2 «core-shell » are pos-sible during adsorption of MB on surface. Definitely to say what is a degradation product of MB for these cases is not possible. Both schemes are possible. Interaction with highly reactive QDs surface can plays decisive role in the formation of associates of MB with formed surface of CdS QDs and CdS / Cd(OH)2. 4. Analysis of luminescence spectra of hybrid associ-ates of MB shows that for them the change in shape of luminescence spectrum is situated in agreement with the changes observed in absorption spectra. Principal detected feature is the increase of luminescence intensi-ty of MB and its decrease for QDs. Comparison of lumi-nescence spectra of CdS QDs and CdS / Cd(OH)2 systems with MB absorption indicates that they significantly overlap. This can be regarded as the spectral corre-spondence of resonance conditions for the transfer of electron excitation energy from CdS QDs to MB.  4. CONCLUSION  Thus, MB exhibits different spectral properties in associate. Its properties are dependence from the envi-ronment. In hybrid associates of MB with CdS QDs in the case of growing surface dye is present mainly as MB +. In hybrid associates of MB with CdS QDs in con-ditions of formed surface and CdS / Cd(OH)2 systems the conjugation is due to interaction of the dye with the interface part of QDs. It is determined by charged sur-face, presence of gelatin and hydrolysis of the dangling bonds on the surface of CdS QDs. The hydrolysis pro-vides the formation of new dye forms. They are MB0OH and methylene violet. Transformation forms of meth-ylene blue in the studied hybrid associates fully ex-plains their spectral luminescent properties.  AKNOWLEDGEMENTS  The work was supported by RFBR (project №11-02-00698-a), by the Ministry of education and science of Russian Federation (project 14.В37.21.0457).     T.S. SHATSKIKH, O.V. OVCHINNIKOV, M.S. SMIRNOV, ET AL. PROC. NAP 2, 03NCNN15 (2013)   03NCNN15-4 REFERENCES  1. K.R. Choudhury, F. So, Z. Kafafi, Comprehensive Nanosci. Techn. 193, 407 (2011). 2. A. Rakovich, D. Savateeva, T. Rakovich, J.F. Donegan, Y.P. Rakovich, V. Kelly, V. Lesnyak, A. Eychmuller, Na-noscale Res. Lett. 753, 5 (2010). 3. M. Asha Jhonsi, A. Kathiravan, R. Renganathan, J. Mol. Struc. 279, 921 (2009).  4. W.J. Parak, D. Gerion, T. Pellegrino, D. Zanchet, C. Micheel, S.C. Williams, Nanotechnology 15, 14 (2003).  5. K.Y. Kim, Nanomedicine: Nanotechnology, Biology, and Medicine, 103, 3 (2) (2007). 6. M.V. Yezhelyev, A. Al-Hajj, C. Morris, A. I. Marcus, T. Liu, M. Lewis, C. Cohen, P. Zrazhevskiy, J. W. Simons, A. Rogatko, S. Nie, X. Gao, R. M. O'Regan, Adv. Mater. 3146, 19 (2007). 7. P. Reiss, M. Protiere, L. Li, Small 154, 5 (2009).  8. O.V. Ovchinnikov, M.S. Smirnov, B.I. Shapiro, A.N. Latyshev, T.S. Shatskikh, E.E. Borduza, S.A. Soldatenko, Theor. Experym. Chem. 43, 48 (2012).  9. P.V. Kamat, N.N. Lichtin, J. Phys. Chem. 814, 85 (1981). 10. S.K. Lee, A. Mills, J. Fluorescence 375, 13 (2003). 11. S. Granick, L. Michaelis, M. Schubert, J. Phys. Chem. 1802, 62 (1940). 12. E. Braswell, J. Phys. Chem. 2483, 72 (1968). 13. K. Bergmann, C.T. O'Konski, J. Phys. Chem. 2169, 67 (1963). 14. L. Adamcikova, K. Pavlikova, P. Sevcik, React. Kinet. Catal. Lett. 91, 69 (2000). 15. S. Basu, S. Panigrahi, S. Praharaj, S.K. Ghosh, S. Pande, S. Jana, A. Pal, T. Pal, J. Phys. Chem. A 578, 111 (2007). 16. M. John Plater, Arkivoc. 37, 1 (2003).  

The Photophysical Properties Investigation of Hybrid Associates of Methylene Blue Molecules with Colloidal CdS Quantum Dots and CdS / Cd(OH)2 "Core-Shell" Systems

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 2 No 3, 03NCNN15(4pp) (2013) 
 
 
2304-1862/2013/2(3)03NCNN15(4) 03NCNN15-1  2013 Sumy State University 
The Photophysical Properties Investigation of Hybrid Associates of Methylene Blue  
Molecules with Colloidal CdS Quantum Dots and CdS / Cd(OH)2 "Core-Shell" Systems  
 
T.S. Shatskikh1,*, O.V. Ovchinnikov1,†, M.S. Smirnov1, B.I. Shapiro2, A.N. Latyshev1, 
V.Yu. Khoklov1 
 
1 Department of Optics and Spectroscopy, Voronezh State University, Voronezh, 394006 Voronezh,  
Russian Federation 
2 Lomonosov State University of Fine Chemical Technology, 119571 Moscow, Russian Federation 
 
(Received 19 May 2013; published online 31 August 2013) 
 
The spectral properties of associates of methylene blue molecules with colloidal CdS quantum dots and 
CdS / Cd(OH)2 «core-shell» systems were investigated. It is shown that according to env ironment  
methylene blue changes its photophysical properties during association. These properties are due to 
changes of MB structure as a result of oxidation-reduction reactions. 
 
Keywords: CdS quantum dot, Methylene blue, Hybrid associates, Luminescence. 
 
 PACS numbers: 78.55.Et, 81.07. – b, 78.67.Hc 
 
 
                                                        
* tamara-shatskikh@rambler.ru 
†Ovchinnikov_O_V@rambler.ru 
1. INTRODUCTION 
 
Today various objects of nanotechnology are very 
interesting. Particularly, hybrid systems, composed of 
semiconductor quantum dots (QDs) and biologically 
active molecules, are interesting. It is due to large 
range of potential applications, including photocata-
lysts, the components of photovoltaic devices, biological 
and medical chips, etc. [1-3]. 
Now, colloidal quantum dots (CdSe, CdTe, ZnSe, 
etc.) and their associates with molecules of porphyrins, 
phthalocyanines, thiazines and ect. are used as a model 
hybrid nanostructures for various kinds of medical and 
biological applications [4-6]. 
One of the most perspective materials for construct-
ing of hybrid associates is thiazine methylene blue 
(MB) dye. Its properties let to use it for various applica-
tions, including chemical indicators, markers and spec-
tral sensitization systems for photovoltaic and photoca-
talysis elements [1-3]. 
However, hybrid associates based on CdSe, CdTe, 
ZnSe QDs are very toxic. The conditions of them  
organo-metallic synthesis are toxic too. Therefore they 
are inapplicable in vivo. They can only be used for la-
boratory fluorescent diagnostics of biopsy material. 
One of this problem solution is to build-up of nontoxic 
shell on the luminescent core. 
On the one hand, the formation of the sell leads to a 
decrease of toxicity and increase of luminescence inten-
sity. This is due to decrease of concentration of dan-
gling bonds on the QDs interface. Those bonds are non-
radiative recombination centers [7]. On the other hand, 
the shell blocks direct contact of dye molecules with 
QD. The variation of its thickness provides possibility 
for evidence primary mechanism of electron excitation 
interchange between components of associates. Howev-
er, such manipulations transform the character of in-
teraction thought "middleman" of associates compo-
nents. Transformation of dye molecule structure is pos-
sible during hybrid association. 
In this paper we analyzed the spectral properties of 
hybrid associates of methylene blue with colloidal CdS 
QDs, having variously composition of the interface 
part. In particular, we consider the situation when the 
conjugation of MB molecules was realized with growing 
and pre-formed surface CdS QDs, as well as in the con-
ditions of systems of CdS / Cd(OH)2 «core-shell», ob-
tained by sol-gel method in gelatin matrix [8]. 
 
2. EXPERIMENTAL SECTION 
 
2.1 Investigated Samples 
 
Gelatin-stabilised CdS QD samples were prepared 
by the sol-gel method [8]. QDs were synthesised by the 
double jet confluence of aqueous solutions of CdBr2 and 
Na2S with a gelatin solution in a reactor at a constant 
temperature of 40 C and a constant pH  7. An inert 
alkaline photographic gelatin solution (3 %) was used. 
Preparation of a mixture of CdS QDs with MB mol-
ecule was realized in two ways [8]. In one case, aqueous 
solution of MB with the required concentration was 
introduced into the melt of the gelatin sol during the 
final stage of CdS QD growth. In the other case, mixing 
of MB molecules was produced with already formed 
CdS QDs. The first method provides interaction of MB 
molecules with growing surface of CdS QDs, and the 
second provides it with already formed surface. The 
reactivity of CdS QDs surface in these different condi-
tions must have different surface composition and its 
donor-acceptor properties. 
The "core-shell" systems were obtained by build up 
of sell on colloidal CdS QDs, obtained by sol-gel meth-
od. Detailed description of the preparation technique is 
given in [8]. The CdS / Cd(OH)2 shell was prepared by 
slow injection of aqueous solutions of NaOH and CdBr2 
in gelatin sol, formed colloidal CdS QDs. The quantity 
of introduced reagents was calculated taking into ac-
count the receipt of a two-monolayers coatings of QDs 
surface by shell. In this case the MB aqueous solution 
 T.S. SHATSKIKH, O.V. OVCHINNIKOV, M.S. SMIRNOV, ET AL. PROC. NAP 2, 03NCNN15 (2013) 
 
 
03NCNN15-2 
was injected into gelatin sol formed CdS / Cd(OH)2 
«core-shell» systems. 
High purity crystal hydrates of MB, given by Sig-
ma-Aldrich company were used for the preparation of 
MB aqueous solutions. MB was added to a 10 – 3 ÷ 10 –
 2 mole of dye / mole of CdS QDs concentrations (mol 
fraction or m.f.). At maximal concentrations of MB 
4 molecules of the dye fit one QD had a diameter of 2.5-
2.7 nm. The preparing mixture was applied to a quartz 
plate. 
The identification of colloidal CdS QDs was made 
using a transmission electron microscope (TEM) LEO 
~ 912AB ~ OMEGA. Analysis of the electron micro-
graphs shows that isolated CdS nanoparticles with 
average size of 2.5 nm are formed. When core of CdS 
QDs was covered by shell with thickness of up to two 
monolayers we observed an increase in the average 
size. It is about 1.2 nm. The reverse electron scattering 
analysis showed that the crystallization of CdS QDs 
are in a cubic lattice. 
 
2.2 Methods of Investigations and Equipment  
 
The investigations were performed with the use of 
luminescence and absorption techniques. The absorp-
tion and luminescence spectra of prepared samples were 
investigated using the absorption spectrophotometer 
Shimadzu UV 2501 (Japan) and fully automatic spec-
tral-luminescent complex. This complex was built on the 
basis of the diffraction monochromator and photo-
multiplier (R928P Hamamatsu, Japan, battery energy 
source C4900-51), operating in the photon counting 
mode. Luminescence of samples was excited by UV ra-
diation produced by an HPL-H77GV1BT-V1 diode  
module (max  380 nm, Pmax  5 mW). The presented 
results were obtained at room temperature. 
 
3. RESULTS AND DISCUSSION 
 
Fig. 1 shows the normalized absorption spectra of 
MB in variously environment. 
The following main regularities were identified in 
these spectra: 
 
 
 
Fig. 1 – Normalized absorption spectra of MB (10-2 m.f.) in 
variously environment. 1 – mixture with CdS QDs 
(conjugation with growing QD surface); 2 – mixture with CdS 
QDs (conjugation with formed QD surface); 3 – mixture with 
CdS / Cd(OH)2 (1 monolayer); 4 – mixture with CdS / Cd(OH)2 
(3 monolayer) 
 
• For MB, conjugated with the growing surface of col-
loidal CdS QDs maximum absorption is hypsochromical-
ly shifted with respect to the main peak of MB spectrum 
in gelatin (max  664 nm) to 10 nm (Fig. 1(1)). 
• The absorption spectrum of MB molecules, conju-
gated with formed surface of CdS QDs has band at 
max1  664 nm and max2  613 nm and feature at 570-
580 nm (Fig. 1(2)). This spectrum is close to the spec-
trum of MB in the gelatin. 
• The absorption spectrum of a mixture of MB mole-
cules with CdS / Cd(OH)2 QDs, having the shell thick-
ness no more than a monolayer, has a pronounced max-
imum at max1  670 nm (Fig. 1(3)) and the feature at the 
absorption band of MB dimers (610-615 nm). When 
Cd(OH)2 sell thickness is increase to 2-3 monolayers 
there is another band with max3  565 nm (Fig. 1(4)). 
The absorption band intensity of the monomers and di-
mers of MB is decreases. 
Luminescent properties of hybrid associates of CdS 
QDs and Cd(OH)2 «core-sell» systems with MB molecules 
in the gelatin were investigated using excitation radia-
tion with wavelengths ex  380 nm. It occurs in the re-
gion of excitation emission of QDs. 
In photoluminescence spectra excited by 
ex  380 nm, it was found that the CdS QDs fluoresce is 
brightly enough. Maximum of luminescence is located at 
540-550 nm (Fig. 2(1)). 
In the presence of MB molecules luminescent proper-
ties of CdS QDs are undergoing significant changes. The 
luminescence band was recorded in the long-wavelength 
part of the spectrum. Its maximum for mixtures of MB 
molecules with growing surface of colloidal CdS QDs is 
located at 681 nm (Fig. 2(1)). In the case of formed QDs 
surface long-wavelength maximum of luminescence was 
located at 674 nm (Fig. 2(1'')). Moreover, for all types of 
associations we had the same pattern. It is the lumines-
cence quenching in the QD band and a significant in-
crease in the fluorescence of MB in the region of 
674 ÷ 684 nm. 
 
 
 
Fig. 2 – Luminescence spectra of QDs and hybrid associates 
with MB (10-2 m.f.). 1 – CdS QDs; 1’ – mixture with CdS QDs 
(conjugation with growing QD surface); 1’’ – mixture with CdS 
QDs (conjugation with formed QD surface); 2 – CdS / Cd(OH)2 
(3 monolayer); 2’ – mixture with CdS / Cd(OH)2 (3 monolayer) 
 
For "core-shell" systems the maximum of lumines-
cence spectrum is shifted to longer wavelengths range as 
compared with QDs without sell (Fig. 2 (2, 3)). When MB 
 THE PHOTOPHYSICAL PROPERTIES... PROC. NAP 2, 03NCNN15 (2013) 
 
 
03NCNN15-3 
molecules were conjugated with CdS / Cd(OH)2 «core-
shell» (2-3 monolayer) the noticeable deformation of the 
luminescence band and minor dip in the region 560-
600 nm were detected (Fig. 2(2)). This region corre-
sponds to absorption range of the dye conjugated with 
the CdS / Cd(OH)2 "core-shell». In the luminescence spec-
trum maxima at 610 nm and 697 nm were shown up. 
First of all the resulting spectral features indicate 
the manifestation of general regularities. It is interac-
tion and formation of every hybrid associates of QDs 
with MB molecules. The environmental conditions influ-
ence significant on the spectral properties of associates. 
Namely it is the state of surface. 
The observed regularities can be explained by com-
plex structures of MB molecules, which is characterized 
by a variety protolytic equilibrium. The neutral leuco-
form MBH0 occurs as a result of the reaction 
MB+ + 2e + H+ → MBH0 in the presence of ions of varia-
ble valence metals at pH  2  7 [9]. It is clear in the 
visible and near IR regions [9]. MBH2 + occurs in strong-
ly acidic environments (pH  0.1) [10]. The protonated 
dication MBH2 + has a complex absorption band 
(1  741-745 nm, 2  678 nm and (3)shoulder  615 nm) 
[11]. Today there isn’t clear concept of what happens 
with MB molecule in a strongly alkaline environment. 
The cation MB+ accepts an electron in strongly alkaline 
environments (pH  11). Additionally, the neutral sem-
iquinone (radical) MB0 is observed under these condi-
tions. This form is interesting because it has an extend-
ed absorption spectrum with five peaks in the visible 
region (1  420 nm, 2  436 nm, 3  585 nm, 
4  610 nm, 5  640 nm) [11, 12]. At the same time, the 
protonated form of MB + have a band with maximum 
located at 510-550 nm in different solvents [12]. This 
form is stable to external influence. According to [13], in 
strongly alkaline environment there is absorption of 
light at 560-575 nm by hydroxide form of methylene blue 
[MB] OH–. In addition, there is another point of view. 
The dye is not simply goes over to the other form, and 
methylene violet dye forms [14]. The transformation into 
a new dye does not occur immediately. In process of time 
under light the transformation occurs with the possible 
formation of intermediate dye (Azure A, Azure B, Azure 
C). Transformation into methylene violet is occurred by 
demitiloaminogroups hydrolysis. The wide band in the 
region of 470-580 nm is observed [14]. 
The following conclusions were made considering 
above: 
1. In the case of growing surface of CdS QDs associ-
ates with cation-radical MB + are formed. The nature of 
the interaction is such that it prevents to form dimers 
[MV +]2 and H-aggregates. Hypsochromically shifted to 
630-655 nm absorption band may belong to this form. 
The nature of hypsochromicall shift in the electronic 
band is caused by a change in the chain length of π-
conjugation. It is due to the dimensional deformation of 
molecules interacting with the surface, which has a 
spherical curvature. 
2. It was found spectrally that the structure of MB 
molecule is transformed during conjugation with a 
CdS / Cd(OH)2 system. Transformation can take place in 
two ways. The first way is the formation of MB-OH• 
structure during conjugation with CdS / Cd(OH)2 [13]. 
Second is the formation of a methylene violet dye [14]. 
When Cd(OH)2 shell is build up there are an excessive 
amount of OH-ions on the surface. The interaction of OH 
group with the nitrogen atom in heterocycle leads to  
N-hydroxistructure formation of MB [15]. Non-reversible 
changes in methylene violet are possible during the 
transfer of electron to environment [16]. 
3. For mixtures MB with formed surface of CDS QDs 
we observed absorption at max1  maxima at 664 nm and 
max2  613 nm, and the feature at 570 nm. Transfor-
mation of this feature in separate band during increas-
ing thickness of the shell to 2-3 monolayers suggests 
that this feature is due to the formation of same dye 
forms as in the case of Cd(OH)2 shell. The hydrolysis of 
dangling bonds is possible for formed CdS QDs surface. 
As its result pH of sol is shifted to alkali. Thereby, simi-
lar situations as for CdS / Cd(OH)2 «core-shell » are pos-
sible during adsorption of MB on surface. Definitely to 
say what is a degradation product of MB for these cases 
is not possible. Both schemes are possible. Interaction 
with highly reactive QDs surface can plays decisive role 
in the formation of associates of MB with formed surface 
of CdS QDs and CdS / Cd(OH)2. 
4. Analysis of luminescence spectra of hybrid associ-
ates of MB shows that for them the change in shape of 
luminescence spectrum is situated in agreement with 
the changes observed in absorption spectra. Principal 
detected feature is the increase of luminescence intensi-
ty of MB and its decrease for QDs. Comparison of lumi-
nescence spectra of CdS QDs and CdS / Cd(OH)2 systems 
with MB absorption indicates that they significantly 
overlap. This can be regarded as the spectral corre-
spondence of resonance conditions for the transfer of 
electron excitation energy from CdS QDs to MB. 
 
4. CONCLUSION 
 
Thus, MB exhibits different spectral properties in 
associate. Its properties are dependence from the envi-
ronment. In hybrid associates of MB with CdS QDs in 
the case of growing surface dye is present mainly as 
MB +. In hybrid associates of MB with CdS QDs in con-
ditions of formed surface and CdS / Cd(OH)2 systems 
the conjugation is due to interaction of the dye with the 
interface part of QDs. It is determined by charged sur-
face, presence of gelatin and hydrolysis of the dangling 
bonds on the surface of CdS QDs. The hydrolysis pro-
vides the formation of new dye forms. They are MB0OH 
and methylene violet. Transformation forms of meth-
ylene blue in the studied hybrid associates fully ex-
plains their spectral luminescent properties. 
 
AKNOWLEDGEMENTS 
 
The work was supported by RFBR (project №11-02-
00698-a), by the Ministry of education and science of 
Russian Federation (project 14.В37.21.0457). 
 
 
 
 T.S. SHATSKIKH, O.V. OVCHINNIKOV, M.S. SMIRNOV, ET AL. PROC. NAP 2, 03NCNN15 (2013) 
 
 
03NCNN15-4 
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The Photophysical Properties Investigation of Hybrid Associates of Methylene Blue Molecules with Colloidal CdS Quantum Dots and CdS / Cd(OH)2 "Core-Shell" Systems

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