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Novel nanomaterials based on 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)21H,23H-porphyrin entrapped in silica matrices Eugenia Fagadar-Cosma a,*, Corina Enache a, Dana Vlascici b, Gheorghe Fagadar-Cosma c, Mihaela Vasile d, Grzegorz Bazylak e a
Institute of Chemistry Timisoara of Romanian Academy, M. Viteazu Ave, No. 24, 300223 Timisoara, Romania West University of Timisoara, Pestalozzi Street, No. 16, 300115 Timisoara, Romania ‘‘Politehnica’’ University, T. Lalescu Street, No. 2, 300223 Timisoara, Romania d National Institute for Research and Development in Electrochemistry and Condensed Matter, P. Andronescu Street, No. 1, 300224 Timisoara, Romania e Collegium Medicum, Nicolaus Copernicus University, Department of Pharmaco-Bromatology & Molecular Nutrition, Jagiellonska, No. 13, PL-85-067 Bydgoszcz, Poland b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 29 December 2008 Received in revised form 19 July 2009 Accepted 12 August 2009 Available online xxx
The present study is dealing with the obtaining of transparent hybrid silica materials encapsulating 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)-21H,23H-porphyrin designated for advanced optoelectronic devices. The porphyrin was synthesized by three methods: an Adler-type reaction between pyrrole and 3,4-dimethoxybenzaldehyde in propionic acid medium; by Lindsey condensation of pyrrole with 3,4dimethoxybenzaldehyde in the presence of BF3OEt2 and by a multicomponent reaction by simultaneously using of pyrrole and two different aldehydes: 3,4-dimethoxybenzaldehyde and 3hydroxybenzaldehyde. The 3,4-dimethoxyphenyl substituted porphyrin was characterized by HPLC, TLC, UV–vis, FT-IR, 1H NMR and 13C NMR analysis. Excitation and emission spectra were also discussed in terms of pH conditions. The hybrid materials, consisting in the porphyrin encapsulated in silica matrices, have been prepared successfully via the two steps acid–base catalyzed hydrolysis and condensation of tetraethylorthosilicate using different approaches of the sol–gel process: in situ, by impregnation and by sonication. The synthetic conditions and the compositions were monitored and characterized by using spectroscopic methods such as FT-IR, fluorescence and UV–vis. Atomic force microscopy (AFM) has been applied to observe the columnar or pyramidal nanostructures which are formed by the immobilization of porphyrin on the silica matrices. ß 2009 Elsevier Ltd. All rights reserved.
Keywords: A. nanostructures A. organic compounds B. sol-gel chemistry C. atomic force microscopy D. luminescence
1. Introduction Sol–gel processing [1–5] can be used to synthesize nanostructured ceramic powders, glasses, fibers and films. During a sol– gel process, the most important factors that need to be taken into consideration are the nature of precursors, catalysts, solvent, pH, temperature, stirring conditions and the type of additives. The pH affects strongly the hydrolysis and condensation reactions of a sol–gel process. Hydrolysis reactions are favored by acid media, which means that all or almost all hydrolyzed species are formed before condensation begins. Under acidic conditions there is a low crosslink density, which yields a denser final product when the gel collapses. Instead, condensation reactions are favored by basic conditions, therefore, condensation begins before hydrolysis is complete. The pH level also affects the isoelectric point and the stability of the sol and as a consequence
* Corresponding author. Tel.: +40 256 491818; fax: +40 256 491824. E-mail address:
[email protected] (E. Fagadar-Cosma).
the type of aggregation and particle size, so that the structure, topography and properties of the gel can be predicted [6]. Ceramic nanomaterials based on silica [7] are known for their stability and compatibility in biological systems [8], and their synthesis has been extensively reported in the last decades for their promising application in drug delivery and in formulation of sensor devices [9] and efficient catalytic systems for photo-oxidation [10]. Because of their highly conjugated p-electron system, porphyrin derivatives are considered promising structures for developing two-photon absorption (2PA) materials [11]. Ceramic-based materials entrapping porphyrins [12,13] exhibiting a non-linear optical phenomenon might find various optical applications especially in photodynamic therapy [14–17]. Hydrated ceramic-based nanoparticles, doped with photosensitive drugs, carry the promise of solving many of the problems associated with free as well as polymer-encapsulated drugs. State of the art strategies have evolved to find a carrier, to enable a stable dispersion of these photosensitizing drugs, which are mostly hydrophobic, into aqueous systems, in order to become proper for parenteral administration [18].
0025-5408/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2009.08.010
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Besides, porphyrins used as photosensitizers are suitable for efficient electron transfer with small reorganization energies. Extensive absorption characteristics of porphyrin systems guarantee increased absorption cross-sections and an efficient use of the solar spectrum, making them excellent candidates for use in design of photovoltaic devices [19–22]. Porphyrins embedded in sol–gel ceramic films and silica glasses are also used in various sensor devices for clinical analysis for dopamine, uric acid and oxygen detection [23–25] and obtained in a form of particles spherical and monodispersed showed to be promising catalytic systems for selective oxidation [26] or acting as biomimetic catalysts [27]. The field of synthetic porphyrin chemistry is a spectacular area of research, especially because of the aim to design porphyrin building blocks able to compete in performance with natural systems. Based on the potential applications of these compounds, their synthesis was done both by preparation of compounds where functionality is introduced during the formation of the porphyrin ring or by functionalization of the preformed porphyrin macrocycle. The first synthetic symmetrical meso-porphyrin was prepared by Rothmund in 1936 [28]. His method was improved by Adler– Longo [29–31], and ulterior the method developed by Lindsey offered a crucial extent [32–34]. Some drawbacks of Adler–Longo method are the formation of the reduced porphyrin (chlorin) which contaminates the product and of polypyrrolic products, this going to a small yield of the desired product. A second problem is that the reaction could not undergo with aldehydes containing acid sensitive functional groups [35]. The advantage of Lindsey method, which is based on the formation of porphyrinogen as an intermediate in porphyrin synthesis, is that it allows the formation of porphyrins from sensitive aldehydes, in higher yields, with more facile purification [36]. The asymmetrical porphyrins are much more difficult to synthesize. Their preparation is based on various approaches of Adler–Longo conditions, Lindsey method, 2 + 2 porphyrin [37,38] and 3 + 1 porphyrin syntheses [39,40], or by synthesis of porphyrins from linear tetrapyrrols [41]. The present work is dealing with the synthesis of novel hybrid porphyrin–silica nanomaterials, by controlled sol–gel process. These materials are characterized by surfaces with particles of low size, controlled shape, and high porosity, and are extremely stable. The hybrid materials, consisting in 5,10,15,20-tetrakis(3,4dimethoxyphenyl)-21H,23H-porphyrin (TDMPP) (Fig. 1) encapsulated in silica matrices, have been prepared successfully via the two steps acid–base catalyzed hydrolysis and condensation of tetraethylorthosilicate using different approaches of the sol–gel process: in situ, by impregnation and by sonication. The synthetic conditions and the compositions were monitored and characterized by using spectroscopic methods such as FT-IR, fluorescence and UV–vis. Atomic force microscopy (AFM) has been applied to observe the columnar or pyramidal nanostructures which are formed by the immobilization of porphyrin (TDMPP) on the silica matrices. Starting from the consideration that in case of the porphyrins free base incorporated in amorphous inorganic solids the mechanism of PHB is light-induced tautomerization of the pair of central protons in molecule and having scientific interest regarding the possibility of the application to high-density optical data storage, this study was done only in acid–base catalysis, because in acidic solutions, many porphyrins change their forms into dication that is inactive in photochemical hole-burning (PHB) [42,43].
Fig. 1. The structure of 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)porphyrin (TDMPP).
2. Experimental detail 2.1. Chemicals The porphyrin (TDMPP) was synthesized by three different ways: an Adler-type reaction between pyrrole and 3,4-dimethoxybenzaldehyde in propionic acid medium, followed by purification by silica gel column chromatography using as eluent chloroform/ ethylic ether mixture of ratio 5/1 [29]; by Lindsey condensation of pyrrole with 3,5-dimethoxy-benzaldehyde in the presence of BF3OEt2 [32] and by a multicomponent reaction, as previously fully characterized and reported [44]. Reagents were p.a. grade and were purchased from Fluka, Aldrich and Merck and used as received, excepting pyrrole distilled prior to use. Chloroform was stored over 4 A˚ molecular sieves. CH2Cl2 was distilled from CaH2 under nitrogen. Tetraethyl orthosilicate (TEOS, 98%, Fluka), tetrahydrofuran (THF, 98%, Merck), ethanol absolute (EtOH, Chemopar) were all used without further purification. Thin-layer chromatography (TLC) was performed on 25 DCAlufolien Aluminiumoxid 60 F254 Neutral (Merck). Solvent systems associated with Rf values and chromatography data are reported as v/v ratios. Column Chromatography was performed at room temperature with silica gel 60 (230–400 mesh, 0.040–0.063 mm), purchased from Merck. 2.2. Sol–gel preparations 2.2.1. In situ two steps acid/base catalyzed sol–gel method starting fromTEOS A mixture of H2O and HCl 37% was added by slow dripping under vigorous stirring to a solution of TEOS dissolved into EtOH. The following molar ratios were kept constant during the first acidic step: TEOS:EtOH:H2O:HCl = 1:4:4:0.02. After 15 min, the second basic step was started by slowly adding of NH3 2.5%. At the moment when viscosity has been increased, a solution of porphyrin (TDMPP) in THF was added by once (molar ratio: TEOS:porphyrin = 1:0.05). The basic catalysis was controlled by continuous slowly adding of NH3 2.5%. The final material was a transparent red stable gel. After the wet gel was dried for 8 h at 100 8C, the color turned into green. The etalon sample was identically synthesized, without porphyrin adding and a transparent gel was obtained.
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Porphyrin entrapping by impregnation within a silica matrix derived from a two steps acid/base sol–gel process, by using TEOS as precursor. The first acid step catalysis was done identically with in situ method. The second basic step was started by slowly adding of NH3 2.5% until a transparent gel was obtained. An identical amount of solution consisting in porphyrin (TDMPP) in THF was added by once to the gel, which was firstly smashed and than vigorously stirred. After 15 min of stirring, the gelation is finished (red transparent gel). In situ sol–gel method using TEOS by sonication was conducted in acid–base catalysis by porphyrin impregnation, beneath identical previously described conditions. During the sonication (110 min), the temperature increased from 25 to 48 8C. The porphyrin–sol–gel hybrid material was gelified after 24 h, providing a red transparent gel.
3
2.5. Spectroscopic studies Absorption and fluorescence spectra were recorded at ambient temperature using 1 cm path length cells or by using the solid accessory of the luminescence spectrophotometer. All the fluorescence spectra were recorded with constant slit widths, 3 nm for excitation and 4 nm for emission. The pH values of the solutions were measured with a digital Radelkis pH-meter. The fluorescence quantum yield (FF) of porphyrin was calculated by a comparison of the area below the emission spectrum in tetrahydrofurane with that of meso-tetraphenylporphyrine (TPP), as a fluorescence standard, exciting at lex = 550 nm, by using the steady-state comparative method. A value of FF = 0.10 for TPP in tetrahydrofurane was calculated by comparison with the fluorescence spectrum in toluene using FF = 0.11 and taking into account the refractive index of the solvents according to Eq. (1):
2.3. Apparatus 1
FT-IR spectra were carried out, in the 4000–400 cm range on a JASCO 430 FT-IR apparatus, by using KBr pellets. UV–vis spectra were recorded on a UV/VIS PERKIN ELMER, LAMBDA 12 spectrometer and on a UV–vis JASCO V-650 apparatus. Fluorescence spectra were recorded in THF on a PERKIN ELMER Model LS 55 apparatus in a 1 cm cuvette. 1H NMR and 13C NMR spectra were registered on a 400 MHz and 100 MHz, respectively, BRUKER spectrometer, in CDCl3. The chemical shifts are expressed in d (ppm). The DEPT 135 experiments were done. Proton chemical shifts were internally referenced to the residual proton resonance in CDCl3 (d 7.26) and carbon chemical shifts were internally referenced to the deuterated solvent signals in CDCl3 (the 3-line triplet signal around d 77 ppm). The HPLC analysis were performed on a JASCO apparatus equipped with KROMASIL 100 SI 5um polar column, 240 mm 4 mm with MD 1510 detector, at ambient temperature, using UV detection at 420 nm. The samples were subjected to analysis (20 ml) at a flow rate of 1 ml/min with acetone/hexane of ratio 1/1 as eluent. A 212 Varian Finnigan Mat mass spectrometer was used for registering MS. Titanium tip Ultrasonic Device, working at 20 kHz frequency; output power of 1500 W was used. Pore Size Data (BJH method) were determined with QUANTACHROME Nova 1200 apparatus, by using nitrogen as adsorbate, at the temperature of liquid nitrogen 77.350 K. The method for calculation was de Boer’s (programme Quantachrome NovaWin2—Data Acquisition and Reduction for NOVA instrumentsß 1994–2003, Quantachrome Instruments, version 2.1). 2.4. Surface imaging Atomic force microscopy (AFM) investigations were carried out with a Nanosurf1 EasyScan 2 Advanced Research AFM. Atomic force microscope measurements were made with sample preparation onto a silica plate. A stiff (450 mm 50 mm 2 mm) piezoelectric ceramic cantilever (spring constant of 0.2 Nm1), with an integral tip oscillated near its resonance frequency of about 13 kHz was used in the measurements. Maximum 9 mm 9 mm scan areas were investigated, with lateral and vertical resolution of 20 nm and 2 nm, respectively. AFM data are quantitative on all three dimensions, the usual method for displaying them being by color mapping: in a gray scale, for example, dark and light tones represent the low and high features, respectively. All AFM measurements were done in ambient conditions (temperature: 21 2 8C; relative humidity: 50–70%) in contact mode or tapping mode. Some atomic force microscope (AFM) measurements were made with a non commercial Atomic Force Microscope made at Twente University of Holland. Park Scientific microcantilevers with 20 nm nominal tip radius were used in these measurements.
Fsample ¼ Fref
2 F sample Aref nsample F ref Asample n2ref
(1)
where F is the relative fluorescence quantum yield, F, A, and n are the measured fluorescence (area under the fluorescence spectra), the absorbance, and the refractive index of the solvent, respectively. 3. Results and discussion The most important analysis results that certify the structure of 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)porphyrin are given below. The significant differences comprise the yields of the final product, obtained by using various methods of synthesis. Dark violet solid; yield: 18.1% when porphyrin was obtained by Adler method [29], 36.4% when porphyrin was obtained by Lindsey method [32] and 5.5% when porphyrin was obtained by following multicomponent Adler–Longo method, previously published [44]; mp over 320 8C; FT-IR (KBr), cm1: 762 (g C–HPh), 804 (g C–HPyrrol), 1022 and 1136 (d C–HPyrrol), 1266 (n C–N), 1461 (n C5 5N), 1511 (n C5 5CPh)1586, 1679 (n C5 5CPyrrol), 2831, 2903 (CH stretching, phenyls groups), 2934, 2985 (g CH3 aliphatic) 3423 (n N–H); 1H NMR (CDCl3, 400 MHz), d, ppm: 2.70 (brs, 2H, NH), 3.96 (s, 12H, 3OCH3), 4.08 (s, 12H, 4-OCH3), 7.10–7.27 (d, 4H, m-Ph), 7.68–7.71 (d, 4H, o-Ph), 7.78 (s, 4H, o-Ph), 8.90 (s, 8H, b-Pyr); 13C NMR (CDCl3, 100 MHz), d, ppm: 148.85, 147.05, 134.73, 131.12, 130.00, 127.34, 126.75, 119.86, 118.23, 110.22, 109.41, 108.76, 56.08, 55.94; UV– vis, CHCl3 (lmax (log e): 421.27 (5.49); 518.86 (4.57); 556.38 (4.31); 592.81 (4.05); 649.91 (4.00)); TLC (Rf chloroform/dichloroethane/ethylic ether 5/5/1): 0.66; HPLC (RT, min): 3.560; MS (70 eV): m/e = 854[M]+ [C52O8N4H46]+ molecular ion). Fluorescence quantum yield FF = 0.197 0.014. The UV–vis spectrum in THF of the free base 5,10,15,20tetrakis(3,4-dimethoxyphenyl)-21H,23H-porphyrin (TDMPP) (Fig. 2) is characterized by an intense Soret band at 423.55 nm (B band) and four Q bands of smaller intensity located at 516, 552, 592 and 651 nm (Qy(1,0), Qy(0,0), Qx(1,0) and Qx(0,0), respectively). The B and Q bands are assigned to the a2u ! eg and a1u, a2u ! eg transitions, respectively. Introducing acidic condition, a tendency toward Soret band resolution into two Lorentzian bands, situated at 425 and 461 nm, respectively, can be observed (Fig. 3). The band centered on 425 nm can be unequivocally assigned to the monomer. The most important feature is that, in acidic media, the Q bands are reducing to only one, QI band, which is forbidden otherwise, red shifted towards 690 nm, and accompanied by a significant increase of the intensity. This decrease in the number of bands can be attributed to increase of the D2h symmetry of the porphyrinbase to D4h by protonation and generation of the dication species
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Fig. 2. The UV–vis spectrum of 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)21H,23H-porphyrin in THF.
Fig. 4. The allure of the absorption spectra of porphyrin during sol–gel process: porphyrin (TDMPP) in THF (line 1); first step acid catalysis pH = 3.5 (line 2); pH = 2.5 (line 3); pH = 1.5 (line 4) and second step base catalysis pH = 10 (line 5).
[45,46]. In acidic conditions the appearance of only one isosbestic point (Fig. 3) during the hydrochloric acid adding indicates the presence of a single equilibrium in solution. By increasing the acidic conditions, when the free base of the porphyrin is fully protonated, the Soret band in the UV–vis spectrum exhibits a bathochromic shift of 38 nm (l Soret dication = 461.77 nm), the QIV and QIII bands disappear while the QI grows, overlapping the QII band, (Fig. 3) [14]. All these major changes put into evidence an increase in the resonant interaction between the phenyl and pyrrole rings, followed by their slanting out of the molecule plane. The bathochromic shift in the electronic absorption spectra might be also assigned to the different molecular organization of the porphyrin molecules [47]. The UV–vis characters of hybrid porphyrin-embedded materials were almost the same as of pure porphyrin molecules (Fig. 4), showing that the molecules of porphyrin are dispersed into the new materials without significant modification regarding the aggregation of porphyrin molecules [48,5,43]. The UV–vis spectrum of the silica material without porphyrin possessed no absorption bands. With increasing acidity to pH = 3.5 and lower values of pH, two additional protons are bond to the nitrogen atoms in the center of porphyrin ring, so that the partial positive charge is induced in the central part of the molecule. A high ionic strength causes a
decrease of the monomer absorption Soret band situated around 425 nm, eventually reducing it to a pronounced shoulder. The curve 2 from Fig. 4 shows a Soret band unresolved and broadened. Hyperchromic effect manifests after porphyrin (TDMPP) encapsulation, at the gelation point, in two steps acid–base sol– gel catalysis (Fig. 4, line 5, pH = 10) in comparison with the initial porphyrin (Fig. 4, line 1), accompanied by slight broadening of the Soret band at the gelation, providing the information that a process of porphyrin aggregation occurred. It is known that Soret band of porphyrin is extremely sensitive to dimerization and that free base porphyrin in water-organic solutions are in monomer form in a concentration range of 105 M and lower. Literature reports explained [49] that during the sol– gel glasses drying, the amount of the solvent in the pores is decreasing. These are the conditions that favor the dimerization process but, on the other hand, with the progress of drying, dimerization could be gradually prevented by the steric hindrance of the forming SiO2 network and monomer porphyrin becomes preferable. By using FT-IR analysis we can answer to an important question regarding whether organic porphyrin was incorporated into the liquid sol–gel solution and subsequently trapped in the oxide matrix after gelation or if the porphyrin first reacted with the sol– gel precursors in solution and subsequently form chemical bond to the oxide after gelation.
Fig. 3. The UV–vis spectra of 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)porphyrin in THF, acidic conditions. In detail the spectrum at pH = 2.5.
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Fig. 5. FT-IR (KBr), cm1 of pure 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)porphyrin (curve a); of control silica matrix (curve b); of hybrid material obtained by acid–base sol–gel method (curve c).
Analyzing the similitude in the shape of the FT-IR spectra of hybrids that were obtained by means of the three methods: in situ, by impregnation or by sonication, we can say that organic porphyrin was incorporated into the liquid sol–gel solution and subsequently form bonds to the oxide after gelation. The FT-IR spectra of the in situ two steps acid–base catalyzed sol–gel method is presented in Fig. 5. In the spectra of control silica matrix and of hybrid porphyrin–silica material, the broad bonding mode around 1150 cm1 was attributed to the Si–O cage-like stretching mode (Fig. 5, curves b and c). In the spectrum of hybrid material registered in this region, the bands of 5,10,15,20-tetrakis(3,4dimethoxyphenyl)porphyrin (TDMPP) (Fig. 5, curve a), bendinggroups of C–H Pyrrol located at 1022 and 1136 cm1, were not clearly identifiable (in Fig. 5, curve c—their appearance is in the form of shoulders), because they overlap with the broad bands of Si–O–Si and Si–O–C exhibited by porphyrin (TDMPP)-silica hybrid material, between 970 and 1270 cm1. This feature might indicate that silica component can be bonded to the organic 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)porphyrin, at least by hydrogen bonds. Corroborating with the slight broadening of the Soret band at the gelation point in UV–vis spectra of the corresponding material (Fig. 4, curve 5) we can conclude that the dye molecules tend to aggregate also by p–p and hydrophobic interactions, as previously reported [50]. The fluorescence quantum yield (FF) of the 5,10,15,20-tetrakis(3,4-dimethoxyphenyl) porphyrin was evaluated in a solution of tetrahydrofuran and was calculated by the steady-state comparative method [51–53] using tetraphenylporphyrin (TPP) as a reference. The value determined for tetrakis(3,4-dimethoxyphenyl)porphyrin in tetrahydrofuran was FF = 0.197 0.014, a very high value. The emission spectra of this porphyrin (Fig. 6) exhibited two maxima, a strong and broad Q(0,0) fluorescence band near 654 nm, and a weaker emission band around 716 nm, assigned to Q(0,1) transition [54]. The values of lem were obtained by exciting the samples at the wavelength of 550 nm. The fluorescence spectra of the pure porphyrin were also determined in different acidic conditions and from Fig. 7, it is to be noticed that the position of the bands is not changed but the intensity is increased with the increasing of the acidity, at pH = 1.5, being almost as high as for the pure porphyrin. This is important in establishing of the conditions for first step acid catalysis because it has been found that the structure of the final gels is dependent on the structure of the gels originally formed in the solutions. As a rule [12] the gels prepared with basic catalysts are less dense than the gels with acidic catalysts or without catalysts. An explanation might be that the time of the reaction with the acidic catalyst or no catalyst in the first step is longer, and as a consequence the bulk density of the dried gels is higher.
Fig. 6. Fluorescence emission spectrum of the porphyrin (TDMPP) (line 1), in comparison with TPP (line 2), at the same concentration, 1.11 106 M, in THF. The spectra were measured with the excitation of 550 nm.
Fig. 7. Emission spectra of pure porphyrin (TDMPP) in THF (line 1); and THF–water systems pH = 1.5 (line 2); pH = 2 (line3); pH = 2.5 (line 4).
The original bands at 654 and 714–718 nm, observed in the fluorescence spectrum of the free porphyrin molecule in solution (Fig. 7) are substituted by two blue-shifted bands at 601 and 712 nm in the emission spectrum of the solid sample (Fig. 8). The important fact regarding the emission spectrum of hybrid porphyrin–silica obtained by in situ acid–base catalyzed sol–gel process is that the intensity of the main peak is almost the same in solution at the time of gelation and in the solid material, but the intensity of the second peak around 700 nm is more than three
Fig. 8. Emission spectrum of hybrid porphyrin–silica obtained by in situ acid–base catalyzed sol–gel process. Solid sample.
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Fig. 9. Emission spectra of hybrid porphyrin–silica obtained in acid–base catalyzed sol–gel process by impregnation.
times increased in comparison with that provided in solution. Final monoliths are transparent and strong glasses [14]. Regarding the emission spectra of the solid hybrid material obtained by impregnation (Fig. 9), the positions of the bands remain almost unchanged, only a slight hypsochromic shift of around 2–4 nm at each band is to be noticed, but a very important
Fig. 10. Tapping mode atomic force microscopy of pure porphyrin (TDMPP) deposited on pure silica plates (1 mm 1 mm). The samples were formed by solvent evaporation from a THF solution containing the compound.
increase of the intensity regarding both of the bands (around 80%) occurred. This situation might be predicted, because the porphyrin-base (Fig. 7, line 1) was introduced without the possibility of transforming during acid phase into dicationic derivative, which
Fig. 11. AFM images, 3D (a) in contact mode, of hybrid silica-porphyrin obtained by in situ acid/base catalyzed sol–gel method; particle analysis (b), amplitude scan (c) and topography (d) from a section of (1.32 mm 1.32 mm).
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Fig. 12. 2D (a) and 3D (b) AFM image (approximately 9 mm 9 mm), of the hybrid material obtained by impregnation of porphyrin (TDMPP) within a silica matrix derived from a two steps acid/base sol–gel process, by using TEOS as precursor (soft NanoSurf EasyScan2).
in accordance with Fig. 7 (lines 2–4) is producing the decrease of intensity in the emission spectra. In accordance with similar studies [55], AFM images of porphyrin-base (Fig. 10) on pure silica plates reveal small domain structures with an average of 33.08 nm size, which presumably corresponds to the porphyrin aggregates on the silica surface. Literature provided similar data about supramolecular assemblies based on porphyrin non-covalent interactions which have been explored in an attempt to control surface properties [56]. The AFM measurements reveal important data regarding shape, morphology and dimension of 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)porphyrin aggregates trapped in silica matrices. When the sol–gel process was conducted in situ by two steps acid–base catalysis, AFM images show that porphyrin columnar stacks of various heights were formed on silica surfaces (Fig. 11a). The dimensions of columnar microparticles are maximum 52.94 nm in length, 66.17 nm in width and 19.23 nm in height. Atomic force microscopy particle analysis of hybrid silicaporphyrin obtained by acid/base catalyzed method (Fig. 11b and c), revealed 499 grains on the material surface of 1.32 mm 1.32 mm, with the mean surface of islands of 0.00253 mm2. From topography scanning (Fig. 11d), the material seems to be ordered in oriented rows of the islands and the depths. The microporous materials obtained by the sol–gel method by impregnation with porphyrin (Fig. 12) exhibit some large pore volume, generated due to the removal of OH-related bonds during post annealing, and columnar stacks aggregations. The porphyrin stacks are in this case of maximum 143.3 nm in height and also in width. There is a distance of at least 300 nm between two stacks. In control silica matrix obtained by two steps acid base catalysis the internal mesopores have diameters less than about 3.8 nm (BET determinations) their filling being controlled by capillary condensation. As in case of a previously reported study [57], AFM of sonicated sol–gel process of synthesis of hybrid porphyrin–silica showed some pyramids with a height of about 20–30 nm and a width of about 70 nm at the base (Fig. 13). The different organization of the porphyrin array depends on the type of sol–gel method performed, so that the design of the materials might be done in order to obtain the desired topography.
Fig. 13. 3D AFM image of the surface of hybrid silica material obtained by in situ sol– gel method using TEOS with porphyrin (TDMPP), by sonication (1 mm 1 mm).
4. Conclusions Novel hybrid nanomaterials, consisting in 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)porphyrin encapsulated in silica matrices, have been prepared successfully via the two steps acid–base catalyzed hydrolysis and condensation of tetraethylorthosilicate using different approaches of the sol–gel process: in situ, by impregnation and by sonication. Final monoliths are transparent and strong glasses and the photochemical properties of porphyrins entrapped in silica inorganic matrices are described. Hyperchromic effect manifests after porphyrin encapsulation, at the gelation point, in two steps acid–base sol–gel catalysis in comparison with the initial porphyrin, also accompanied by slight broadening of the Soret band, providing the information that a process of porphyrin aggregation occurred. The important fact regarding the emission spectrum of hybrid porphyrin–silica obtained by in situ acid–base catalyzed sol–gel process is that the intensity of the main peak is almost the same in solution at the time of gelation as in the solid material, but the intensity of the second peak around 700 nm is more than three times increased in comparison with that provided in solution and
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the main band is blue-shifted with 50 nm in the emission spectrum of the solid sample. Regarding the emission spectra of the hybrid material obtained by impregnation, the positions of the bands remain almost unchanged, but a very important increase of the intensity regarding both of the bands (around 80%) occurred. The topography of the hybrid nanomaterials depends on the type of sol–gel method performed. When the sol–gel process was conducted in situ, AFM images show that porphyrin columnar stacks were formed on silica surfaces. The microporous materials obtained by the sol–gel method by impregnation exhibit some large pore volume and irregular stacks aggregations, but in case of sonicated sol–gel process AFM showed some pyramidal nanostructures. Acknowledgement Authors are grateful to CNMP Romanian National—PN II Programme because this work has been supported by Project No. D11-055/2007. References [1] L.C. Klein, Processing of nanostructured sol–gel materials, in: A.S. Edelstein, R.C. Cammarata (Eds.), Nanomaterials: Synthesis, Properties, and Applications, Institute of Physics Publishing, Bristol and Philadelphia, 1996, pp. 147–164. [2] R.D. Shoup, Sol–Gel Processes in: Engineered Materials Handbook, vol.4. Ceramics and Glasses, ASM Int., USA, 1991, pp. 445–452. [3] A.C. Pierre, Ceram. Bull. 70 (1991) 1281–1288. [4] C.J. Brinker, G.W. Scherrer, Sol–Gel Science: The Physics and Chemistry of Sol–Gel, Academic Press, New York, 1990, pp. 839–841. [5] E. Fagadar-Cosma, C. Enache, G. Fagadar-Cosma, C. Savii, J. Optoelectron. Adv. Mater. 9 (2007) 1878–1882. [6] G.M. Chow, L.K. Kurihara, in: C.C. Koch (Ed.), Processing Chemical Synthesis and Processing of Nanostructured Powders and Films. Part. 1: In Nanostructured Materials: Processing Properties, and Potential Applications, Noyes Publications/William Andrew Pub., Norwich: NewYork, 2002, pp. 19–22. [7] C. Zhao, P. Zhang, S. Lu, J. He, X. Wang, J. Mater. Sci. 42 (2007) 9083–9091. [8] P.J. Lopez, C. Gautier, J. Livage, T. Coradin, Curr. Nanosci. 1 (2005) 73–83. [9] T. Islam, H. Saha, Sens. Transducers J. 72 (2006) 731–739. [10] J. Tachibana, M. Chiba, M. Ichikawa, T. Imamura, Y. Sasaki, Supramol. Sci. 5 (1998) 281–287. [11] J. Tanihara, K. Ogawa, Y. Kobuke, J. Photochem. Photobiol., A 178 (2006) 140–149. [12] K. Kamitani, M. Uo, H. Inoue, A. Makishima, J. Sol–Gel Sci. Technol. 1 (1993) 85–92. [13] P. Behrens, A.M. Glaue, Monatsh. Chem. 133 (2002) 1405–1412. [14] M.A. Garcıa Sanchez, S.R. Tello, S.R. Sosa, F.A. Campero, J. Sol–Gel Sci. Technol. 37 (2006) 93–97. [15] J. Dargiewicz-Nowicka, M. Makarska, M.A. Villegas, J. Legendziewicz, St. Radzki, J. Alloys Compd. 380 (2004) 380–388. [16] Y. Inaba, K. Ogawa, Y. Kobuke, J. Porphyrins Phthalocyanines 11 (2007) 406–417. [17] S. Banfi, E. Caruso, E. Fieni, L. Buccafurni, M.B. Gariboldi, R. Ravizza, E. Monti, J. Porphyrins Phthalocyanines 10 (2006) 1319–11319. [18] I. Roy, T.Y. Ohulchanskyy, H.E. Pudavar, E.J. Bergey, A.R. Oseroff, J. Morgan, T.J. Dougherty, P.N. Prasad, J. Am. Chem. Soc. 125 (2003) 7860–7865. [19] T. Konishi, M. Horie, T. Wada, S. Ogasawara, J. Kikuchi, A. Ikeda, J. Porphyrins Phthalocyanines 11 (2007) 342–347.
[20] H. Imahori, Y. Kashiwagi, T. Hasobe, M. Kimura, T. Hanada, Y. Nishimura, I. Yamazaki, Y. Araki, O. Ito, S. Fukuzumi, Thin Solid Films 451–452 (2004) 580–588. [21] T. Hasobe, S. Hattori, P.V. Kamat, Y. Urano, N. Umezawa, T. Nagano, S. Fukuzumi, Chem. Phys. 319 (2005) 243–252. [22] A. Graja, I. Olejniczak, A. Bogucki, D. Bonifazi, F. Diederich, Chem. Phys. 300 (2004) 227–232. [23] Y. Zeng, C. Li, C. Tang, X.B. Zhang, G. Shen, R. Yu, Electroanalysis 18 (2006) 440– 448. [24] Y. Wang, H. Xu, J. Zhang, G. Li, Sensors 8 (2008) 2043–2081. [25] S.K. Lee, I. Okura, Anal. Chim. Acta 342 (1997) 181–188. [26] A.T. Papacı´dero, L.A. Rocha, B.L. Caetano, E. Molina, H.C. Sacco, E.J. Nassar, Y. Martinelli, C. Mello, S. Nakagaki, K.J. Ciuffi, Colloids Surf., A 275 (2006) 27–35. [27] F.L. Benedito, S. Nakagaki, A.A. Saczk, P.G. Peralta-Zamora, C.M.M. Costa, Appl. Catal., A 250 (2003) 1–11. [28] P.A. Rothmund, J. Am. Chem. Soc. 58 (1936) 625–627. [29] A.D. Adler, F.R. Longo, J.D. Finarelli, J. Goldmacher, J. Assour, L. Korsakoff, J. Org. Chem. 32 (1967) 476–1476. [30] N. Dattagupta, D. Malakar, C. Jenkins, C. Strange, Bull. Chem. Soc. Jpn. 61 (1988) 2274–2276. [31] S. Neya, N. Funasaki, J. Heterocycl. Chem. 34 (1997) 689–690. [32] J.S. Lindsey, I.C. Schreiman, H.C. Hsu, P.C. Kearney, A.M. Marguerettaz, J. Org. Chem. 52 (1987) 827–836. [33] J.S. Lindsey, R.W. Wagner, J. Org. Chem. 54 (1989) 828–836. [34] F. Li, K. Yang, J.S. Tyhonas, K.A. Maccrum, J.S. Lindsey, Tetrahedron 53 (1997) 12339–12360. [35] S. Shanmugathasan, C. Edwards, R.W. Boyle, Tetrahedron 56 (2000) 1025–1046. [36] V. Kra´l, J. Kra´lova´, R. Kapla´nek, T. Brˇı´za, P. Marta´sek, Physiol. Res. 55 (Suppl. 2) (2006) S3–S26. [37] J.L. Sessler, M.R. Johnson, Angew. Chem. Int. Ed. Engl. 26 (1987) 678–680. [38] J.L. Sessler, S. Piering, Tetrahedron Lett. 28 (1987) 6569–6572. [39] A. Boudif, M.A. Momenteau, J. Chem. Soc. Perkin Trans. 1 (1996) 1235–1242. [40] Y. Lin, T.D. Lash, Tetrahedron Lett. 36 (1995) 9441–9444. [41] T.D. Lash, T.J. Roper, Tetrahedron Lett. 35 (1994) 7715–7718. [42] E. Fagadar-Cosma, C. Enache, D. Dascalu, G. Fagadar-Cosma, R. Gavrila, Optoelect. Adv. Mater. Rapid Commun. 7 (2008) 437–441. [43] E. Fagadar-Cosma, C. Enache, I. Armeanu, D. Dascalu, G. Fagadar-Cosma, M. Vasile, I. Grozescu, Mater. Res. Bull. 44 (2009) 426–431. [44] E. Fagadar-Cosma, L. Cseh, V. Badea, G. Fagadar-Cosma, D. Vlascici, Comb. Chem. High Throughput Screening 10 (2007) 466–472. [45] Z. Ou, H. Sun, W. Zhu, Z. Da, K.M. Kadis, J. Porphyrins Phthalocyanines 12 (2008) 01–10. [46] E. Fagadar-Cosma, C. Enache, R. Tudose, I. Armeanu, E. Mosoarca, D. Vlascici, O. Costisor, Rev. Chim. (Bucharest, Rom.) 58 (2007) 451–455. [47] M. Tonezzer, A. Quaranta, G. Maggioni, S. Carturan, G. Della Mea, Sens. Actuators B 122 (2007) 620–626. [48] P.J. Meadows, E. Dujardin, S.R. Hall, S. Mann, Chem. Commun. (2005) 3688– 3690. [49] J. Dargiewicz, M. Makarska, S. Radzki, Colloids Surf. A 208 (2002) 159–165. [50] T. Milic, J.C. Garno, J.D. Batteas, G. Smeureanu, C.M. Drain, Langmuir 20 (2004) 3974–3983. [51] J.N. Demas, G.A. Crosby, J. Phys. Chem. 75 (1971) 991–1024. [52] D. Tatman, P.A. Liddel, T.A. Moore, D. Gust, A.L. Moore, Photochem. Photobiol. 68 (1998) 459–466. [53] A.T.R. Williams, S.A. Winfield, J.N. Miller, Analyst 108 (1983) 1067–1071. [54] A.P.J. Maestrin, A.C. Tedesco, C.R. Neri, M.E.F. Gandini, O.A. Serra, Y. Iamamoto, J. Braz. Chem. Soc. 15 (2004) 708–713. [55] H. Imahori, A. Fujimoto, S. Kang, H. Hotta, K. Yoshida, T. Umeyama, Y. Matanoa, S. Isodad, Tetrahedron 62 (2006) 1955–1966. [56] S. Yoshimoto, K. Itaya, J. Porphyrins Phthalocyanines 11 (2007) 313–333. [57] A. Klyszcz, M. Lauer, M. Kopaczynska, C. Bottcher, F. Gonzaga, J.H. Fuhrhop, Chem. Commun. (2004) 2358–2359.
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