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Porphyrazines http://macroheterocycles.isuct.nj Paper
DOI: 10.6060/mhc2012.120678d
Synthesis and Study of Physicochemical Properties of New Substituted Tetrathieno[2,3-b]porphyrazines
Tatiana V. Dubmma,ab@ Daria V. Dyumaeva,a Stanislav A. Trashin,b Marina V. Sedova,c Alexey B. Karpo,d Vitaly I. Krasovskii,d and Larisa G. Tomilovaab
aDepartment of Chemistry, M.V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation bInstitute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation
cInstitute for Theoretical and Applied Electromagnetics, Russian Academy of Sciences, 125412 Moscow, Russian Federation dA.M. Prokhorov Institute of General Physics, Russian Academy of Sciences, 119991 Moscow, Russian Federation @Corresponding author E-mail: [email protected]
Synthetic approach to a new substituted tetrathieno[2,3-b]porphyrazine, its planar and sandwich-type complexes was developed. Aggregation phenomena and spectral properties of the target compounds were investigated by UV-Vis spectroscopy and AFM. Electrochemical behaviour of the Zn complex was studied in a wide range of potentials (-2.0^2.0 V). The NLO properties of Zn complex was studied by the z-scan approach.
Keywords: Porphyrazines, nonlinear optical properties, electrochemistry, sandwich-type complexes, UV-Vis spectroscopy.
Introduction
Tetrathieno[2,3-b]porphyrazines are the less studied analogues of phthalocyanines.[1] The presence of a sulphur-containing heterocyclic moiety in the macrocycle improves photoconductivity[2] and nonlinear optical (NLO) properties.[3] Therefore such compounds are of importance for a range of functional applications including photovoltaic cells,[2b] photodynamic therapy (PDT),[4] and optical data storage devices.[5] Previously reported unsubstituted tetrathieno[2,3-b]porphyrazines exhibit low solubility in organic solvents, and the synthetic strategy is inefficient (yield < 16%).[6] Synthesis of alkoxy-substituted porphyrazines is also of low yield (15-20 %) and includes a complicated synthesis of initial dinitrile.[2a] The present paper focuses on the synthesis of highly-soluble substituted tetrathieno[2,3-b]porphyrazines and investigation of spectral and electrochemical properties.
Experimental
Column chromatography was carried out on neutral MN-Aluminiumoxid. Preparative TLC was performed using Merck Aluminium Oxide F254 neutral flexible plates. The electrolyte [Bu4N]+[BF4]" (Sigma-Aldrich) was recrystallized twice from ethyl acetate/hexane (9:1, V/V) and dried under vacuum at 70 °C. o-Dichlorobenzene (DCB, 99%, Sigma-Aldrich, HPLC-grade) for voltammetric and specrtoelectrochemical studies was used as received. All other reagents and solvents were obtained or distilled according to standard procedures. The salts Mg(OAc)2-4H2O; Zn(OAc)2-4H2O; Lu(OAc)3-4H2O was dried immediately before use in a vacuum desiccator for 4 h at 90 °C. All reactions were TLC and UV/Vis controlled until complete disappearance of the starting reagents if not additionally specified.
Electronic absorption (UV-Vis) spectra were recorded on a ThermoSpectronic Helios-a spectrophotometer using quartz cells (0.5 x1cm). MALDI-TOF mass spectra were taken on a VISION-2000 mass spectrometer with 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]-malonitrile (DCTB) as the matrix. High resolution MALDI mass spectra were registered on a Bruker ULTRAFLEX II TOF/TOF instrument with DCTB as the matrix. 1H and 13C NMR spectra were recorded on a Bruker "Avance 400" spectrometer (400.13 and 100.61 MHz respectively) at 20oC (if not additionally specified). Chemical shifts are given in ppm relative to SiMe4.
Electrochemical measurements were carried out using IPC-Pro (Econix, Moscow, Russia) and EmStat (Palm Instrument BV, Utrecht, the Netherlands) potentiostats. Cyclic voltammetry (CVA) and square-wave voltammetry (SWVA) were performed in a conventional three electrode cell using Pt-disk (2.0 mm in diameter) working and Pt-foil counter electrodes.A calomel reference electrode (SCE, 3M NaCl) was connected to the solution through a salt-bridge and a Luggin capillary, whose tip was placed close to the working electrode. The junction potentials were corrected by ferrocenium+/ ferrocene (Fc+/Fc) couple each time after a series of measurements (£1/2(FeFc2) = 0.592 V). Freshly distilled dichloromethane (purium, Reachim Russia) and o-dichlorobenzene (DCB, 99% Sigma-Aldrich, HPLC-grade) freshly passed through an Al2O3 layer were used as solvents, and 0.15 M solution of Bu4NBF4 (Sigma-Aldrich, dried under vacuum at +80oC) in o-dichlorobenzene containing (2^10)-10-4 M of sample was bubbled with argon for 20 min before measurements. Blank voltammograms were recorded in the same background solution.
AFM studies were carried out by means of a Solver-P47H (NT-MDT) microscope. Tapping mode and a high accuracy composite silicon/polysilicon HA_NC probe for non-contact AFM were applied to obtain images. Menzel-Gläser cover slips (18x18 mm) were employed as the substrate. The rounding-off radius of the probe was less than 10 nm.
2-Iodo-4,5,6,7-tetrahydrobenzo[^]thiophene-3-carbonitrile was synthesized according to the published procedures.[6,7]
4,5,6,7-Tetrahydrobenzo[b]thiophene-2,3-dicarbonitrile (1).
(Xj CN
icfc*
a2 1
A mixture of 2-iodo-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carbonitrile (2.400 g, 8.3 mmol) and CuCN (1.850 g, 0.020 mol) were refluxed in DMF (40 ml) for 10 h (TLC-control: Al2O3, C6H6: n-hexane (1:1 V/V)). The reaction mixture was cooled to room temperature and water was added. The product was collected by extraction with dichloromethane. The organic layer was dried with CaCl2. The solvent was evaporated and the resulting solid was purified twice by column chromatography (Al2O3, CHCl3). This yielded 1 as a pale yellow solid (1.020 g, 64%). mp 82.6°C (lit.,[6] 82-83°C), ^=0.4 (Al2O3, C6H6: n- hexane (1:1 V/V)), 1H NMR (400 MHz, CDCl3) 5H ppm: 1.85 - 1.93 (m, 4H, ß12-CH2), 2.73 (t, J = 5.7 Hz, 2H, a1-CH2), 2.81 (t, J = 5.7 Hz, 2H, afCH^. 13C NMR (100 MHz, CDCl3) 5c ppm: 21.38, 22.39 (ß12-CH2), 24.36, 25.22 (a12-CH2), 111.60 and 111.93 (CN), 113.70 (C2), 119.47 (C3), 138.39 (C4), 145.71 (C5).
2,3,8,9,14,15,20,21 -Octakis[4 ',5',6',7 '-tetrahydrobenzo]-tetra-2,3-thiophenophorphyrazine magnesium (2).
a2CH2
Ri> R2 ~ "[CH2U"
A mixture of 1 (0.200 g, 1.064 mmol), Mg(OAc)2-4H2O (0.143 g, 0.668 mmol) and lithium methoxide (0.019 g, 0.500 mmol) were refluxed in n-octanol (3.5 ml) for 8 h (TLC-control: Al2O3, C6H6). The reaction mixture was cooled to room temperature and a mixture MeOH:H2O (10:1 V/V) was added. A dark green precipitate was filtered and washed with water and MeOH. This yielded 2 (0.093 g, 45%). UV-Vis (THF) Xmax nm (lge): 663 (4.49), 639 (3.98), 603 (3.77), 369 (4.35). 1H NmR"(400 MHz, CDCl3:MeOH 100:1 V/V) Sh ppm: 1.77 (m, 16H, P12-CH2), 2.65-2.70 (m, 16H, a12-CH2). MS-MALDI-TOF m/z: 776 ([M]% 100%).
2,3,8,9,14,15,20,21 -Octakis[4 ',5',6',7 '-tetrahydrobenzo]-tetra-2,3-thiophenophorphyrazine zinc (3).
A mixture of 1 (0.070 g, 0.370 mmol), Zn(OAc)2 4H2O (0.047 g, 0.185 mmol) and lithium methoxide (0.007 g, 0.185 mmol) were refluxed in n-octanol (1.5 ml) for 5 h (TLC-control:
Al2O3, C6H6). The reaction mixture was cooled to room temperature and a mixture MeOH:H2O (10:1 V/V) was added. A dark green precipitate was filtered and washed with water and MeOH. This yielded 3 (0.061 g, 80%). UV-Vis (THF) Xmax nm (lge): 665 (4.6), 603 (3.9), 367 (4.4). 1H NMR (400 MHz, Py-d^ Sh ppm: 2.02 (m, 8H, P2-CH2), 2.08 (m, 8H, P1-CH2), 3.11-3.1(5 (in, 8H, a2-CH2), 3.84-3.98 (m, 8H, a1-CH2). HRMS-MALDI-TOF/TOF m/z: [M]+ ■ calculated for C40H34N8S4Zn: 818.4057; found: 818.4082.
2,3,8,9,14,15,20,21-0ctakis[4',5',6',7 '-tetrahydrobenzo]-25H,27H-tetra-2,3-thiophenophorphyrazine (4).
a) Approach with concentrated sulfuric acid. The magnesium complex 2 (0.011 g, 0.014 mmol) was dissolved in concentrated sulfuric acid (3 ml). This solution was poured into the ice. At the same time the green precipitate was formed. This precipitate was filtered and washed with water and MeOH to give 4 (0.004 g, 38%). UV-Vis (THF) Xmax nm (lge): 699 (4.60), 655 (4.54), 352 (4.55). HRMS-MALDI-TOF/TOF: m/z [M]+ ■ calculated for C40H34N8S4: 754.2912 [M]+ ■; found: 754.3190.
b) Approach with concentrated trifluoroacetic acid. The magnesium complex 2 (0.011 g, 0.014 mmol) was dissolved in concentrated trifluoroacetic acid (3 ml). This solution was poured into the ice. At the same time the green precipitate was formed. This precipitate was filtered and washed with water and MeOH to give 4 (0.005 g, 48%). The characteristics were identical with those obtained by method (a).
c) Approach with pyridine hydrochloride. A mixture of 3 (0.030 g, 0.0370 mmol) and pyridine hydrochloride (0.012 g, 0.10 mmol) were refluxed in pyridine (600 ^l) for 3 h. The reaction mixture was cooled to room temperature and a mixture MeOH:H2O (10:1 V/V) was added. A dark green precipitate was filtered and washed with water and MeOH. This yielded 4 (0.026 g, 93%). The characteristics were identical with those obtained by method (a).
2,3,8,9,14,15,20,21-0ctakis[4',5',6',7 '-tetrahydrobenzo]-tetra-2,3-thiophenophorphyrazinatolutetium acetate (5).
Ri> R2 ~ -[CH2]4-
A mixture of 4 (12 mg, 0.016 mmol), Lu(OAc)3 4H2O (3 mg, 0.007 mmol) and lithium methoxide (0.004 g, 0.105 mmol) were heated in the mixture TCB:C16H33OH (1:1 V/V; Vtotal = 300^l) at the temperature range: 190-230°C for 2.5 h (TLC-control: Al2O3, C6H6). The reaction mixture was cooled to room temperature and a mixture MeOH:H2O (5:1 V/V) was added. A dark green precipitate was filtered and washed with water and MeOH. The compound 5 was separated using preparative TLC (Al2O3, C6H6). This yielded 5 (0.010 g, 63%). Rf=0.3 (Al2O3, C6H6). UV-Vis (THF) Xmax nm (lge):
664 (4.53), 604 (3.98), 362 (4.43). HRMS-MALDI-TOF/TOF: m/z [M-OAc-H]+ ■ calculated for C40H31LuN8S4: 926.0962; found: 926.0688.
exo
,-naHendo°Ut
pHem pHendo
out
i
out
Ri V R? Rl
RK R2
Cu
aCHj
VN 'N-/ aCH2in N0 ■/ ,N
Ki Ri 1
Ri
/ R2 RI
Lu
s—r-Ri
Hjp&x-*
Rl> r2 ~ -[CH2]4-
Tris[2,3,8,9,14,15,20,21-octakis[4',5',6',7'-tetrahydro-benzo]tetra-2,3-thiophenophorphyrazine] dilutetium (6) was separated using preparative TLC (Al2O3, C6H6). This yielded 6 (0.005 g, 36%). Rf=0.8 (Al2O3, C6H6). UV-Vis (THF) ^ nm (lgs): 698 (3.85), 656 (4.59), 551 (3.67), 371 (4.45), 310 (4.37). 1H NMR (400 MHz, CDCl3) 5H ppm: 1.96 (m, 16H, P-Hexoout), 2.09 (m, 16H, P-H^-), 2.32 (m, 16H, p-Hin), 2.60 (m, 16Hra-Hxoout), 2.84 (m, 16H, (i-Heiidoout), 3.55 (m, 16H, a-Hin). HRMS (MALDI-TOF/TOF) m/z: [M]+™ "calculated for C120H96Lu2N24S12: 2608.9210; found: 2608.8909.
Results and Discussion
4,5,6,7-Tetrahydrobenzo[b]thiophene-2,3-dicarbo-nitrile was chosen as the starting compound. This dinitrile was obtained by a standard synthetic route.[6,7] Replacement of 1,1,3,3-tetramethylurea[6] by DMF at the stage of cyanation allowed for an increase in yield from 47 to 64%. According to the literature data,[6] tetrathieno[2,3-b]porphyrazines can exist as a mixture of four possible isomers (excluding the isomers of cyclohexene moieties), C4h, CS, D2h and C2V, which cannot be separated. Four similar randomers also occur for 1,2-naphthalocyanines.[8,9]
The porphyrazine complexes were synthesised from the dinitrile 1 and acetates of corresponding metals in boiling n-octanol upon addition of lithium methoxide base (Scheme 1). Magnesium and zinc ions were chosen for the subsequent formation of ligands.[10] Formation of porphyrazines was not observed under mild conditions in a boiling isoamilic alcohol. Metal-free porphyrazine was obtained by the method discribed for phthalo- and naphthalocyanine ligands,[10c,11] which involved treatment of magnesium complex 2 with strong concentrated acids (Scheme 1). However, partial destruction of thiophene moieties under polymerisation in concentrated acid led to a low yield of target compound.
Treatment of magnesium complex 2 with a weaker acetic acid did not yield 4. Demetallation was done under mild conditions, as recently reported for zinc phthalocyanines. This approach includes a reaction between zinc complex and pyridine hydrochloride in boiling pyridine and is based on formation of a ternary pyridine- Zn - Pc complex with square pyrimidal zinc coordination.[10a] Present work is the first successful example of the synthesis of porphyrazine compounds by such route.
Phthalocyanine and porphyrazine complexes of rare earth elements (REE) find a large range of applications in optics and electronics.[12] In light of that, we have chosen to synthesize a lutetium complex of 4 as our first example. Tetrathieno[2,3-b]porphyrazine lutetium 5 was obtained by a reaction of ligand 4, lutetium acetate and lithium methoxide in the mixture of cetyl alcohol and TCB (1:1 volume ratio) (Scheme 1).
Substituted triple-decker lutetium porphyrazine 6 was separated as a by-product in the synthesis of 5. Noteworthy, this is the first example of sandwich-type porphyrazine with annelated heterocyclic ring. Formation of the double-decker complex 7 was confirmed by MALDI TOF mass spectrometry, but all attempts to isolate the product were unsuccessful. Perhaps, this is due to the low stability of ^-radical thienoporphyrazine structures. Even the standard synthetic route (Lu acetylacetonate; lithium methoxide; 190°C; n-octanol)[13] did not yield double-decker complex. Novel porphyrazines 2-6 were characterized by high resolution MALDI-TOF mass spectrometry, UV-Vis and 'H NMR spectroscopy.
UV-Vis spectra of the obtained porphyrazines are very instructive. Metal-free 4 exhibits 0-band splitting (Figure 1a), that can be attributed to the non-degenerated LUMO orbital.[14] In contrast, 0-bands in complexes 2, 3, 5 were not split (Figure 1 and Table 1). This result is in accord with the literature data[15] and DFT calculations[14] for porphyrazines. The absence of 0-band splitting and the values of full width at half maximum (FWHM) for porphyrazine complexes in THF (Table 1.) allow to conclude that C4h and C2V randomers[9] predominate in the mixture. A weak intensity broad band, which is characteristic for phthalocyanines and porphyrazines that containing chalcogenide atoms, was observed in the range of 400-450 nm. This band refers to the charge transferfrom thiophene cycles to porphyrazine core.[3a] Compared to unsubstituted thieno[2,3-b]porphyrazine,[6] 0-bands for tetrahydrobenzo substituted complexes are bathochromically shifted. This phenomenon can be explained by the donor effect of substituents. Nature of the central metal in porphyrazine complexes did not influence the 0-band position (Figure 1), as was also the case for monophthalo- and naphthalocyanines.[11] 0-band of the metal-free compound 4 had a bathochromic shift with respect to 0-bands of complexes 2, 3 and 5. The triple-decker complex 6 exhibits 0-band splitting and a hypsochromic shift of the main absorption maximum as compared to those of monoporphyrazines. Similar features have been previously reported for triple-decker phthalocyanine complexes[16,17] and are due to the interaction of the inner and external
deck.[13]
The spectra of porphyrazines 2-5 in a non-coordinating solvent (C6H6) exhibit aggregation behaviour that is
TVCN Ri S
Mg(0Ac)2*4H20/Me0Li//' 1 j m-octanol,reflux
Zn(OAc) 2*4H20 / MeOLi / . n -octanol,reflux
Riv_<R2 c^Ri
i) 38% yield
ii) 48% yield
45% yield 80% yield R, R>
TSL, „N-/ ^tVn^CS
Rl s 3 Ri Rl
pyridine*HCl/ pyridine, reflux
StrI
i)H2S04
ii)CF3œoH
RlJ2
SV-^N-
Vn hn-/
Rf S
■R2
R2 ri
OAc
R-iv-^ I s^-Ri
R1.R2 ~ -[CH2]4-
190 - 230 °C Lu(OAC)3*4H20
1 MeOLi/TCB/C16H33OH
+
Ri R2
isáU^éX
3=N N^T
Ri
R2
+
R2
Rf^ iï ¿2 Rl
ÉÚ
R^Rl Ri^2 /v s Rl
/ \Ji Rl 6 R2 Rl 36% yield
=N
r2
Rf^S'
Ri
R2
V R2 R1 Lu
Ri
R2~ Ri*
;N
¡I \ s-rRl
r2 Rl
(trace yield)
Scheme 1. Synthesis of thienoporphyrazine complexes 2-7 (the structures of complexes are shown for one isomer).
manifested in broadening of 0-bands and decreasing of the 0-band:5-band intensity ratio ///max (Table 1). Due to the steric effect of external decks the aggregation was minimal in the case of the triple-decker compound 6.
The aggregation effect was stronger in solid films of 6. Films possessed an "island-type", large-grain structure (Figure 2). Grain size depended on the coordination effect of the solvent. In the case of C6H6 the grain size was 45 nm in height and 200 nm in width. For highly-coordinating THF, grain size was 7 nm in height and from 60 to 80 nm in width.
Electrochemical behaviour of complex 3 in o-DCB was investigated (Figure 3). The square-wave voltammogram (SWVA) exhibited three reduction potentials at -0.915, -1.295 and -1.735 V and two oxidation potentials at +0.835 and +1.520 V. In cyclic voltammogram (CVA), only highly-reversible redox processes Redp Red2 and Oxj were
observed, which is likely due to the lower sensitivity of the method. Under the potential scanning until 1.6 V and higher, poor reversibility of the Ox2 process resulted in a decrease of intensity and a shift of the reverse peak of Ox1.
Investigation of nonlinear optical properties was carried out using a well known Z-scan technique.1181 The scheme of the experiment is presented in Figure 4.
In our study we used a Nd:YAG laser operated at the TEM00 mode with the pulse duration of t = 350 ps (halfwidth at e'1 intensity) at the repetition rate of 5 Hz. To obtain the second harmonic at 532 nm we used an ADP-crystal. The beam was tightly focused and the beam radius (halfwidth at e"2 intensity) was ra0=30| at the focus. The energy of the pulse was E0 = 38|jJ. Measurements with closed aperture help to reveal the characteristics of the nonlinear refraction. The measurements with open aperture reveal the characteristics of the non-linear absorption.
Figure 1. UV-Vis spectra of thienoporphyrazines 3, 4 and 6 in THF.
Figure 2. AFM phase contrast images of thin films of compound 6 deposited from a THF solution (a) and from a C6H6 solution (b) (C = 10-6 M).
Table 1. UV-Vis spectral data for compounds 2-6.
Full Width at Half Full Width at Half Maximum
Compound X (I/I ), nm in THF v max^5 X (I/I ), nm in C6H6 ^ max^' 6 6 Maximum (FWHM) for Q-band (nm) in THF (FWHM) for Q-band (nm) in C6H6
2 663 (1.00); 639 (0.31); 603 (0.19); 369 (0.77) 668 (0.83); 611 (0.24); 373 (1.00); 306 (0.59) 20 (663) 27 (668)
3 665 (1.00); 603 (0.23); 672 (1.00); 641 (0.42); 619 21 (665) 26 (672)
367 (0.55) (0.41); 363(0.94); 310 (0.57)
4 699 (1.00); 655 (0.86); 700 (0.92); 656 (0.87); 638
352 (0.88) (0.80); 358 (1.00); 312 (0.78) 15 (699) 16 (700)
5 664 (1.00); 604 (0.28); 362 (0.79) 667 (0.97); 605 (0.34); 363 (1.00); 305 (0.88) 20 (664) 26 (667)
6 698 (0.18); 656 (1.00); 697 (0.19); 655 (1.00); 550
551 (0.12); 371 (0.72); (0.15); 371 (0.81); 314 19 (698) 20 (655)
310 (0.60) (0.60)
Figure 3. Square wave (a) and cyclic (b) voltammograms of 3 in o-DCB.
Figure 4. The Z-scan setup. F- filters, BS - beam splitter, Dp D2 and D3 are photodetectors, A - aperture, S - sample.
Table 2. NLO measurements data for compound 3.
Compound Rex(3) (esu) Imx(3)(esu) X (nm) I (GW/cm2)
26 3.45-10-14 11.5-10"14 532 2.5
Here we present the best result, which was reached for Zn complex. In Table 2 there are the real part of nonlinear
optical susceptibility, corresponded to nonlinear refraction, and the imaginary part of nonlinear optical susceptibility, corresponded to nonlinear absorption. This compound posseses the negative nonlinearity (Figure 5), which increases under the increase in the concentration of target compound in solution. Noteworthy, that metal-free and triple-decker compounds did not show remarkable non-linearity for the similar concentrations.
As one can see from the open-aperture z-scan (Figure 5a) the sample shows reverse saturable absorption. To interpret the experimental data it is convenient to use the five-level model. The five-level model is represented with the Jablonski diagram which describes processes of excitation and relaxation in the molecule. In this model commonly only one-photon processes are considered. The scheme of the model is presented in Figure 6. The ground state is signed as S0.
Figure 6. Jablonski diagram of excitation and relaxation processes in a molecule.[19]
Absorption of the photon at 532 nm leads to the transition of the electron to the vibronic sublevel of the first excited singlet state S1. The lifetime of the vibronic sublevel is of subpicosecond range, so only the direct transition S0 ^ S1 can be considered. The electrons from S1 can relax either to the ground state, with the lifetime t0, or to the triplet state T1 via intersystem crossing, with the
Figure 5. An open (a) and closed (b) aperture Z-scans measured for Zn complex in C6H6 (C = 6-10-5 M).
lifetime tisc. Under the influence of the incident radiation excited electrons at states Sx and T will transit to upper excited states Sn and Tn, respectively. The population dynamics of all mentioned states is described by system of rate equations:
dN,
I N
dt
0 =-a0N^ + -
N
ha
dNsl ^ N I ^ N I NS1 NS1 + NS2
-= ct0Ng--CT1NS1------1--
dt ha ha t0 tISC tS2
dNS2 =„ N _L-N2
,, _ CT1NS1 ,
dt ha tS2
= a2NT1^ dt ha xT,,
the nonlinear optical properties and they are the subject of further investigation.
Conclusions
In conclusion, novel highly-soluble substituted porphyrazines were synthesised in high yields (45-80%). The synthetic route to the thieno[2,3-è]porphyrazine complexes as a perspective building-blocks for sandwich-type porphyrazines was developed. Heterocyclic ring annelated sandwich-type porphyrazine complex was synthesised for the first time. Spectral properties and aggregation phenomena of target compounds were investigated by UV-Vis and AFM techniques. Electrochemical behaviour of the Zn complex was studied by CVA and SWWA and the presence of reversible redox processes was shown. The presence of induced absorption shows, that Zn complex can be used as an optical limiter.
Acknowledgements. The research was supported by the Russian Foundation for Basic Research (Grant No. 08-0300753), and the programme of the Presidium of the Russian Academy of Science "Development of a strategy of organic synthesis and creation of compounds with valuable and applied proprieties".
where N. is the population of the i-th state, c0 is the ground state absorption cross-section, is the first excited singlet state absorption cross-section, is the first excited triplet state absorption cross-section, t . is the lifetime of the i-th state and t/sc is the intersystem crossing lifetime. The absorption in the sample is governed by the Beer's law:
T7 = -CT0ING -CT1INS1 -^2INT1
dz'
where z' is the coordinate inside the sample. Where the first term describes the absorption of the ground state and the other two describe the absorption of excited singlet and triplet state, respectively. The transmittance of the pulse is determined by the formula
œ œ
J dt J I0ut(r,z,t)rdr T(z) = --œ 0
œ œ
J dt J Iin(r,z,t)rdr
where I. and I , are the intensities of incident and transmitted
in out
pulses, respectively. Calculating transmittance for each z-position yields the z-scan curve.
The results we present in the Table 2 are calculated with the %(3) - formalism which doesn't describe full nature of the processes which take place during the illumination with intense laser pulse. It is necessary to use the five-level model. However, using of the model implies that lifetimes of the excited states are known. To calculate the values of and time-resolved measurements are needed. These measurements are very important to characterize
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Received 08.06.2012 Accepted 18.06.2012
