不对称五氮齿大环铟和铅配合物的合成及其光物理特性

郭丰启 王夺元**
（中国科学院北京感光化学研究所 100101）

Abstract The synthesis and characterization of asymmetric pentaazadentate macrocyclic indium and lead complexes are reported. The electronic absorption spectra, the fluorescence spectra, the fluorescence quantum yields and the lifetimes of the first singlet excited states are measured.
Key word asymmetric pentaazadentate metal complexes, electronic absorption spectrum, fluorescence quantum yield, fluorescence lifetime
摘要 本文报道了不对称五氮齿大环铟和铅配合物的合成。并对其电子吸收光谱,荧光光谱,荧光量子产率及第一激发单重态寿命进行了测量.
关键词 不对称五氮齿金属配合物 电子吸收光谱 荧光量子产率 荧光寿命

Synthesis of Asymmetric Pentaazadentate Macrocyclic Indium and Lead Complexes and Their Photophysical Properties

Fengqi Guo Duoyuan Wang**
（Institute of photographic chemistry, Chinese Academy of Science Beijing 100101）

    Asymmetric pentaazadentate conjugated macrocyclic metal complexes containing 22 π-electrons are a kind of new metalloorganic materials with versatile potential application as photofunctional materials, such as photodynamic therapy agent, magnetic resonance imaging contrast agent and antisense agent materials [1]. In addition, these metal complexes can be used as optical limiting materials by using the optical nonlinearities [2] for the protection of optical sensor and human eyes from high intensity laser. Coordinating with different metal ions and/or altering the peripheral substituents of the complexes can regulate their properties. Therefore, more pentaazadentate metal complexes have been synthesized [8].

Ⅰ M = In3+    Ⅱ M = Pb2+

Figure 1. Structure of asymmetric pentaazadentate macrocyclic metal complexes

    In this paper, we report the synthesis and the photophysical properties for two new asymmetric pentaazadentate macrocyclic complexes with indium and lead ions (Fig.1). This will provide new materials for potential application of optical limiting.

    The ligand, 4,5,9,24-tetraethyl-16-carboxyl-10,23-dimethyl-13,20,25,26,27-pentaazapenta-cyclo[20,2·1·13,6·18,11·014,19] heptacoso-2, 4,6,8,10,12(21),14,16,18,20,22,24-dodecene (APPC-COOH), was prepared by acid catalytic 1:1 schiff base condensation reaction of 3,4-diamino-phenyl formic acid with 2,5-bis[(3-ethyl-5-formyl-4-methylpyrrol-2yl)methyl]-3,4-diethylpyrrole[3]. The macrocyclic ligand (APPC-COOH), trichloroindium and triethylamine were dissolved in a mixture solution of methanol (33%) and chloroform (67%) and heated at certain reflux temperature (70℃) under pure oxygen bubbling for nine hours. And then the reaction solution was gradually cooled to room temperature and the solvent was removed under reduced pressure. The product was purified by column chromatography through a hydrophobic silica gel (treated with the [(CH3)3Si]2NH ) using mixture solvent of chloroform containing a certain a mount of methanol (0%～5% V/V) as the eluviating agent. The deep green color elute was collected and the solvent was removed. The refined product was obtained (yield 85%) as complexⅠ.

    Complex Ⅱ was also obtained according to the similar procedure, except that the time of reaction was five hours only. The yield of complex Ⅱ was 86%.

    In course of the synthesis, at least a portion of these materials consist of six-coordinated complexes, in which benzimidazole (BzIm) coordinated on the perpendicular axis [6], it is very difficult to detach this material from the main product. The result has been tested by the element analysis data.

    The data of the structure characterization for complexes Ⅰ and Ⅱ are as follows:

    [(APPC-COOH)In]Cl2( Ⅰ ): Anal.Calcd.for C33 H33N5O2In·Cl2·0.3C8H6N: C: 56.50%, H: 4.60%, N: 9.90%. Found: C: 56.40%, H: 4.50%, N: 9.30%; λmax(ε/mol-1·L·cm-1): 333.3 ( 1.14×104), 440.2 (1.83×104), 760.3 nm (5.95×103); υmax(KBr): 2960, 1607, 1381, 1259, 1099, 966, 784 cm-1. MS FAB: 647(M+).

    [(APPC-COOH)Pb]Cl ( Ⅱ ): Anal.Caled.: C33 H33N5O2PbCl? 0.2C8H6N: C: 52.10%, H: 4.29%, N: 9.13%. Found: C: 52.00% , H: 4.73%, N: 8.85%; λmax(ε/mol-1·L·cm-1): 335.6 (1.93×104), 426.4 (1.69× 104), 750.5 nm (3.81×103); υmax(KBr): 2861, 1606, 1395, 1260, 1102, 966, 781cm-1; MS FAB: 740(M+).

    The absorption spectra were determined with 1cm×1cm-quartz cuvette on Hittachi 557 UV-VIS spectrophotometer. The electronic absorption spectra of asymmetric pentaazadentate macrocyclic indium and lead complexes in methanol contain the Q and Soret bands, in which the Q band split to Q (0, 0) and Q (1, 0) bands and the 0-0 π-electron transition appear at 760 nm (ε= 5.59× 103 mol-1 ·L·cm-1) and 750.5 nm (ε= 3.81×103 mol-1·L·cm-1) respectively. The soret bands appear at 440(1.83×104 mol-1 ·L·cm-1) and 435 nm (1.93×104 mol-1 ·L·cm-1). In addition, there is a N band at 320nm. The linear molar extinction coefficients between 500～700 nm are also of 103 order magnitudes. The ground state absorption cross sections (σg) of Q bands 2.28×10-17 cm2 for Ⅰ and 1.46×10-17 cm2 for Ⅱ are calculated according to the equation[5]ε=10-3σN0/ln10, where N0 is Avogadro constant. The oscillator intensities ( f ) for the Q and the Soret band of complex Ⅰ are 0.02 and 0.25 respectively. It appears that the transition probability of S0→S2 is much larger than that of S0→S1 transition. Similar result is also obtained for complex Ⅱ.

    Table 1 list the data of the maximum absorption peaks of the 0-0 transitions for complexes Ⅰ and Ⅱ in several solvents with different polarity ET(30). The results show that a blue shift of the 0-0 transition, so-called minus solvatochromism, occurs with the increasing of the solvent polarity. This demonstrates that the solvent molecules have stronger interaction with the complex molecules in the ground state to form a lower energy ground state species during the π→π* transition. For comparison, we measured the absorption spectrum of complex Ⅰ in SDS micelle, in which the Q band appeared at λmax 773.4 nm, which was similar to that of obtained in the nonpolar solvent. This shows that H-aggregation in the strong polar solvents has occurred, leading to a large blue shift for two complexes.

Table 1. Minus solvatochromism in polar solvents for pentaazadentate indium and lead complexes.
Solvent ethanol acetone dichloromethane chloroform benzene
ET(30) / kJ·mol-1 216.9 176.40 171.8 163.4 131.7
Ⅰ( Q band/nm ) 761 761 770 774 779
Ⅱ( Q band/nm ) 745 744 748 750 754

    The fluorescence spectra were determined with 1cm×1cm-quartz cuvettes on Hittachi 850 fluorescence spectrophotometer. The quantum yields Фf relative to ZnTPP[4](Фf = 0.03) were determined using a degassed dilute solution with an absorbance about 0.1 under the excitation wavelength of 420nm. After calibrating of the fluorescence spectra beyond 800 nm, the Фf was calculated. The fluorescence lifetimes were measured with the single photon counting technique on a Horibe NAES-1100 time-resolved fluorescence spectrophotometer (with the accuracy ≤0.2 ns). All solutions of the complexes with ～×10-5mol/L were deoxygenated by bubbling with high pure nitrogen over 20 min before measurement. Lifetime analysis was made with the deconvolution program and the emission decay via a single exponential mode at room temperature. The lifetimes are all less than 1ns and the Chi-Square (square root error) is less than 1.40.

    The values of the fluorescence peaks λmax, the lowest energies of the first excited singlet state Es, the fluorescence quantum yields Фf and the lifetime of the first excited singlet state τf with their nonradiation as well as radiation rate constants are listed in Table 2.

Table 2. The properties of the excited state of complex Ⅰ and Ⅱ

Complex λmax/nm Es/kJ· mol-1 Фf(×10-3) τf/ns kr/s-1(×105) knr/s-1(×109)
Ⅰ 798a 155.32a 2.14a 0.977a 21.9 1.02
Ⅱ 768b 　 0.18b 0.914b 2.00 1.09

a in methanol b In ethanol

    The results show that the fluorescence spectra appear at near-IR region and have a red shift beyond 150～200 nm compared with the tetraazadentate porphyrin complexes. The energy of the first excited singlet state decrease to about 155 kJ/mol. It implies that these molecules may be easily excited by absorption of lower energy photons.

    In addition, Their lifetimes of the first singlet excited state are very short, which is coincident with the lower fluorescence quantum yields. There are two reasons, one of them is the carboxyl hydrogen-bonding interaction, which promotes the nonradiation transition, and the other is the existence of the heavy atom effect of In3+ and Pb2+. So that the radiation rates constants are much smaller than that of the nonradiation, which makes the excited molecules decay predominately via nonradiation processes.

    The two new pentaazadentate macrocyclic indium and lead complexes have shown an extended optical window 420～760 nm between the Soret and Q band in the visible absorption spectra. The ε values at 532 nm are also near ～103 (mol-1·L·cm-1) which implies that this kind of molecules are of large absorption cross sections at 532nm in the ground state, which is larger than that of the C60[7], it makes these complexes possible to be good materials with lower optical limiting threshold for the potential application of optical limiter.

    Acknowledgment This project (NO.29682001 and NO.29832030) was supported by National Natural Science Foundation of China. Thanks Virginia Polytechnic Institute and State University Prof. R.O.Claus and Dr. Yanjing Liu for giving InCl3 and PbCl2.　

References
[1] Sun wenfang, Wang Duoyuan. Photographic science and photochemistry, 1996, 14(2):150
[2] Duoyuan Wang, Wenfang Sun, etc. MRS Meeting, March, 1997, California.P.316
[3] Sun Wenfang, Wang Duoyuan. Chin.Chem.Lett., 1993, 4(3): 225
[4] Harriman A., Porter G., Searle N., J.Chem.Soc.Fara.Trans.Ⅱ .1979, 75(11):1515
[5] T.H.Wei, D.J.Hagan, M.J.Sence, etc., Appl.Phy., 1992, 54(B):46
[6] J.L.Sessler, G.W.Hemmi, Toshiaki Murai. USA patent [4935498], 1990.
[7] Nan Kost, Lee Tutt, and M.Klein, et al., Opt.Lett., 1993, 18(5):334
[8] J.L.Sessler, Toshiaki Murai, and Gregory Hemmi, Inorg. Chem. 1989, 28:3390

**To whom correspondence should be addressed.
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