J. Phys. Chem. 1994,98, 44954497
449s
Third-Order Nonlinear Optical Properties of Soluble Metallotriazolohemiprphyrazines Maria A. Dlaz-Garcia,+Isabelle Ledoux,s Fernando Ferniindez-LBzaro,*Angela Sastre,* Tomiis Torres,***Fernando Agull6-Mpez,’qt and Joseph Zyss*+S Departamento Fisica de Materiales C-IV and Quimica Orghnica C-I, Universidad Autbnoma de Madrid, 28049 Madrid, Spain, and FRANCE TELECOM, CNET Paris- B Dhpartement d’Electronique Quantique et Molbculaire, 196, Av. Henri Ravera, 92225 Bagneux. France Received: January 5, 1994; In Final Form: March 9, 1994”
Soluble lipophilic-substituted metallotriazolohemiporphyrazines (MThp), structurally related to metallophthalocyanines, have been synthesized for the first time. The real part of their third-order molecular hyperpolarizabilities y has been determined by third-harmonic generation in chloroform solutions. Two fundamental wavelengths (A = 1340 and 1904 nm) have been used to investigate the dispersive behavior of y. Values between 10-34and esu have been found, depending on excitation wavelength and metal substitution. In fact, unfilled d-shell transition ions markedly enhance the molecular hyperpolarizability, the highest values being measured for the Fe*+- and Co2+-substituted molecules.
Introduction
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Organic molecules with extensively delocalized *-conjugated systems are potentially useful for application as third-order nonlinear optical (NLO) materials.’-3 On the other hand, organometalliccompounds4offer additional features to optimize the nonlinear response. Besides the *--A* transitions of the conjugated system, they present charge-transfer transitions from ligand to metal (LMCT) and from metal to ligand (MLCT), as well as metal to metal transitions, which provide enhanced possibilities for tailoring the ~ ( 3 susceptibilities. ) In particular, the two-dimensional *-conjugated metallophthalocyanine~S~3 show large third-order nonlinearities, which are markedly dependent on metal substitution. Unfortunately, most studies on these and related c0mpounds1~l~ have been performed on thin films, where structure and order parameters are not well-defined, so that the third-order microscopic nonlinear optical response cannot be reliably inferred from the macroscopic one, contrary to the case of single crystals or solutions. This situation, together with the diversity of nonlinear techniques (and so involved mechanisms), haspreventedan adequateevaluationoftherelation between structure and nonlinear behavior. Therefore, additional work at a molecular level is needed for a better understanding of the third-order response of these metallomacrocycles. The most important advantages of the phthalocyanine-like compounds are their versatility and architectural flexibility5that allow the tailoring of the physicochemical parameters and, moreover, the possibility to carry out studieson structureproperty relationships. Recently, the preparation and characterization of unsubstituted metallotriazolohemiporphyrazineshave been des ~ r i b e d . ~ 8These J ~ compounds are formal derivatives of phthalocyanines by replacement of two opposite isoindole rings by two 1,2,4-triazole subunits. The electronic structure of these hemiporphyrazines can be altered through ligand (peripheral substitution) and metal modification in a number of interesting ways. Metallotriazolohemiporphyrazinesare unsoluble in all common organic solvents, thus preventing the study of their optical properties in solution. However, we have shown that the introduction of peripheral lipophilicsubstituentson the two triazole rings and/or on the isoindole moieties increases drastically the
* To whom correspondence should be addressed.
t Departamento FIsica de Materiales C-IV, Universidad Aut6noma de
Madrid. t Qufmica Organica C-I, Universidad Autbnoma de Madrid. 1 FRANCE TELECOM. a Abstract published in Aduunce ACS Abstrucrs, April 15, 1994.
0022-3654/94/2098-4495$04.50/0
N-N‘
/I
.\
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N+~//’N
@
NYQYN N
N
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MThp M = Mn(ll) M = Fe(ll) M = Co(ll) M = Ni(ll) M = Cu(ll) M = Zn(ll)
Figure 1. Chemical structure of triazolohemiporphyrazines.
solubility of the compounds.18 This had led to the preparation of a number of lipophilic substituted metallotriazolohemiporphyrazines, whose structure is shown in Figure 1. The real part y(30;w,w,w) of the third-order hyperpolarizability has been determined for all these molecules from third-harmonicgeneration (THG) experiments on chloroform solutions. Contrary to other techniques (e.g., four-wave mixing), only electronic mechanisms are involved in the nonlinear response. To investigate resonant effects, two fundamental wavelengths have been used, 1340 and 1904 nm. As a main outcome of the data, the role of unfilled d-shellsin enhancingthe electronicy has been clearlyascertained. Although a detailed quantitative understanding is not possible at this stage, the data are discussed in light of the available information on structurally-related systems. Experimental Section The compoundswere characterized systematically by elemental analysis, IR and UV-vis spectroscopies, fast atom bombardment (FAB)-mass spectrometry, and also nuclear magnetic resonance in the case of diamagnetic complexes. The UV-vis and infrared measurements were carried out on Perkin-Elmer Model Lambda 6 and PU 9716 Philips spectrometers, respectively. FAB-MS spectra were determined on a MAT 900 (Finnigan MAT, GmbH, Bremen) instrument. Proton NMR spectra were recorded with a Bruker WM-200-SY 200-MHz spectrometer. The THG experiments have been performed in chloroform solutions, the third harmonic response being measured as a function of the concentration, using the Maker fringe technique in the wedge configuration.20 Measurements were made at fundamental wavelengths of 1340 and 1904 nm. The first one is emitted by a Q-switched Nd3+:YAG laser with 60-11s pulse 0 1994 American Chemical Society
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The Journal of Physical Chemistry, Vol. 98, No. 17, 1994
Letters
duration, while the second one is provided by a high-pressure hydrogen cell pumped by a Q-switched Nd3+:YAG laser (pulse duration 20 ns), leading to a Raman-shifted first Stokes radiation at 1904 nm. Synthesis of 8,20-Didodecyl-5,24:12,17-diimino-7,10:19,22dinitrilo-8HY20H-and 8,21-Didodecyl-5,24:lZ,17-diimino-7,10 19,22-dinitrilo-8H,Zl H-dibenzoLf,p] [I ,2,4,9,11 ,I 2,14,19]octaaza~ycloei~osinate(2-)-N2~,N~~,N~~,N~~ Metal(IZ) (MThp). General Procedure. A mixture of H2Thpl8 (100 mg, 0.13 mmol) and the corresponding metal(I1) acetate (chloride in the case of iron) (0.15 mmol) in 2-ethoxyethanol (15 mL) was heated at reflux temperature for 24 h. The reaction was monitored by IR 0 until disappearance of the starting material. After cooling the 200 400 600 800 mixture was filtered, and the solid was successively washed with WAVELENGTH (nm) 2-ethoxyethanol, triturated with hot methanol, and dried. All melting points are above 200 OC. Figure 2. Optical electronic spectra of HZThp (continuous line) and CoThp (dashed line). MnThp IR (KBr) (cm-I): 2920 (s), 2850, 1620 (w), 1580 (s, C-N), 1510,1470 (w), 1430 (w), 1355,1300, 1190 (w), 1100 1 (w), 1070, 760, 700, 650 (w). UV-vis X,/nm (a/dm3 mol-' cm-I) (CHCl3) 242 (4.7), 290 (sh), 350 (sh), 368 (4.6), 385 0.9 0.8 (4.6), 460 (sh), 505 (3.1), 545 (3.0), 590 (2.9), and 665 (2.6). FAB-MS (m-NBA) (m/z): 809 (M+), 810 [(M H)+]. FeThp IR (KBr) (cm-I): 2920 (s), 2850, 1620 (w), 1580 (s, C=N), 1510,1470,1360,1300,1190(w),1100,1080,760,710, 665 (w). UV-vis X,,/nm (€/dm3 mol-' cm-l) (CHC13) 242(4.7), 270 (sh), 335 (4.4), 345 (4.4), 365 (4.3), 385 (4.2), 420 (sh), 480 (sh), 595 (2.8), and 655 (3.3). FAB-MS (m-NBA) (mlz): 811 [(M+H)+]. CoThpIR(KBr) (cm-I): 292OY2850,1630(sh),159O(s,C=N), 1580 (sh), 1510,1470,1380, 1360,1310,1290 (w), 1100,1080 (w), 785 (w), 760 (s), 720 (w), 700. UV-vis X,,/nm (t/dm3 CELL DISPLACEMBNT (Microns) mol-' cm-I) (CHC13) 242 (4.7), 270 (sh), 290 (4.6), 340 (sh), 352 Figure 3. Harmonic intensity as a function of cell translation (Maker (4.6), 365 (4.6), 390 (sh), 435 (4.2), 475 (3.9), 520 (3.6), 475 fringes for a chloroform solution of FeThp (5 X 10-4 wt %); (dots) (3.9), 520 (3.6), 550 (3.5), 610 (3.5), 640 (3.6), and 665 (3.7). experimental values; (continuous line) best fit. FAB-MS (m-NBA) (m/z): 814 [(M+H)+]. NiThp IR (KBr) (cm-I): 2920,2850,1630 (w), 1600 (s, C=N), Optical spectra of the free and the Co2+complexes (HzThp 1590 (sh), 1520, 1470, 1380, 1320, 1290 (w), 1200 (w), 1100, and CoThp) are displayed in Figure 2 as an example of the 1060 (w), 780 (w), 760 (s), 720 (w), 700. UV-vis X,,,/nm (e/ observed behavior. The spectrum of HzThp is dominated by dm3 mol-' cm-1) (CHC13) 242 (5.1), 285 (sh), 335 (4.6), 358 strong absorption bands in the near-UV between 330 and 385 (4.5), 365 (4.5), 380 (4.5), 400 (4.5), 425 (4.6), 475 (2.9), 515 nm, together with weak absorptions in the UV-vis region at 410(3.0), 555 (3.0), 605 (2.9), and 665 (2.5); FAB-MS (m-NBA) 590 nm. They are associated tor
