Porphyrin Dendrimers
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Porphyrin Dendrimers Flores-Rojas Guadalupe G.1, Martínez-Klimov Mark E., Morales-Saavedra Omar G.2, and Martínez-García Marcos 1,* 1
Instituto de Química, Universidad Nacional Autónoma de México, Cd. Universitaria, Circuito Exterior, Coyoacán, México D.F. C.P. 04510, Mexico. 2 Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, CCADET-UNAM, Circuito exterior S/N, Ciudad Universitaria, México D.F. C.P. 04510, México.
ABSTRACT Dendrons with a porphyrin core and π-conjugated dendron branches have been synthesized and characterized. The dendrons showed an all trans configuration. Cubic non-linear optical behavior of the styryl and porphyrin-containing dendrimers was tested via Z-Scan measurements in spin-coated film samples. Keywords: ! INTRODUCTION The design and synthesis of π-conjugated dendrimers has been explored extensively as active chemical components in a wide range of electronic and optoelectronic devices1. Dendrimers have attracted much attention because of their excellent electroluminescent and electroconductive properties, the globular shape of dendrimers provides a large surface area that can be decorated with different chromophore species, thus resulting in a large absorption cross-section and enabling efficient capture of photons2. The nonlinear optical (NLO) properties of several dendrimers have been published3. Here, we report the synthesis and cubic NLO behavior of first and second-generation dendrimers with π-conjugated branches and a porphyrin core. EXPERIMENT Materials and equipments Solvents and reagents were purchased as reagent grade and used without further purification. Acetone was distilled over calcium chloride. 1H- and 13C-NMR were recorded on a Varian-Unity-300 MHz with tetramethylsilane (TMS) as an internal reference. Infrared (IR) spectra were measured on a spectrophotometer Nicolet FTSSX. Elemental analysis was determined by Galbraith Laboratories Inc. (Knoxville, TN, USA). Electrospray mass spectra were taken on a Bruker Daltonic, Esquire 6000.
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Synthesis of dendrimers A mixture of the respective dendron 1 or 2 (1 mmol), potassium carbonate (21.2 mmol), and 18-crown-6 (0.56 g, 2.12 mmol) in dry acetone (80 mL) was heated to reflux and stirred vigorously in nitrogen atmosphere for 20 min. porphyrin 3 (0.125 mmol) dissolved in dry acetone (40 mL) were added dropwise and the reaction was continued for 7 days. The mixture was cooled and the precipitate was filtered. The filtrate was evaporated to dryness and the dendrimers were purified. Dendrimer 4. Yield 0.66 g (55 %), purple solid, mp 226 oC, UV–vis CH2Cl2 (nm): 231, 302, 422, 454, 518, 556, 595, 651, 694. IR (KBr, cm-1): 3434, 2056, 3026, 2922, 2857, 1655, 1636, 1600, 1500, 1453, 1406, 1379, 1284, 1235, 1174, 1111, 1068, 1015, 987, 960. 1H NMR (300 MHz, CDCl3) δH (ppm): -2.68 (s, 2H), 5.3 (s, 8H), 7.25 (s, 40H), 7.28 (d, 2H, J=1.5 Hz), 7.34 (d, 8H, J= 9 Hz), 7.35 (s, 4H,), 7.38 (d, 8H, J= 14.7 Hz), 7.41 (d, 8H, J= 14.7 Hz), 7.43 (t, 2H, J= 1.5 Hz),
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