14988 J. Phys. Chem. 1995, 99, zyxwvu 14988-14991 Third Harmonic Generation Spectroscopy of Boron Subphthalocyanine Maria A. Diaz-Garcia and Fernando Agull6-L6pez* Dpto. Fisica de Materiales C-N, Universidad Autbnoma de Madrid, Cantoblanco, Madrid-28049, Spain Angela Sastre and Tomas Torres* Dpto. Quimica Orgcinica zyxwvutsrq C-I, Universidad Autbnoma de Madrid, Cantoblanco, Madrid-28049, Spain William E. Torruellas and George I. Stegeman C.R.E.O.L., University zyxwvuts of Central Florida, Orlando, Florida 32826 Received: March 30, 1995; In Final Form: July 13, 199P The dispersive behavior of the magnitude and phase of x3(-30: zyxwvu w,w,o,) of sublimated boron subphthalocyanine (SubPc) thin films has been investigated via third harmonic generation zyxw (THG) spectroscopy in the range 950-2000 nm. x3 values, three times bigger than those obtained for phthalocyanines in the same frequency range, have been measured. A four-level model, including the ground state and three excited states associated to bands observed in the linear absorption spectrum, has been successfully used to explain the nonlinear behavior of these compounds. Introduction Highly conjugated x-electron systems have been considered as the most suitable organic materials for third-order nonlinear optics.' Besides the conjugated polymers, metallorganic com- pounds are attracting growing interest due to their large third- order nonlinear optical responses.2 Metallophthalocyanines (MPcs),~ two-dimensional 18 n-elec- tron conjugated macrocycles, have been intensively investigated for third-order nonlinear applications4-I0 due to their highly delocalized x-electron system. The chemical flexibility of phthalocyanines facilitates the tailoring of their electro-optical parameters in a very broad range. For this reason, modifications of Pcs are usually made by incorporating a wide variety of central metal ions, by peripheral substitution of the macrocycle,' or by preparation of analogue^.^-"-'^ Interesting examples of Pc-related compounds are the so- called subphthalocyanines (SubPcs, l, Figure l).I4-l5These macrocyclic complexes are composed of three isoindole units containing boron inside. They show a delocalized 14 n-electron system similar to that present in PCS. Up to now the use of these compounds has been restricted to applications as intermediate materials for the synthesis of nonsymmetrical phthalocyanine^.'^-'^ Moreover, there are few reports published hitherto about the synthesis of SubPcs, probably due to their really difficult processes of puri- fication. I4-l6,*O A previous X-ray crystallographic studyI5 substantiated that SubPcs have a coned-shaped structure because of constraints arising from the coupling of the three isoindole units. However, spectral data reported by Kobayashi indicate that these molecules indeed have a strong aromaticity.20 Other attractive character- istics of SubPcs, besides their large n-electron conjugation, are their chemical (they support inorganic acids) and thermal (they can be sublimated at " H g at 350 "C) stability. These interesting features, as well as their singular geometry, prompted us to study their nonlinear optical properties in the context of our general project conceming the synthesis of Pcs and Pc analogues for nonlinear optical application^.^^-^^ @Abstract published in Aduance zyxwvutsrqpo ACS Abstracts, September zyxwvuts 15, 1995. 0022-365419512099- 14988$09.0010 1 Figure 1. Chemical structure of boron subphthalocyanine 1. In this paper we report on the preparation and purification of large amounts of the previously describedI4 SubPc 1 and on a detailed spectroscopic study of the magnitude and phase of the THG susceptibility x3(-3w: w,w,o,) of evaporated thin films of this compound. It should be noted that this susceptibility is purely electronic, being free from other contributions that affect the data obtained with alternative techniques such as degenerate four-wave mixing (DFWM)Io or z-~can.~ Experimental Section Synthesis and Characterization. Compound 1 was char- acterized by elemental analysis, IR, and W-visible spec- troscopies, mass spectrometry and nuclear magnetic resonance spectroscopy. The W-visible and infrared measurements were carried out on Perkin-Elmer model Lambda 6 and PU 9716 Philips spectrometers, respectively. The MS spectrum was determined on a MAT 900 (Finnigan MAT, GmbH, Bremen) instrument. The proton NMR spectrum was recorded with a Bruker wM-200-SY, 200 MHz spectrometer. The purity of the compound was determined on a Perkin Elmer Integral 4000 analytic high-performance liquid chromatographer Perkin Elmer Integral 4000 using toluene as mobile phase and a nucleosil 5-nitro column. Synthesis of the Subphthalocyanine 1. A suspension of 12.8 g (0.1 mol) of zyxwv dry phthalonitrile (recrystallized from methanol and dried in vacuum) in 12 mL of anhydrous l-chloronaphtha- lene was magnetically stirred and cooled at -78 "C, in a 100 mL three-neck round-bottomed flask equipped with a thermo- 0 1995 American Chemical Society