Nonlinear optical characterizations of dibenzoylmethane in solution Yashashchandra Dwivedi, Gabriel Tamashiro, Leonardo De Boni n , Se ´ rgio C. Zilio Instituto de Fı ´sica de S ~ ao Carlos, Universidade de S ~ ao Paulo, Caixa Postal 369, 13560-970 S ~ ao Carlos, SP, Brazil article info Article history: Received 9 October 2012 Received in revised form 22 November 2012 Accepted 23 November 2012 Available online 10 December 2012 Keywords: Femtosecond Z-scan Two-photon absorption cross-section First hyperpolarizability Hyper-Rayleigh scattering abstract This work reports on the two-photon absorption (2PA) cross-section and first hyperpolarizability of dibenzoylmethane solutions using femtosecond Z-scan and hyper-Rayleigh scattering techniques. The 2PA spectrum, spanning the wavelength range from 460 to 740 nm, presents a band centered at 510 nm, with a cross-section value estimated as 37 GM at this wavelength. Owing to the molecular symmetry, this band is not observed in the linear absorption spectrum. The sum-over-state approach was adopted to evaluate various spectroscopic parameters. Experimental and theoretical values of the first hyperpolarizability values were estimated in ethanol and DMSO solutions. & 2012 Elsevier B.V. All rights reserved. 1. Introduction The dibenzoylmethane (DBM) molecule has attracted consider- able attention because of its application in a variety of fields, especially in biomedicine and display devices [1]. DBM is a member of naturally occurring compounds that belong to the b-diketone family, exhibiting enol and kito tautomeric forms. Quantum che- mical calculation of electronic spectra of both forms were already studied in the past [2,3]. It was shown to inhibit the growth of various types of cancer cells in vitro and to prevent the carcinogen- esis in various animal models. In particular, it inhibits the carcino- genesis of mammary glands induced by the well-known carcinogen 7,12-dimethylbenz[a]anthrance, both in vivo and in vitro [4–6]. When compared to curcumin, which also belongs to the b-diketone family, DBM lacks the phenolic hydroxyl groups and the reducible unsaturated alkyl groups. As a result of these structural modifica- tions, dibenzoylmethane shows very small antioxidant ability in vitro and is well absorbed and distributed in tissues in vivo [7,8]. Marin et al. [9] already discussed the photochemical and photophysical properties of DBM derivatives within proteins. How- ever, the application of this molecule in photodynamics therapy is limited by its absorption in the ultraviolet (UV) region only, which is far from the ‘‘therapeutic window’’ region (between 600 and 800 nm), where biological tissues are relatively transparent. Hence, light cannot penetrate deeply into the tissues, thus limiting its application to superficial lesions. Additionally, the distribution of DBM inside the cell cannot be tracked by linear microscopy. One solution to this problem is to use a 2PA process, which is a well established technique used in applications such as: two-photon polymerization [10], three-dimensional optical data storage [11], fluorescence excitation microscopy [12], optical limiting [13] and two-photon photodynamic therapy [14]. Considering the abovementioned properties of the DBM mole- cule, it seems worth to investigate its nonlinear optical properties in detail. It possesses considerable planarity in the ground-state, suggesting good p-electron delocalization due to the ability of performing intramolecular charge transfer [15,16], thus acting as a push–pull compound. However, the nonlinear optical characteriza- tion of dibenzoylmethane in solutions was not reported, except for the strong second harmonic generation observed by Li et al. in lanthanide complexes containing DBM [17] and the calculation of the first hyperpolarizability performed by Wostyn et al. in lantha- nate complexes with DBM [18]. The present work reports on the nonlinear optical characteriza- tion of the DBM molecule in solutions. The 2PA cross-section and the first hyperpolarizability were determined through Z-scan and hyper Rayleigh scattering measurements. Theoretical calculations of the hyperpolarizability were also carried out in the gas phase and with solvents for comparison with the experimental data. 2. Experimental Dibenzoylmethane of analytical purity was purchased from Sigma-Aldrich. Spectroscopic grade ethanol and dimethyl sulf- oxide (DMSO) were used as solvents. Solutions with different concentrations were prepared and ultrasonicated for 10 min before performing the experiments in order that the proper mixing and thermodynamic equilibrium could be established Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/optcom Optics Communications 0030-4018/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optcom.2012.11.065 n Corresponding author. E-mail address: deboni@ifsc.usp.br (L.D. Boni). Optics Communications 293 (2013) 119–124