Journal of Photochemistry and Photobiology A: Chemistry 290 (2014) 38–42 Contents lists available at ScienceDirect Journal of Photochemistry and Photobiology A: Chemistry jo u r n al homep age: www.elsevier.com/locate/jphotochem Second- and third-order nonlinear optical properties of bis-chalcone derivatives M. Sai Kiran a , Benoy Anand b , S. Siva Sankara Sai b , G. Nageswara Rao a,∗ a Department of Chemistry, Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam, Andhra Pradesh 515134, India b Department of Physics, Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam, Andhra Pradesh 515134, India a r t i c l e i n f o Article history: Received 5 February 2014 Received in revised form 6 May 2014 Accepted 6 June 2014 Available online 14 June 2014 Keywords: D––A––D SHG Z-scan Two photon absorption Optical limiting a b s t r a c t Bis-chalcone derivatives: 2,5-bis(benzylidene)-cyclopentanone (CP-DBA), 2,5-bis(4-methoxy- benzylidene)-cyclopentanone (CP-POME), 2,5-bis(4-isopropyl-benzylidene)-cyclopentanone (CP-ISO) and 2,5-bis(cinnamylidene)-cyclopentanone (CP-CAL) are synthesized by Claisen–Schmidt reaction and characterized using, FT-IR, 1 H NMR, 13 C NMR, and mass spectroscopic techniques. The second- and third-order nonlinear optical properties of these samples are studied using second harmonic generation and nanosecond open-aperture Z-scan methods. CP-POME has shown a very high second harmonic generation (SHG) efficiency (5.3 times that of urea). These molecules reveal a strong third-order nonlinear absorption (NLA) that is of optical limiting type, due to their peculiar D––A––D structure that leads to high polarization of the delocalized electron cloud. CP-CAL exhibits highest NLA activity with a ˇ coefficient of 1 × 10 -10 m/W. Through numerical simulations, the mechanism of NLA is found to be a two-photon absorption process in the case of all the samples. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The development of nonlinear optical (NLO) molecules has attracted the spotlight of modern research in view of their impending applications in photonic technologies [1–3]. Organic compounds possessing conjugated  electron system connected to a donor (D) and an acceptor (A) have been receiving much attention for optical limiting (OL) applications. They possess high nonlin- earity coupled with ultra-fast response which are tunable through structural modification [4]. Chalcones, a class of organic materials, are attractive for their large SHG efficiencies [5,6]. In chalcone type organic molecules, the -electrons are delocalized all along the length of the molecule and are easily polarizable. To enhance the nonlinear absorption (NLA) in these organic molecules, researchers have developed numer- ous design strategies such as donor–acceptor–donor (D–A–D), acceptor–donor–acceptor (A–D–A) and donor–pi–donor (D––D) architectures [7,8]. Three essential components required for a high non-linear active organic molecule are a strong -electron donor (D), a polarizable -bridge, and a strong -electron acceptor (A). The key molecular features determining the structure of a highly ∗ Corresponding author. Tel.: +91 9492595462. E-mail addresses: gnageswararao@sssihl.edu.in, nageswar.rao@rediffmail.com (G. Nageswara Rao). active two-photon absorbing (2PA) chromophore are the extent of conjugation and the presence of charge transfer (-donor and - acceptor) groups to increase the charge transfer from end of the molecule to the centre [9–12]. In recent years, tremendous attention has been drawn towards chalcone derivatives as they have varied photonic applications. In addition, they are also used for the synthesis of flavonoids and for a number of biological activities [13–15]. In the present study, we report the synthesis, characterization, second harmonic generation (SHG) applications and third order nonlinear 2PA properties of CP- DBA, CP-POME, CP-ISO and CP-CAL. 2. Experimental 2.1. Synthesis The above mentioned compounds were synthesized according to Claisen–Schmidt reaction [16]. To a stirred solution of sodium hydroxide (6.25 g) in 62.5 ml of water and 62.5 ml of ethanol at 298 K, one half of the previously prepared mixture of 0.25 mol of substituted aldehyde and 0.125 mol of cyclopentanone was added. After 15 min, the remaining solution was added and stirring was continued for further 45 min at 298 K. The precipitated product was filtered and washed with cold water, till the washings were free of alkali. The final products were recrystallized from hot methanol/ethanol. http://dx.doi.org/10.1016/j.jphotochem.2014.06.004 1010-6030/© 2014 Elsevier B.V. All rights reserved.