FULL PAPER Impact of position of electron withdrawing cyano groups on nonlinear optical properties of centrosymmetric donor- p-acceptor system Ran Hee Kim 1 | Jin Sun Park 1 | Kwang-Sup Lee 1 | Karin Zojer 2 | Jean-Luc Br  edas 3 1 Department of Polymer Science & Engineering, Hannam University, 1646 Yuseong-daero, Yusung-Ku, Daejeon 34054, Korea 2 Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, Graz 8010, Austria 3 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332 Correspondence Kwang-Sup Lee, Hannam University College of Life Science and Nano Technology, Department of Polymer Science & Engi- neering, 1646, Yuseong-daero, Yusung-Ku, Daejeon, South Korea 306-791. Email: kslee@hnu.kr Funding information MEST (NRF), Grant/Award Number: 2016R1A2B4008473; Korean Government, Grant/Award Number: KRF-2005-213- C00025 Abstract Two symmetrically substituted phenylenevinylene D-A-D 0 -A-D type siblings, (2Z,2 0 Z)-2,2 0 -(2,5- dimethoxy-1,4-phenylene)bis(3-(4-(dimethylamino)phenyl)acrylonitrile) ("-dscn) and (2Z,2 0 Z)-3,3 0 - (2,5-dimethoxy-1,4-phenylene)bis(2-(4-(dimethylamino)phenyl)acrylonitrile) (#-dscn), are prepared. We investigate the effect of different but symmetrical location of these cyano groups in vinylene bridges on the 1-photon and 2-photon absorption behaviors. We report that the closeness of CN group on the vinyl group to the central phenyl ring in "-dscn induces an intramolecular geometric distortion between the central phenyl ring and vinylene group, preventing the effective p-conjugation length in ground and excited states. Thus, the transition energy that is observed in 1-photon absorption and fluorescence is larger in "-dscn than in #-dscn. This leads to a different intramolecular charge distribution, as a result of which the linear and nonlinear optical properties strongly depend on the position of acceptors. These results are theoretically unraveled in terms of charge transfer pathways, charge distribution, and charge distribution differences on transition. KEYWORDS charge redistribution, geometry distortion, position of cyano group, quadrupolar, 2-photon absorption 1 | INTRODUCTION Interest in developing organic 2-photon absorbing materials with large nonlinear optical probability has been growing as the demonstration its potential applications in optoelectronics and microelectronic mechanical engineering such as 3D microfabrication, 3D data storage, optical power limiting, and deep penetration photodynamic therapy. [1–5] When an intense beam was focused on a material, the light intensity is high at the focal point and quadratically decrease going away from it. Therefore, the 2-photon absorption (TPA) probability of the material decrease steeply as the distance from the focused spot increases (z 24 ). Additionally, the wavelength of 2-photon excitation process is almost twice longer than that of 1- photon absorption. These intrinsic features of 2-photon absorbing process provide the advantages for those frontier technologies. For example, in photodynamic therapy the employment of longer wavelength of TPA, for which linear absorption is negligible, than the linear absorption process results in the deeper penetration and the less scattering in the media. For 3D microfabrication, the quadratic dependence of the 2-photon excitation probability on the incident beam endows a way to improve the 3D spatial resolution and to realize 3D complex structures in 1 simple picturing process. For those applications, highly sensitive 2-photon excitable chromophores are in huge demand. Thus, considerable effort has been concentrated to develop chromophores with large TPA activities, combined with other molecular properties like photostability, thermostability, and excitation wavelength for given applications. There has been systematic study of structure-property relationships for 2-photon absorbing materials. Various types of TPA chromophores have been explored so far such as dipolar (D-p-A), [6–8] quadrupolar (D-p-D or A-p-A), [9–12] octupolar, [12,13] Int J Quantum Chem. 2017;e25441. https://doi.org/10.1002/qua.25441 http://q-chem.org V C 2017 Wiley Periodicals, Inc. | 1 of 12 Received: 5 April 2017 | Revised: 23 June 2017 | Accepted: 13 July 2017 DOI: 10.1002/qua.25441