This journal is © the Owner Societies 2016 Phys. Chem. Chem. Phys., 2016, 18, 21833--21842 | 21833 Cite this: Phys. Chem. Chem. Phys., 2016, 18, 21833 Solvent effects on static polarizability, static first hyperpolarizability and one- and two-photon absorption properties of functionalized triply twisted Mo ¨ bius annulenes: a DFT study† Md Mehboob Alam,‡* a Varun Kundi‡ b and Pompozhi Protasis Thankachan* b The present work aims to study solvent effects on the polarizability (a), static first hyperpolarizability (b) and one- and two-photon absorption (OPA and TPA) properties of a new class of molecules viz. triply twisted Mo ¨ bius annulenes, recently studied by us in vacuum phase [Kundi et al., Phys. Chem. Chem. Phys., 2015, 17, 6827]. We have employed linear and quadratic response theories within the framework of time- dependent density functional theory with the CAM-B3LYP functional and a cc-pVDZ basis set to calculate different parameters. The microscopic details of the said properties have been studied using a two-state model (2SM) approach, which performs very well in the case of b and TPA of the first excited state of all the systems. However for the second excited state, the 2SM results are far from those of response theory. In fact, in comparison to response theory, 2SM predicts an opposite trend for the TP activity of some of the model systems, indicating a significant contribution from the other higher excited states. The anomaly between the 2SM approach and response theory has been resolved by incorporating three states in the calculations. 1 Introduction The quest for efficient non-linear optical (NLO) materials has led to the exploration and design of a wide range of molecules. The motivation for the immense growth in this field comes from the potential applications of such materials in cutting- edge technologies like three-dimensional optical data storage, 1 photochromic switches, 2,3 fluorescence imaging, 4 two-photon optical power limiting, 5 multiphoton fabrication, 6 two-photon lithography 7 and photodynamic therapy 8–10 to mention a few. As appreciated by the European Commission and European Science Foundation, photonics play a lead role as one of the key enabling technologies in socio-economic developments in this century. 11,12 In this context, it is worth mentioning that their technological growth is equally supported by corresponding theoretical studies in terms of providing correct prediction and interpretation of experimental observations, e.g. those from UV-visible, 13,14 ro-vibrational, 15 magnetic resonance, 16–18 and non-linear spectroscopy. 19–21 The first step towards the design of desirable NLO materials is performed nowadays using state-of-the-art quantum chemical calculations to save both time and chemicals. This step provides a clear under- standing of the mechanism of the process prior to the synthesis of the desired NLO materials and helps to look for other interesting properties and corresponding structure–property relationships. 22–24 In this work we are interested in properties like static first hyperpolarizability (b) and two-photon absorption (TPA) along with static polarizability and one-photon absorption (OPA). One of the successful theoretical methods for studying TPA process is the full sum-over-states (SOS) approach. 25 However, even for medium sized molecules this is computationally expensive. Furthermore, the involvement of all the eigenstates of the molecule makes it difficult to interpret the corresponding results. Another approach for studying absorption/emission processes is response theory, 26–31 where the exact SOS value is implicitly obtained by calculating the residues and poles of the response functions, which requires the solution of a set of linear matrix equations. Response theory provides experimentally comparable results for both the static and dynamic properties. The transition dipole moment vectors (TDMVs) obtained from response theory can also be used to study the effect of dipole alignment 32–35 as well as the corresponding structure–property relationships. 32–42 In principle, one can obtain all TDMVs from the residues of a Laboratoire de Chimie Quantique, Institute de Chimie, CNRS/Universite ´ de Strasbourg, 1 rue Blaise Pascal, 67000 Strasbourg, France. E-mail: malam@unistra.fr; Tel: +33 75 31 03 065 b Theoretical Chemistry Lab, Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee-247667, Uttarakhand, India. E-mail: thankachan1950@gmail.com † Electronic supplementary information (ESI) available. See DOI: 10.1039/c6cp02732f ‡ These authors have contributed equally. Received 24th April 2016, Accepted 16th June 2016 DOI: 10.1039/c6cp02732f www.rsc.org/pccp PCCP PAPER Published on 05 July 2016. Downloaded by Indian Institute of Technology Roorkee on 13/08/2016 05:32:18. View Article Online View Journal | View Issue