NLO properties of ester containing fluorescent carbazole based styryl dyes e Consolidated spectroscopic and DFT approach Manali Rajeshirke, Nagaiyan Sekar * Department of Dyestuff Technology, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai, 400 019, India article info Article history: Received 30 November 2017 Received in revised form 15 December 2017 Accepted 17 December 2017 Keywords: Carbazole Two photon absorption cross-section s 2PA CAM-B3LYP BHandHLYP Bond length alternation (BLA) Bond order alternation (BOA) Hyperpolarizability Mulliken-Hush charge transfer abstract The linear and nonlinear optical (NLO) properties of new fluorescent styryl dyes based on anchoring ester containing carbazole as donor appended to different acceptor groups to have a conjugated p-system with push-pull geometry are studied. The NLO properties have been determined using solvatochromic and computational methods. Three different TD-DFT functional are used namely, B3LYP, BHandHLYP, and CAM-B3LYP, with aim of elucidating better functional for NLOphores. Further, the two photon properties (s 2PA ) have been described theoretically by two level model considering the dipole moment difference between the ground and the final electronic states and bypassing the intermediated resonance state. The compounds with a high charge transfer from the acceptor group to the carbazole ring have relatively high two-photon absorption cross-sections (60e317 GM). The linear polarizability (a CT ), first order hyperpolarizability (b) and second order hyperpolarizability (ɣ) for 4c dye was the highest among the studied dyes which is attributed to the lesser energy gap evident by both the methods. But in contrary, the s 2PA cross-section value was low for dye 4c which is due to the presence of freely rotatable twisted phenyl ring in the conjugation path, pulling the electron density towards itself and thus lead to decrease in s 2PA cross-section. Structure-property relationship is better understood by the correlation of bond length alternation/bond order alternation (BLA/BOA) with NLO properties of dyes. Thus by simple sol- vatochromic method and computational method, we have screened the carbazole styryls as NLO can- didates with good first order hyperpolarizability and good two photon cross-section. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Carbazole core serves as an excellent donor in D-p-A system because of its large p-electron conjugation and strong intra- molecular charge transfer (ICT) characteristics which even make them an excellent hole transporting material [1e5]. The Donor-p- Acceptor (D-p-A) push-pull chromophores associated with carba- zole moiety have been investigated largely [3,6e9] in recent years for their use in electroluminescent [7], photoluminescent [10], organic nonlinear optical (NLO) materials, organic light emitting devices (OLED) [11]. The organic NLOphoric materials have been the objects of current interest over the inorganic materials like lithium niobate in optoelectronic devices because of the fast response time compared to inorganic NLO materials as the polar- izability in organic NLOphores is of purely electronic origin [12e14]. The carbazole shows good photophysical properties [15] and easy functionalization of the carbazole core at 3, 6 and 9 positions by covalently linking to other molecules make them applicable in various potential applications [16]. Thus the push-pull chromo- phores could be tailor-made for better NLO properties by modu- lating the D-p-A system thereby perturbing the p-electron delocalization of the local excited state attained by absorption of photons leading to intramolecular charge transfer (ICT) [17 , 18]. The nature of N-substituent in carbazole influences greatly the fluorescence. Fluorescence usually occurs in dilute solution. The emission is usually weak or quenched in condensed phase. This can be overcome by introduction of alkyl chain which suppresses the association or recombination of dyes and formation of excimers [19]. The N-alkyl carbazole have excellent thermal stability and show good electro-optical properties [20,21]. The presence of easy derivatizable ester group at the alkyl end make such carbazole chromophores applicable as derivatization reagents for pre- or post-column derivatization techniques in HPLC analysis of a variety of compounds [22]. The zinc and cadmium carbazolylacetato complexes show strong blue emissions as well as high thermal * Corresponding author. E-mail addresses: n.sekar@ictmumbai.edu.in, nethi.sekar@gmail.com (N. Sekar). Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat https://doi.org/10.1016/j.optmat.2017.12.035 0925-3467/© 2017 Elsevier B.V. All rights reserved. Optical Materials 76 (2018) 191e209