Push-pull thiophene chromophores for electro-optic applications: from 1D linear to β-branched structures

• Published in: Physical chemistry chemical physics : PCCP 2020-01, Vol.22 (4), p.2283-2294
• Main Authors: Rothe, Christian, Neusser, David, Hoppe, Niklas, Dirnberger, Klaus, Vogel, Wolfgang, Gámez-Valenzuela, Sergio, López Navarrete, Juan T, Villacampa, Belén, Berroth, Manfred, Ruiz Delgado, M. Carmen, Ludwigs, Sabine
• Format: Article
• Language: English
• Subjects: Chromophores; Comparative studies; Design modifications; Linear systems; Mathematical analysis; Nonlinear optics; Optical materials; Optical properties; Optics; Organic chemistry; Thermal stability; Thermodynamic properties; Thiophenes
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c9cp05640h

We report the synthesis and characterization of a novel series of push-pull chromophores bearing 1D linear and β-branched thiophenes as π-conjugated spacers between a 2,2,4,7-tetramethyl-1,2,3,4-tetrahydroquinoline electron donor unit and dicyano- and tricyanovinylene electron acceptor groups. The effect of the introduction of β-thiophenes on the linear and nonlinear (NLO) optical properties as well as electrochemical and thermal data is studied in detail by performing a comparative study between the branched and 1D linear systems. In addition, a parallel DFT computational study is used to evaluate structure-property relationships. The non-linear optical behavior of the molecules both in solution and in solid state as electro-optic (EO) films using a guest-host approach shows very promising performance for electro-optic applications with high molecular first hyperpolarizabilities ( μβ ) of 4840 × 10 −48 esu and electro-optic coefficients r 33 reaching 650 pm V −1 . One highlight is that the electro-optic films of the β-branched chromophores are superior in terms of thermal stability in device operation as measured by a transmissive modified reflective Teng-Man method. This work provides guidelines for the design of improved electro-optic materials including β-branched chromophores which could be useful for practical EO applications, where both enhanced β and r 33 values together with chemical and thermal stability are necessary. This study demonstrates that β-branched thiophenes exhibit improved NLO properties and thermal stability for electro-optic applications compared to 1D linear systems.