Modular synthesis of zwitterionic, xanthene bridged, low twist angle chromophores with high hyperpolarizability. Issue 20 (18th August 2022)

• Record Type: Journal Article
• Authors: Mohammad-Pour, Gavin S.; de Coene, Yovan; Wiratmo, Meryl; Maan, Aditya; Clays, Koen; Masunov, Artëm E.; Crawford, Kaitlyn E.
• Is Part Of: Materials advances. Volume 3:Issue 20(2022)
• Page Start: 7520
• Page End: 7530
• Publication Date: 2022-08-18
• Subjects: 620.11
• DOI: 10.1039/d2ma00721e
• Languages: English
• ISSNs: 2633-5409

Abstract

Abstract : Push–pull chromophores exhibit useful electro-optic (EO) properties that have the potential to significantly improve non-linear EO applications ranging from telecommunications to quantum informatics. Abstract : Push–pull chromophores exhibit useful electro-optic (EO) properties that have the potential to significantly improve non-linear EO applications ranging from telecommunications to quantum informatics. Compounds with large hyperpolarizability values ( β ) that are stable and have easily modifiable functional groups are needed to advance organic-based EO systems. In this report, theoretical and experimental methods were used to investigate the design, synthesis, and application of a new class of push–pull chromophores for their use as a guest in guest–host EO polymer composites intended for non-linear EO applications. The chromophores combine the known intramolecular charge transfer benefits of increasing electron localization among π-conjugated zwitterionic structures with the aim of enhancing their β without the necessity of large dihedral angles. The class of chromophores reported here include a xanthene unit between a dicyanomethanide donor and pyridinium accepter. This arrangement increases charge separation due to the central sp 3 hybridization and enables modular aliphatic substitutions while maintaining concise, high yielding synthetic steps. Chromophore design selection was guided by high-throughput quantum chemical Density Functional Theory calculations to predict β and dipole moment ( μ ) a priori . Out of 230 molecular candidates considered, we present the results for three chromophores: dicyano(9, 9-dibutyl-7-(1-(2-ethylhexyl)pyridin-1-ium-4-yl)-9 H -xanthen-2-yl)methanide (E1 ), dicyano(4-(9, 9-dibutyl-7-(1-2-ethylhexyl)pyridine-1-ium-4-yl)-9 H -xanthen-2-yl)methanide (E2a ), and (4-(9, 9-bis(2-ethylhexyl)-7-(1-(2-ethylhexyl)pyridine-1-ium-4-yl)-9 H -xanthen-2-yl)phenyl)dicyanomethanide (E2b ). While bulk EO coefficients were low (<2 pm V −1 ), perhaps due to strong aggregation, the results demonstrate exceptional experimental Hyper Raleigh Scattering (HRS) β values. Eb2, for example has an HRS β value of 1650 ± 150 × 10 −30 esu at 900 nm in acetonitrile, which corresponds to μβ of 86 000 × 10 −48 esu and a μβ / M w figure of merit (FOM) of 121 × 10 −48 esu, where μ is the calculated dipole moment and M w is the chromophore's molecular weight. The chromophores are moderately stable in ambient conditions, their size and shape are easily modifiable, and they exhibit strong negative solvatochromism with solvent polarity.