Quadratic and cubic nonlinear optical properties of salts of diquat-based chromophores with diphenylamino substituents

Coe, Benjamin J., Fielden, John ORCID: https://orcid.org/0000-0001-5963-7792, Foxon, Simon P., Helliwell, Madeleine, Brunschwig, Bruce S., Asselberghs, Inge, Clays, Koen, Olesiak, Joanna, Matczyszyn, Katarzyna and Samoc, Marek (2010) Quadratic and cubic nonlinear optical properties of salts of diquat-based chromophores with diphenylamino substituents. The Journal of Physical Chemistry A, 114 (45). pp. 12028-12041. ISSN 1089-5639

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Abstract

A series of chromophoric salts has been prepared in which 4-(diphenylamino)phenyl (Dpap) electron donor groups are connected to electron-accepting diquaternized 2,2′-bipyridyl (diquat) units. The main aim is to combine large quadratic and cubic nonlinear optical (NLO) effects in potentially redox-switchable molecules with 2D structures. The chromophores have been characterized as their PF6− salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. The visible absorption spectra are dominated by intense π → π* intramolecular charge-transfer (ICT) bands, and all of the compounds show two reversible or quasireversible diquat-based reductions and partially reversible Dpap oxidations. Single crystal X-ray structures have been obtained for one salt and for the precursor compound (E)-4-(diphenylamino)cinnamaldehyde, both of which adopt centrosymmetric space groups. First hyperpolarizabilities β have been measured by using hyper-Rayleigh scattering (HRS) with a 800 nm laser, and Stark (electroabsorption) spectroscopy of the ICT bands affords estimated static first hyperpolarizabilities β0. The directly and indirectly derived β values are large and generally increased substantially for the bis-Dpap derivatives when compared with their monosubstituted analogues. Polarized HRS studies show that the NLO responses of the disubstituted species are dominated by “off-diagonal” βzyy components. Lengthening the diquaternizing alkyl unit lowers the electron-acceptor strength and therefore increases the ICT energies and decreases the E1/2 values for diquat reduction. However, compensating increases in the ICT intensity prevent significant decreases in the Stark-based β0 responses. Cubic NLO properties have been measured by using the Z-scan technique over a wavelength range of 520−1600 nm, revealing relatively high two-photon absorption cross-sections of up to 730 GM at 620 nm for one of the disubstituted chromophores.

Item Type:	Article
Faculty \ School:	Faculty of Science > School of Chemistry
UEA Research Groups:	Faculty of Science > Research Groups > Chemistry of Materials and Catalysis Faculty of Science > Research Groups > Chemistry of Light and Energy Faculty of Science > Research Groups > Energy Materials Laboratory
Depositing User:	Users 2731 not found.
Date Deposited:	17 Oct 2012 09:44
Last Modified:	09 Jan 2023 16:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/39947
DOI:	10.1021/jp106473e

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