TY - JOUR

T1 - Quadratic and cubic nonlinear optical properties of salts of diquat-based chromophores with diphenylamino substituents

AU - Coe, Benjamin J.

AU - Fielden, John

AU - Foxon, Simon P.

AU - Helliwell, Madeleine

AU - Brunschwig, Bruce S.

AU - Asselberghs, Inge

AU - Clays, Koen

AU - Olesiak, Joanna

AU - Matczyszyn, Katarzyna

AU - Samoc, Marek

PY - 2010

Y1 - 2010

N2 - 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.

AB - 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.

U2 - 10.1021/jp106473e

DO - 10.1021/jp106473e

M3 - Journal article

VL - 114

SP - 12028

EP - 12041

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

SN - 1089-5639

IS - 45

ER -