Control of Second-Order Nonlinear Optical Susceptibility in Ionically Self-Assembled Films by pH and Ionic Strength

ABSTRACTIonically self-assembled monolayers have been recently shown to spontaneously produce the noncentrosymmetric ordering that is required for a second order nonlinear optical (NLO) response. The precise thickness of each monolayer is determined by variables such as the pH and ionic strength of the immersion solutions. We show here that the relationship between polymer conformation and layer thickness dramatically affects the magnitude of the NLO response. The largest χ(2) values are found in the thinnest films, indicating that the NLO response is determined primarily by chromophores located at the layer interfaces, as opposed to those within the bulk of a layer.

Download Full-text

Second-order nonlinear optical thin films fabricated from ionically self-assembled monolayers

Technical Digest. Summaries of Papers Presented at the International Quantum Electronics Conference. Conference Edition. 1998 Technical Digest Series, Vol.7 (IEEE Cat. No.98CH36236) ◽

10.1109/iqec.1998.680091 ◽

2002 ◽

Cited By ~ 1

Author(s):

J.R. Heflin ◽

C. Figura ◽

D. Marciu ◽

Y. Liu ◽

Y.X. Wang ◽

...

Keyword(s):

Thin Films ◽

Nonlinear Optical ◽

Second Order ◽

Self Assembled Monolayers ◽

Assembled Monolayers ◽

Self Assembled

Download Full-text

Vibrational sum-frequency generation study of molecular structure, sterical constraints and nonlinear optical switching contrast of mixed alkyl-azobenzene self-assembled monolayers

Zeitschrift für Physikalische Chemie ◽

10.1515/zpch-2020-1655 ◽

2020 ◽

Vol 234 (7-9) ◽

pp. 1427-1452 ◽

Cited By ~ 1

Author(s):

Saira Riaz ◽

Gernot Friedrichs

Keyword(s):

Molecular Structure ◽

Nonlinear Optical ◽

Sum Frequency Generation ◽

Self Assembled Monolayers ◽

Sum Frequency ◽

Nlo Response ◽

Assembled Monolayers ◽

Self Assembled ◽

Frequency Generation ◽

Insight Into

AbstractSelf-assembled monolayers (SAMs) of azobenzene (AB) functionalized alkyl thiols on gold diluted with simple alkyl thiols provide a straightforward way to photochromic surfaces with high and tunable photoswitching efficiency. Trans-cis isomerization of the AB molecule changes the physical properties of the surface, including the nonlinear optical (NLO) response. Vibrational sum-frequency generation (VSFG) spectroscopy as a nonlinear type of laser spectroscopy offers surface- and orientation-sensitive insight into the molecular structure of mixed SAMs. In this study, VSFG as well as ultraviolet-visible (UV/Vis) spectroscopy has been employed to investigate the morphology, molecular structure, and NLO response of mixed SAMs with systematically varied surface composition. Methylazobenzene (MeAB) has been used as the molecular switch with the methyl substituent serving as orientational VSFG marker. Both short-chain and long-chain alkyl thiol co-ligands have been used to gain insight into the interplay between SAM structure and sterical constraints that are known to limit the free switching volume. Underlining the dominating role of sterical effects for controlling photochromic properties, a strong inhibition of the photoswitching efficiency and NLO response has been observed for the SAMs with an alkyl thiol co-ligand long enough to spatially extend into the layer of the MeAB chromophore. Overall, with <12% signal change, the relative NLO switching contrasts remained low in all cases. VSFG spectral trends clearly revealed that the presumably higher photoswitching efficiency upon dilution with the co-ligand is counteracted by a loss of structural order of the chromophore.

Download Full-text

Enhanced Second Order Nonlinear Optical Susceptibilities in Ionically Self-Assembled Films Incorporating Dianionic Molecules

MRS Proceedings ◽

10.1557/proc-660-jj8.30 ◽

2000 ◽

Vol 660 ◽

Author(s):

P.J. Neyman ◽

M.T. Guzy ◽

S. Shah ◽

K.E. Van Cott ◽

R.M. Davis ◽

...

Keyword(s):

Ionic Strength ◽

Nonlinear Optical ◽

Second Order ◽

Self Assembled Monolayer ◽

Polymer Layers ◽

Charged Polymers ◽

Nlo Response ◽

Polar Orientation ◽

Self Assembled ◽

Oppositely Charged

ABSTRACTIonically self-assembled monolayer (ISAM) films have been recently shown to spontaneously produce noncentrosymmetric ordering that gives rise to a substantial second order nonlinear optical (NLO) response. Typically, the ISAM films for NLO response are an assemblage of bilayers of oppositely charged polymers whose thickness can be controlled through variation of pH and ionic strength of the immersion solutions. Here, we study the effects of replacing the NLO-active polymer layers with layers of dianionic molecules. Films fabricated exclusively using polyelectrolytes contain some fraction of both randomly oriented and anti-parallel oriented chromophores. The incorporation of dianionic molecules within the ISAM films affords greater χ(2) due to increased net polar orientation of the chromophores.

Download Full-text