Linear and non-linear optical properties of the different Langmuir–Blodgett phases of C_nH_2n+1–Q3CNQ

Abstract

OQX(Z)-a-cyano-~-(N-hexadecylquinolin-4-ylium)-4-styryldicyanomethanide, C16H3,-Q3CNQ, has two Langmuir-Blodgett (LB) phases that differ in thickness, tilt angle and second-order susceptibility. For phase I, /=2.2 nm layer-', 4 = 8 " and ~( ~) = 1 8 0 pm V-' at 1.064 pm, whereas for phase II, /=1.6 nm layer-', #=24" and ~( ~) = 1 0 0 pm V-'. The susceptibility of phase I is the highest so far reported for an LB multilayer; the structure is non-centrosymmetric (Ztype) and, as predicted by theory, the second-harmonic intensity varies as /2w(N)=/2w(,)N2 as N increases from 1 to 200 layers. In contrast, C10H2,-Q3CNQ has a low susceptibility (x,z(~)= 6 pm V-') and neutron reflectivity studies have indicated an antiparallel alignment of chromophores at the air/water interface.

Counterion Effects on the Structure of Langmuir-Blodgett Films of a Benzothiazolium Dye

“…Based on the surface plasmon resonance (SPR) analysis of deposited films of the iodide salt there is evidence that, in this case, the molecule has a stretched motif. Although the existence of a hydrophobic chain juxtaposed to the interface is unusual, such alignments have previously been confirmed by neutron reflectivity studies on Langmuir films of Ζ-β-(N-decyl-4-quinolinium)-α-cyano4-styryldicyanomethanide (C10H21-Q3CNQ) which forms antiparallel dimers at the air-water interface [4].…”

“…SPR reflectivity data were first corrected for reflections at the entrance and exit faces of the prism and analysed by comparison to the Fresnel reflection formulae by a method previously described [4,20,21]. The thickness (typically ca.…”

“…Asymmetry can be induced by tailoring the materials to force X-type or Z-type deposition [1][2][3][4][5][6][7] or be acquired by interleaving V-type layers with optically inactive spacers [8][9][10][11][12]. For homomolecular films in excess of 100 layers such long range non-centrosymmetry has only been realised for a modicum of materials, namely 2-docosylamino5-nitropyridine (DCANP) [13], a quinolinium zwitterion (C16H33-Q3CNQ) [4] and a series of unconventional LB dyes comprising a chromophore with hydrophobic chains at opposing ends [5][6][7].…”

Understanding the optical spectroscopy of amphiphilic molecular rectifiers: A density functional approach

“…11,12 From the calculation results, the charge transfer is found to be confined to individual chromophores and no intermolecular orbital crossover can be detected. The calculated absorbance spectrum from the dimer supercell gives exactly the same absorption features as that from the single unit cell.…”

“…For example, the optical absorption features and optical nonlinearity (second harmonic generation, i.e., SHG). [10][11][12] of LB films of long chain Q3CNQ homologues have been found to be markedly different from those of the short chain homologues. A visible region absorption band is seen at 563 nm for long chain homologue LB films whereas the band lies at 614 nm for short chain homologues; SHG signals from the long chain homologue LB films are fairly large but are nearly absent for short chain Q3CNQ homologues.…”