Abstract:
Chloride, bromide, pyridinium and quinolinium homologues of 4-(N-
hexadecylpyridinium-4-ylmethylidene-amino)-2,6-dichlorophenolate have been
investigated in solution, Langmuir and Langmuir-Blodgett films. Techniques including
spectroscopy, surface potential measurement, quartz crystal microbalance, surface
plasmon resonance, atomic force microscopy, reectometry and X-ray diffraction have
been used to characterise these molecular
systems.
In
solution,
solvatochroism was observed and Benisi-Hildebrand analysis revealed
dimeric
aggregation. Langmuir monolayers were compressed at the air/water interface
and
chromophore rotation was observed by surface potential measurement. Langmuir-
Blodgett monolayers showed lm-thickness dependence on the deposition-pressure.
Monolayer thicknesses between 6-24Ä were measured using SPR and molecular areas
between 40-l25Ä2 were measured
using a quartz crystal microbalance. Both the
molecular/s/area)and monolayer thicknesses were deposition-pressure dependent. The high
tilt
phases were visually distinguishable from the low tilt phases using atomic force
microscopy, The compounds showed phase behaviour that was predominantly alike for
the bromide and chloride
homologues but different for the pyridinium and quinolinum
homologues.
Multilayer Y-type films of the merocyanine dyes were analysed using reectometry and
deposition-pressure dependent thicknesses were found. Alternate layer structures of
NLO-active
hemicyanine amphiphiles were used to achieve homogeneous. orientation
ordering using active and inactive spacer layers. Ordering was achieved but the optical
efficiency was reduced by high proportions of inactive material and interlayer dipole
formation. Double chained
hemicyanine molecules were used to form Z-type structures
and
subsequent layers were found to significantly interdigitate. Different chain lengths
were found to
interdigitate by the length of the shortest chain.
Gas detection
experiments were undertaken on the quinolinium, dichloro merocyanine
using three optical geometries. The absorption method showed slow switching and poor
sensitivity. The Kretschmann SPR geometry showed high sensitivity and rapid switching.
The
grating SPR geometry showed rapid switching but was less sensitive than the ATR
method. Protonation of the
monolayers was investigated using hydrochloric acid gas,
acetic acid
vapour and stearic acid immobilised within the lm.