Abstract:
Three novel donor-acceptor systems have been characterised through
their spectroscopic properties, magnetic susceptibility, conductivity
and second harmonic generation.
The magnetic properties of (H2DPE)xx+(DPE)^ x(TCNQ)gX and
(H2DPA)xx+(DPA) 1 x(TCNQ)gX' where DPE = 1,2-di(4-pyridyl)ethylene,
DPA = 1,2-di(4-pyridyl)ethane, TCNQ = tetracyanoquinodimethane and
H2 signifies proton diquaternisation, have been found to depend upon
the stoichiometry: For x > \ the magnetic susceptibility decreases
with increasing x whereas for x ~ \ it is anomolously large, being
ferromagnetically enhanced above the Curie Law value. A possible model
involving spin dilution is proposed and its predictions are compared
with the experimental results. Langmuir-Blodgett (LB) films of the
long-chained analogues of the materials, (C^g)2DPE (TCNQ) 2 and
(Cig^DPE^TCNQ)^" where (C16) 2 = bis(hexadecyl) were deposited and
characterised. The conductivities of the LB films of the mixed valence
system were found to be ~ 1000 times greater than those of the system
lacking TCNQ^ molecules.
Multiple layer LB films of trans-4-[4- (dimethylamino)styryl]-1-
octadecylpyridinium iodide and trans-4-[4-(dimethylamino)styryl]-1-
octadecylquinolinium iodide interleaved with 4,4'-dioctadecyl-3,5,3',5'
-tetramethyldipyrrylmethene hydrobromide were deposited. The materials
form an interlocking bilayer structure which renders their LB films
exceptionally well-organised. The films’ second harmonic generation
was investigated and one film was found to give the largest second
harmonic signal yet seen from an LB structure.
