In this paper, resonance Raman spectroscopy with dual-wavelength laser exci
tation is applied to study the chromatic phase properties of self-assembled
diacetylene monolayers on atomically flat Au surfaces. Laser excitation at
632.8 nm is utilized to exclusively monitor the longer conjugation length
blue-phase polydiacetylene (PDA) backbone structure, while laser excitation
at 514.5 nm is applied to probe the shorter conjugation length red phase.
This experimental design allows in situ measurement of the photophysics and
chemistry of the polymerization process within a single molecular layer. T
hese studies demonstrate the presence of multiple chromatic species of PDAs
within the same monolayer structure. Similar to observations for analogous
thin film and multilayer assemblies, systematic conversion from the higher
conjugation length blue form of the polymer to the shorter conjugation len
gth red form is observed upon extended UV irradiation. Moreover, a very lar
ge Raman dispersion of 130 cm(-1)/eV is measured, demonstrating the highly
conjugated nature of these monolayer polymers. Finally, backbone planarity
and strain during the polymerization process are assessed by using the corr
elation of double- and triple-bond stretching frequencies.