The resulting double bonds (C = C) are
chromophoric (increase the UVC reactivity of the reaction product) and are responsible for the yellow-red coloring of the exposed polymer.
In the case of photooxidation of nylons, the reaction will depend on the wavelength of light being absorbed, which in turn will depend on the presence of
chromophoric species.
By hybridizing a synthetic DNA template with a series of photoactive groups, the scientists formed three dimensional, light-activated
chromophoric memory units which may, for example, provide the ability to increase optical memory capacity.
The first was the oxidation of lignin which led to formation of paraquinone chromophoric structures within the first 250 hr of UV exposure, and the second was the reduction of the paraquinone structures to hydroquinones which led to photobleaching after 250 hr of UV exposure.
2] that the tensile properties and light stability of WPVC samples decreased with increasing wood flour content as a result of chromophoric groups in the wood flour that could accelerate the degradation of the PVC.
Recently, BP
chromophoric groups were found to easily produce radicals under both UVA (365 nm) light and even fluorescent light irradiation (21-23).
In particular, benzophenone chromophoric group, known to undergo light-excitation to n, [pi]* triplet states, are commonly used as photosensitizers in photochemistry.
H] NMR analyses for polystyrene and the resultant polymer were performed to investigate the degree of graft of benzophenone chromophoric group in the resultant polymer, as shown in Fig.
Thermal degradation of the cellulose fibres leads to a yellowing of the composite due to the production of
chromophoric groups.
The remaining part of the light penetrates into the object and is either absorbed by the molecular
chromophoric groups or reflected back towards the surface.
In general, the
chromophoric aromatic imide rings of conventional aromatic polyimides cause them to absorb at wavelengths less than 470 nm.
1]; the benzoyl moiety, which absorbs in the UV and the UV-visible part of the spectrum, can be considered as the
chromophoric group of most photoinitiators.
