Ask A Scientist© Chemistry Archive

 
 >>    name         Rhonda
 >>    status       educator
 >>    age          30s

 >>    Question -   What is it about certain plants that produce a dye?
 >> Please answer in a chemistry format.
 >
 >

Hi Rhonda...
Since antiquity dyes were used by man and until  19th century mostly
derived from plant sources. A large variety of plants were used as for
example:
Yellow: fruit of Ramnus species
Brown: acacia wood
Red:  dried flower head of safflower
Black: wood of diverse trees
With few exceptions natural dyes could only be used with the
aid  of an auxiliary inorganic chemical (called mordant) that
precipitated the colouring matter in order to be used.
When the synthetic dyes became to be made, theories
were developed in order to explain the relationship
between colour and structure.
The "chromophore" theory assumed the existence of
associated groups that intensified colours.
Later chromophores were generally identified connected
with quinones (oxidized structures derived from benzene ring).
These theories at large still are mantained today, but
nowadays it is recognized that the function of a chromophore
is to produce a strong absortion of radiation in the ultraviolet
or in the visible region of the spectrum.
The development of the quantum theory in the 20th century
heped also in the understanding of the interaction between
light and organic molecules: the absorption of visible radiation
by a dye raises the electronic energy of the molecule to
what is called  "excited state". That energy must be dissipated
as heat, phosphorescence or fluorescence, or in a chemical
reaction with the surroundings.

Ok?
Thanks for asking NEWTON!
Mabel
(Dr. Mabel Rodrigues)
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