Chemistry Reference
In-Depth Information
shared the 1981 Nobel Prize in Chemistry. Such a poem, which describes the
“divine” growing of a vine around a tall tree, begins with the following lines:
“Alive? The /vines just push/the question/aside, a/green muff for/these trees, coat-/
ing them real/tight like a crosslinked po-/lymer gone/mad. The prob-/lem in spring/
is the trees'-/are they? And /will they be?” This poem is another marvelous
description of the power of photosynthesis.
5 Clever Molecules
Although the most creative act in chemistry is frequently considered to be “the
design and creation of new molecules” [
16
], creativity in chemistry in the last few
years has more often arisen from novel conceptual interpretations of well-known
chemical reactions of established molecules [
17
-
21
]. In many fields of art and
science, creativity results indeed from reconsidering old materials with a new
design in mind. A typical example of exploiting well-known properties of old
molecules for new achievements concerns the field of information processing.
In 1993 the analogy between molecular switches and logic gates was experi-
mentally demonstrated [
22
]. Since then, processing photonic, electronic, and
chemionic signals by molecules in solution has been proposed [
17
-
20
,
23
-
28
]as
an alternative route to solid-state molecular electronics towards the design and
construction of the much-sought chemical computer [
29
,
30
]. The field has recently
developed from simple switches to produce more complex molecular systems that
are capable of performing a variety of classical logic functions [
23
-
28
].
A particularly interested case of “clever” molecule is the very simple and well-
known metal complex, [Ru(bpy)
3
]
2+
(bpy
2,2
0
-bipyridine), which was found to
perform as both an encoder and a decoder of a combination of electronic and
photonic inputs and outputs [
31
].
The chemical, photochemical, and electrochemical behavior of [Ru(bpy)
3
]
2
þ
and of hundreds of its derivatives has been extensively investigated in the past
30 years [
32
,
33
]. The ground state complex (Fig.
4
) can be excited by visible light
with formation of a spin-allowed excited state, **[Ru(bpy)
3
]
2
þ
, which undergoes
fast and efficient radiationless deactivation to form the spin-forbidden, long-lived,
and luminescent *[Ru(bpy)
3
]
2
þ
excited state. [Ru(bpy)
3
]
2
þ
can also undergo
reversible one-electron oxidation and reduction processes (e.g., in acetonitrile
solution), which become energetically much more favorable starting from *[Ru
(bpy)
3
]
2
þ
because of the extra energy available to the excited state (photoinduced
electron transfer, Fig.
4
). It is also well known that the comproportionation reaction
between the oxidized [Ru(bpy)
3
]
3
þ
and the reduced [Ru(bpy)
3
]
þ
species (
1
)is
strongly exergonic and can in fact generate a ground [Ru(bpy)
3
]
2
þ
and an excited
*[Ru(bpy)
3
]
2
þ
species, followed by radiative deactivation of the latter (lumines-
cence induced by electron transfer):
¼
3
þ
Þ
3
þ
!½
2
þ
2
þ
½
Ru
ð
bpy
Þ
3
þ½
Ru
ð
bpy
Ru
ð
bpy
Þ
3
þ½
Ru
ð
bpy
Þ
3
(1)
