Chemistry Reference
In-Depth Information
Fig. 4 [Ru(bpy)
3
]
2+
and its photoexcited and redox forms that can be obtained by light and
electrochemical inputs [
32
,
33
]
These results show that [Ru(bpy)
3
]
2
þ
is able to process, and even interchange,
photonic and electronic inputs (Fig.
4
). The absorption spectra of the [Ru(bpy)
3
]
3
þ
,
[Ru(bpy)
3
]
2
þ
and [Ru(bpy)
3
]
þ
species are substantially different and it is not
difficult to choose appropriate absorbance thresholds related to the three
interconverting species at three different wavelengths (310, 450, and 530 nm).
Furthermore, [Ru(bpy)
3
]
2
þ
exhibits a luminescence band (
l
max
620 nm), whereas
[Ru(bpy)
3
]
3
þ
and [Ru(bpy)
3
]
þ
are not luminescent. By elaborating these spectro-
scopic properties and the photochemical and electrochemical processes, it has been
found that [Ru(bpy)
3
]
2
þ
can indeed perform as both an encoder and a decoder
(Fig.
5
)[
31
].
The example described above is only one of the many systems developed with
the aim of mimicking Boolean logic function at the molecular level [
28
]. Leaving
aside futuristic applications related to the construction of a chemical computer,
recent work shows that molecular logic devices could lead to practical applications
in a not-too-distant future. An example is the use of molecular logic gates for
tagging and identification of small objects in a large population [
34
], a method
termed molecular computational identification (MCID) [
35
]. Populations of micro-
scopic objects that need encoding are, e.g
.
, cells in diagnostics or polymer beads in
combinatorial chemistry. In this approach, a tag is represented by the unique
signature from a set of logic gates that is obtained in response to a defined set of
inputs under given experimental conditions.
To test the MCID method, single-input molecular logic gates 1-3 (Fig.
6
) were
linked to Tentagel-
S
-NH
2
polymer beads (100
m) by peptide coupling [
35
].
Compounds 1, 2, and 3 give a fluorescent output with PASS 1, YES, and NOT
logic, respectively, under the action of a proton input in solution, whereas
underivatized beads implement PASS 0 logic. Figure
6b
shows that beads tagged
m
