Chemistry Reference
In-Depth Information
[n]Cycloparaphenylenes
1.6 nm
1.1 nm
0.98 nm
[12]CPP
em
= 450 nm
[8]CPP
em
= 545 nm
[7]CPP
em
= 592 nm
Semiconductor Quantum Dots
Linear
p
-Phenylenes
4
2 nm
em
= 450 nm
3 nm
em
= 525 nm
5 nm
em
= 620 nm
terphenyl
em
= 340 nm
sexiphenyl
em
= 390 nm
Red-Shifting Fluorescence
Fig. 23 Fluorescence trends in quantum dots, CPPs and OPPs [
43
]
With the elusive hydrocarbons finally in hand, Jasti obtained optical data for these
highly fluorescent aromatics and observed a similar absorbance for all diameters
(338-339 nm) and a fluorescence red shift with decreasing diameter. The largest
absorbance-emission shift, [9]CPP, is approximately 160 nm [
32
]. Oligopara-
phenylenes (OPPs), the linear analogues of CPPs, show a blue fluorescence shift
with decreasing length, following a “particle in a box” optoelectronic model [
62
].
Quantum dots also exhibit blue shifted fluorescence with decreasing size. The odd
trend for carbon nanohoops was attributed to the increased sp
3
character of the
smaller CPPs allowing for greater relaxation in the excited state, as well as the
diminished conjugation effects when considering these cyclic, infinitely conjugated
molecules. As will be seen, the fluorescence of all CPPs behaves in the same way
and has been a current topic of interest (Fig.
23
)[
38
,
48
,
57
,
58
].
4.3 Subsequent Syntheses: A New Field Emerges
In the years following the landmark synthesis by Jasti and Bertozzi, both the Itami
group at Nagoya University and Yamago and coworkers at Kyoto University
developed new synthetic routes to the cycloparaphenylenes.
In 2009, Itami et al. reported the selective synthesis of [12]CPP using methods
inspired by V¨gtle [
35
]. To do so, Itami synthesized bisboronate 50 and MOM-
protected 49. This protecting group simplifies purification. Reaction of a tenfold
