Biomedical Engineering Reference
In-Depth Information
Aggregation
(a)
Infrared laser
O
O
O
O
N
N
Decoupling
O
O
O
O
N
N
O
O
O
N
N
O
Silk fibril
Hydrogen bond
(b)
(c)
4NF
@THF
4NF
@silk fiber
4NF
solid powder
1.0
0.8
0.6
0.4
0.2
0.0
500
600
700
200
μ
m
Wavelenght (nm)
Figure 7.6
(a) Proposed model for the
silk fibril decoupling effect by the molecu-
lar recognition of
4NF
and
8NF
molecules:
the ''silk fibril segments'' consist of sev-
eral
β
sheets connected by random coils or
α
helices forming a polypeptide chain net-
work. Two-photon fluorophores
4NF
/
8NF
was decoupled by their specific binding
with the amide groups in the silk fibroin
molecules, by means of hydrogen bonds.
(b) The one-photon fluorescence spectra of
4NF
in THF solution, in silk fibers and in
the solid powder form. (c) A two-photon flu-
orescence microscope image showing three-
dimensional view of
8NF
fabric scaffold in a
culture medium. (Reproduced with permis-
sion Copyright 2012, Wiley. Reprinted with
permission from Ref. [68].
©
2012 Wiley-VCH
Verlag GmbH & Co. KGaA, Weinheim.)
7.4.3.1
Two-Photon Absorption Cross-Section of Designed Organic Molecules
To further illustrate the molecular recognition approach in functionalization
of silk-related materials, we will outline below the synthesis of styryl-fluorene
molecules with the same terminal nitro groups and different aliphatic
chains, namely 2,7-bis[2-(4-nitrophenyl)ethenyl]-9,9-dibutylfluorene (
4NF
)and
2,7-bis[2-(4-nitrophenyl)ethenyl]-9,9-dioctylfluorene
(
8NF
).
For
comparison,
2,7-bis[2-(4-methylphenyl)ethenyl]-9,9-dioctylfluorene (
) with two methyl
terminal groups was also synthesized. Z-scan measurements showed that the TPA
cross-section of
8MF
8NF
is 1199 Goeppert-Mayer (GM), which is larger than that
of
(905 GM) in tetrahydrofuran (THF). In contrast, the TPA cross-section
of
8MF
, in which the electron-withdrawing nitro groups of
8NF
are replaced by
methyl groups, is as low as 514 GM.
4NF
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