Chemistry Reference
In-Depth Information
F
Bu
F
F
Bu
S
F
F
Bu
S
Bu
NH
N
Bu
Se
Se
S
Bu
Se
Se
N
HN
S
Bu
S
Bu
Bu
F
F
S
Bu
S
Bu
S
F
F
Bu
Bu
F
Bu
Bu
Bu
Macrocyclic thiophene 30-mers
34
π
octaphyrin
fIgure 11.31
Two of the highest two-photon absorption cross-section (~100,000 GM) organic materials [132, 133].
VIS-VIS
NIR-VIS
NIR-NIR
NIR excitation
NIR emission
Visible excitation NIR excitation
S
n
S
1
Intermediate
state
For imaging
Imaging organells
fIgure 11.32
Schematic representations of the mechanism of the two-photon induced emission (left) and advantages of NIr excita-
tion and NIr emission as
in vitro
/
in vivo
imaging agents.
to recently reported multi-photon materials in the period 2009 to 2011, with an emphasis on their two-photon absorption
cross-sections for
in vitro
imaging. One needs to notice that even though some of the molecular and dendrimeric two-photon
absorbers possess very high two-photon absorption cross-sections, their poor water solubility and cell permeability render
them unsuitable for
in vitro
applications. The current available cell permeable materials for two-photon bioimaging gener-
ally have their two-photon absorption cross-sections of >20 GM. Five organic molecules with impressive two-photon
absorption cross-section from 600 GM to 2500 GM are shown in Figure 11.33.
11.5.2
two-photon Induced Visible
In Vitro
organelle-specific Imaging
The study of cellular organelles and their associated signalling pathways in normal and malignant human cells lead to a
gradual understanding of how normal cells transform into malignant cells. There have been already a lot of organelle-specific
organic-based fluorescent staining agents in the market [144]. However, the majority of them are comprised of ordinary linear
fluorophores that can only be excited in the ultraviolet-visible region. Figure 11.34 depicts some examples of cell permeable,
two-photon excitable organic fluorescent probes that have been used in the imaging of biologically meaningful species in
various cancer and normal cell lines.
