Fluorescence imaging in the second near-infrared window
(NIR-II,
1000–1700 nm) using small-molecule dyes has high potential
for clinical use. However, many NIR-II dyes suffer from the emission
quenching effect and extremely low quantum yields (QYs) in the practical
usage forms. The AIE strategy has been successfully utilized to develop
NIR-II dyes with donor–acceptor (D–A) structures with
acceptable QYs in the aggregate state, but there is still large room
for QY improvement. Here, we rationally designed a NIR-II emissive
dye named TPE-BBT and its derivative (TPEO-BBT) by changing the electron-donating
triphenylamine unit to tetraphenylethylene (TPE). Their nanoparticles
exhibited ultrahigh relative QYs of 31.5% and 23.9% in water, respectively.
By using an integrating sphere, the absolute QY of TPE-BBT nanoparticles
was measured to be 1.8% in water. Its crystals showed an absolute
QY of 10.4%, which is the highest value among organic small molecules
reported so far. The optimized D–A interaction and the higher
rigidity of TPE-BBT in the aggregate state are believed to be the
two key factors for its ultrahigh QY. Finally, we utilized TPE-BBT
for NIR-II photoluminescence (PL) and chemiluminescence (CL) bioimaging
through successive CL resonance energy transfer and Förster
resonance energy transfer processes. The ultrahigh QY of TPE-BBT realized
an excellent PL imaging quality in mouse blood vessels and an excellent
CL imaging quality in the local arthrosis inflammation in mice with
a high signal-to-background ratio of 130. Thus, the design strategy
presented here brings new possibilities for the development of bright
NIR-II dyes and NIR-II bioimaging technologies.
X-ray emission from a comet was observed for the first time in 1996. One of the mechanisms believed to be contributing to this surprisingly strong emission is the interaction of highly charged solar wind ions with cometary gases. Reported herein are total absolute charge-exchange and normalized line-emission (X-ray) cross sections for collisions of high-charge state (+3 to +10) C, N, O, and Ne ions with the cometary species H2O and CO2. It is found that in several cases the double charge-exchange cross sections can be large, and in the case of C3+ they are equal to those for single charge exchange. Present results are compared to cross section values used in recent comet models. The importance of applying accurate cross sections, including double charge exchange, to obtain absolute line-emission intensities is emphasized.
The combination of chirality and semiconducting properties
has
enabled chiral metal-halide semiconductors (MHS) to be promising candidates
for spin- and polarization-resolved optoelectronic devices. Although
several chiral MHS with rich chemical and structural diversity have
been reported lately, the macroscopic origin of chiroptical activity
remains elusive. Here, combining spectroscopic measurements and Mueller
matrix analysis, we discover that the previously reported “apparent”
anisotropy factor measured from circular dichroism (CD) in chiral
MHS thin films is not an intrinsic chiroptical property, but rather,
arising from an interference between the film’s linear birefringence
(LB) and linear dichroism (LD). We verify the presence of LB and LD
effects in both one-dimensional and zero-dimensional chiral MHS thin
films. We establish spectroscopic methods to decouple the genuine
CD from other spurious contributions, which allows a quantitative
comparison of the intrinsic chiroptical activity across different
chiral MHS. The relationship between the structure and the genuine
chiroptical activity is then uncovered, which is well described by
the chirality-induced spin–orbit coupling in the chiral structures.
Our study unveils the macroscopic origin of chiroptical activity of
chiral MHS and provides design principles for obtaining high anisotropic
factors for future chiral optoelectronic applications.
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