6 research outputs found
Molecular Engineering of Polyphosphazenes and SWNT Hybrids with Potential Applications as Electronic Materials
Polymer/single-walled
carbon nanotube (SWNT) hybrids are promising candidates in applications
such as flexible and stretchable electronics. In this contribution,
we have examined structure–property relationships for constructing
new polyphosphazene–SWNT hybrids. UV–vis and Raman spectroscopy
studies revealed that the unique Pî—»N backbone enables strong
intermolecular donor–acceptor interactions between the polymer
and SNWTs. Furthermore, the polymeric backbone and the environment
at the P-centers collectively play important roles in the formation
of the hybrids. For polymers with shorter alkoxy substituents, the
donor–acceptor interactions between the PN backbone
and SWNTs play a crucial role in stabilizing the hybrid complexes,
but for polymers with longer alkoxy substituents, the CH−π
interactions and steric hindrance between the alkyl side chains and
SWNTs counterbalance each other and control the stability of the hybrid
complexes. Furthermore, the presence of fluorine and oxygen atoms
is detrimental to the stability of the hybrid complexes. New cross-linkable
polyphosphazenes with anthracene side units were also synthesized.
When photo-cross-linked, these polyphosphazene/SWNT hybrids showed
elastomeric characteristics and electronic properties that are promising
for future applications
Monumental Polovtsian Statues in Eastern Europe. The Archaeology, Conservation and Protection
Stone statues, indigenous to the early Turks, appeared in the vast territory of the Asian steppes, from Southern Siberia to Central Asia and across the foothills of the Ural Mountains. The custom originated among Cumans in Eastern Europe. The skill of erecting anthropomorphic stelae required proficiency in processing different kinds of stone and wood, and was characterized by artistic value of representations, as well as by the timeless aesthetics of the canon. The author presents the results of her formative studies into the collection of the Cuman sculptures of the Veliko-Anadol Forest Museum, Ukraine. The book delves into the history of research on Cuman stone stelae, resulting in great reading for all archeologists and historians alike
Nonlinear Absorbing Cationic Bipyridyl Iridium(III) Complexes Bearing Cyclometalating Ligands with Different Degrees of π‑Conjugation: Synthesis, Photophysics, and Reverse Saturable Absorption
We
report the synthesis, photophysics, and reverse saturable absorption
together with time-dependent density functional theory modeling of
seven cationic iridiumÂ(III) complexes bearing one 2,2′-bipyridine
ligand and two cyclometalating ligands (C^N ligand) with varied degrees
of Ï€-conjugation (HC^N = benzoÂ[H]Âquinoline in <b>1</b>, 1-phenylisoquinoline in <b>2</b>, 1-(2-pyridyl)Ânaphthalene
in <b>3</b>, 2-(2-pyridyl)Ânaphthalene in <b>4</b>, 1-(2-pyridyl)Âpyrene
in <b>5</b>, 1,2-diphenyl-pyrenoÂ[4,5-<i>d</i>]Âimidazole
in <b>6</b>, and 3-(2-pyridyl)Âperylene in <b>7</b>). All
complexes possess ligand-localized <sup>1</sup>Ï€,Ï€* transitions
as the major absorption bands and lower-energy <sup>1</sup>MLCT (metal-to-ligand
charge transfer)/<sup>1</sup>LLCT (ligand-to-ligand charge transfer)
transitions in their ultraviolet–visible absorption spectra.
The extended π-conjugation in the cyclometalating ligands of
complexes <b>5</b>–<b>7</b> causes a significant
red-shift of the major absorption bands with increased molar extinction
coefficients with respect to those of complexes <b>1</b>–<b>4</b> that contain less conjugated C^N ligands. All complexes
are emissive in solutions at room temperature and in glassy matrix
at 77 K. The emitting states are assigned to <sup>3</sup>Ï€,Ï€*
(C^N ligand localized) /<sup>3</sup>MLCT for <b>1</b>, <sup>3</sup>Ï€,Ï€*/<sup>3</sup>MLCT/<sup>3</sup>LMCT (ligand-to-metal
charge transfer) for <b>2</b>–<b>4</b>, pure <sup>3</sup>π,π* transitions for <b>5</b> and <b>6</b>, and <sup>3</sup>π,π*/<sup>3</sup>MLCT/<sup>3</sup>LMCT/<sup>3</sup>LLCT for <b>7</b>. Complex <b>5</b> possesses the lowest emission energy because the larger conjugation
and the most delocalized character of the <sup>3</sup>Ï€,Ï€*
transition within the C^N ligand in this complex. Complexes <b>1</b>, <b>4</b>, and <b>7</b> possess larger contribution
of charge transfer characters in their lowest triplet excited states.
Therefore, the transient absorption of these three complexes is broad
but short-lived (90–300 ns). In contrast, complexes <b>2</b>, <b>3</b>, <b>5</b>, and <b>6</b> all give long-lived
(2.0–19.5 μs) triplet transient absorption in the visible
spectral region of ca. 450–700 nm, which can be regarded as
emanating predominantly from the C^N ligand-centered <sup>3</sup>Ï€,Ï€*
state. The reverse saturable absorption (RSA) of these complexes was
evaluated at 532 nm for nanosecond laser pulses. The results demonstrate
that these complexes, except for <b>7</b>, all exhibit strong
RSA for nanosecond laser pulses at 532 nm, with a trend of <b>7</b> < <b>1</b> < <b>4</b> < <b>6</b> < <b>5</b> ≈ <b>2</b> ≈ <b>3</b>
Effects of Extended π‑Conjugation in Phenanthroline (N<sup>∧</sup>N) and Phenylpyridine (C<sup>∧</sup>N) Ligands on the Photophysics and Reverse Saturable Absorption of Cationic Heteroleptic Iridium(III) Complexes
Five
new iridiumÂ(III) complexes (3,8-R-Phen)ÂIrÂ(2-(3-R′-phenyl)Âpyridine)<sub>2</sub> (<b>1</b>, R = fluoren-2-yl, R′ = H; <b>2</b>, R = 7-benzothiazolylfluoren-2-yl, R′ = H; <b>3</b>, R = H, R′ = fluoren-2-yl; <b>4</b>, R = H, R′
= 7-benzothiazolylfluoren-2-yl; <b>5</b>, R = R′ = 7-benzothiazolylfluoren-2-yl)
with fluoren-2-yl or 7-benzothiazolylfluoren-2-yl substituent on the
2-phenylpyridine (C<sup>∧</sup>N) and/or phenanthroline (N<sup>∧</sup>N) ligands were synthesized and characterized. Their
photophysical properties were investigated systematically via UV–vis
absorption, emission, and transient difference absorption spectroscopy.
Time-dependent density functional theory (TDDFT) calculations were
performed to complement the experimental data and aid in our understanding
of the characters of optical transitions. In addition, reverse saturable
absorption was demonstrated at 532 nm for all complexes using nanosecond
laser pulses. All complexes possess a weak low-energy tail that is
attributed to <sup>1,3</sup>MLCT (metal-to-ligand charge transfer)/<sup>1,3</sup>LLCT (ligand-to-ligand charge transfer) transitions. The
major absorption bands below 475 nm for <b>1</b>–<b>5</b> arise from the <sup>1</sup>π,π* and intraligand
(<sup>1</sup>ILCT) transitions within the N<sup>∧</sup>N or
C<sup>∧</sup>N ligands. Attachment of fluoren-2-yl or 7-benzothiazolylfluoren-2-yl
substituents on N<sup>∧</sup>N ligand results in stronger red-shifts
of the main absorption band to 400 and 408 nm for <b>1</b> and <b>2</b>, respectively, as compared to 321 and 361 nm in complexes <b>3</b> and <b>4</b> with the same substituents on the C<sup>∧</sup>N
ligands. In contrast, the <sup>1,3</sup>MLCT/<sup>1,3</sup>LLCT transitions
in <b>1</b> and <b>2</b> are just slightly red-shifted
as compared to those in <b>3</b> and <b>4</b>. The emission
of complexes <b>1</b> and <b>2</b> is attributed to the
N<sup>∧</sup>N ligand-centered <sup>3</sup>π,π*
state with some admixture of <sup>3</sup>MLCT/<sup>3</sup>ILCT/<sup>3</sup>LLCT characters for <b>1</b>. In contrast, the emission
of <b>3</b> and <b>4</b> emanates exclusively from the <sup>3</sup>MLCT/<sup>3</sup>LLCT states. For complex <b>5</b>,
which contains 7-benzothiazolylfluoren-2-yl substituents on both the
C<sup>∧</sup>N and the N<sup>∧</sup>N ligands, the emission
predominantly arises from the <sup>3</sup>MLCT/<sup>3</sup>LLCT states
with a small portion of N<sup>∧</sup>N ligand-localized <sup>3</sup>π,π* character. All complexes exhibit broadband
triplet excited-state absorption in the visible to the near-IR region,
with the major absorption bands bathochromically shifted in <b>1</b> and <b>2</b> as compared to those in <b>3</b> and <b>4</b>. The stronger excited-state absorption leads
to dramatic reverse saturable absorption (RSA) at 532 nm for nanosecond
laser pulses. The RSA strength decreases as <b>5</b> ≈ <b>2</b> > <b>4</b> ≈ <b>1</b> > <b>3</b>, which is primarily determined by the ratio of the triplet excited-state
absorption cross section relative to that of the ground state. Extended
π-conjugation in the N<sup>∧</sup>N ligand obviously
increases the RSA of complexes <b>1</b>, <b>2</b>, and <b>5</b> in comparison to those with π-conjugated substituents
only on the C<sup>∧</sup>N ligands (<b>3</b> and <b>4</b>)
Synthesis and Characterization of Heterobimetallic Iridium–Aluminum and Rhodium–Aluminum Complexes
We
demonstrate the synthesis and characterization of a new class of late-transition-metal–aluminum
heterobimetallic complexes via a novel synthetic pathway. Complexes
of this type are exceedingly rare. Joint experimental and theoretical
data sheds light on the electronic effect of ligands containing aluminum
moieties on late-transition-metal complexes
Influence of Different Diimine (N<sup>∧</sup>N) Ligands on the Photophysics and Reverse Saturable Absorption of Heteroleptic Cationic Iridium(III) Complexes Bearing Cyclometalating 2‑{3-[7-(Benzothiazol-2-yl)fluoren-2-yl]phenyl}pyridine (C<sup>∧</sup>N) Ligands
Four heteroleptic cationic iridiumÂ(III)
complexes containing cyclometalating
2-{3-[7-(benzothiazol-2-yl)Âfluoren-2-yl]Âphenyl}Âpyridine ligand and
different diimine (N<sup>∧</sup>N) ligands (N<sup>∧</sup><i>N</i> = 2-(pyridin-2-yl)Âquinoline (<b>1</b>),
1,10-phenanthroline (<b>2</b>), 2,2′-biquinoline (<b>3</b>), and 1,1′-biisoquinoline (<b>4</b>)) and a
reference complex bearing 2-(pyridin-2-yl)Âquinoline and 2-phenylpyridine
ligands (<b>5</b>) were synthesized and characterized. The influence
of the diimine (N<sup>∧</sup>N) ligand on the photophysics
of these complexes has been systematically investigated via spectroscopic
methods and by time-dependent density functional theory (TDDFT). All
complexes exhibit N<sup>∧</sup>N or C<sup>∧</sup>N ligand
localized <sup>1</sup><i>Ï€,Ï€</i>* transitions
below 400 nm, and broad and structureless metal-to-ligand and ligand-to-ligand
charge transfer (<sup>1</sup>MLCT/<sup>1</sup>LLCT) absorption bands
between 400 and 450 nm, and weak <sup>3</sup>MLCT/<sup>3</sup>LLCT
absorption above 450 nm. Increasing the π-conjugation of the
N<sup>∧</sup>N ligand causes enhanced molar extinction coefficients
of the absorption bands and a bathochromic shift of the <sup>3</sup>MLCT/<sup>3</sup>LLCT band. All complexes show orange to red phosphorescence
at room temperature, with the emitting state being predominantly assigned
to <sup>3</sup>MLCT/<sup>3</sup>LLCT states for <b>1</b>–<b>5</b>, but with some <sup>3</sup><i>π,π</i>* contributions for <b>3</b> and <b>5</b>. Extending
the π-conjugation of the N<sup>∧</sup>N ligand induces
a pronounced red-shift of the emission band and decreases the emission
lifetime and quantum yield. Complexes <b>1</b>–<b>5</b> exhibit relatively strong singlet and triplet transient
absorption from 450 to 800 nm, where the reverse saturable absorption
(RSA) could occur. Nonlinear transmission experiments at 532 nm using
nanosecond laser pulses demonstrate that complexes <b>1</b>–<b>5</b> are strong reverse saturable absorbers at 532 nm