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 P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 iridium­(III) complexes bearing one 2,2′-bipyridine ligand and two cyclometalating ligands (C^N ligand) with varied degrees of π-conjugation (HC^N = benzo­[H]­quinoline in <b>1</b>, 1-phenylisoquinoline in <b>2</b>, 1-(2-pyridyl)­naphthalene in <b>3</b>, 2-(2-pyridyl)­naphthalene in <b>4</b>, 1-(2-pyridyl)­pyrene in <b>5</b>, 1,2-diphenyl-pyreno­[4,5-<i>d</i>]­imidazole in <b>6</b>, and 3-(2-pyridyl)­perylene in <b>7</b>). All complexes possess ligand-localized ¹π,π* transitions as the major absorption bands and lower-energy ¹MLCT (metal-to-ligand charge transfer)/¹LLCT (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 ³π,π* (C^N ligand localized) /³MLCT for <b>1</b>, ³π,π*/³MLCT/³LMCT (ligand-to-metal charge transfer) for <b>2</b>–<b>4</b>, pure ³π,π* transitions for <b>5</b> and <b>6</b>, and ³π,π*/³MLCT/³LMCT/³LLCT for <b>7</b>. Complex <b>5</b> possesses the lowest emission energy because the larger conjugation and the most delocalized character of the ³π,π* 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 ³π,π* 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^∧N) and Phenylpyridine (C^∧N) Ligands on the Photophysics and Reverse Saturable Absorption of Cationic Heteroleptic Iridium(III) Complexes

Five new iridium­(III) complexes (3,8-R-Phen)­Ir­(2-(3-R′-phenyl)­pyridine)₂ (<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^∧N) and/or phenanthroline (N^∧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 ^1,3MLCT (metal-to-ligand charge transfer)/^1,3LLCT (ligand-to-ligand charge transfer) transitions. The major absorption bands below 475 nm for <b>1</b>–<b>5</b> arise from the ¹π,π* and intraligand (¹ILCT) transitions within the N^∧N or C^∧N ligands. Attachment of fluoren-2-yl or 7-benzothiazolylfluoren-2-yl substituents on N^∧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^∧N ligands. In contrast, the ^1,3MLCT/^1,3LLCT 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^∧N ligand-centered ³π,π* state with some admixture of ³MLCT/³ILCT/³LLCT characters for <b>1</b>. In contrast, the emission of <b>3</b> and <b>4</b> emanates exclusively from the ³MLCT/³LLCT states. For complex <b>5</b>, which contains 7-benzothiazolylfluoren-2-yl substituents on both the C^∧N and the N^∧N ligands, the emission predominantly arises from the ³MLCT/³LLCT states with a small portion of N^∧N ligand-localized ³π,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^∧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^∧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^∧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^∧N) Ligands

Four heteroleptic cationic iridium­(III) complexes containing cyclometalating 2-{3-[7-(benzothiazol-2-yl)­fluoren-2-yl]­phenyl}­pyridine ligand and different diimine (N^∧N) ligands (N^∧<i>N</i> = 2-(pyridin-2-yl)­quinoline (<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)­quinoline and 2-phenylpyridine ligands (<b>5</b>) were synthesized and characterized. The influence of the diimine (N^∧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^∧N or C^∧N ligand localized ¹<i>π,π</i>* transitions below 400 nm, and broad and structureless metal-to-ligand and ligand-to-ligand charge transfer (¹MLCT/¹LLCT) absorption bands between 400 and 450 nm, and weak ³MLCT/³LLCT absorption above 450 nm. Increasing the π-conjugation of the N^∧N ligand causes enhanced molar extinction coefficients of the absorption bands and a bathochromic shift of the ³MLCT/³LLCT band. All complexes show orange to red phosphorescence at room temperature, with the emitting state being predominantly assigned to ³MLCT/³LLCT states for <b>1</b>–<b>5</b>, but with some ³<i>π,π</i>* contributions for <b>3</b> and <b>5</b>. Extending the π-conjugation of the N^∧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