Visible-Light Organic Photosensitizers Based on 2-(2-Aminophenyl)benzothiazoles for Photocycloaddition Reactions.

Synthesis and characterization of high triplet energy polyfluorene bearing m-tetraphenylsilane segment as a polymer host for green phosphorescent polymer light emitting diodes

Photophysical properties and photoinduced polymerisation activity of novel 1-chloro-4-oxy/acyloxythioxanthone initiators

A supramolecular dyad, BP-(amidinium-carboxylate)-NBD is constructed, in which benzophenone (BP) and norbornadiene (NBD) are connected via an amidinium-carboxylate salt bridge. The photophysical and photochemical properties of the assembled BP-(amidinium-carboxylate)-NBD dyad are examined. The phosphorescence of the BP chromophore is efficiently quenched by the NBD group in BP-(amidinium-carboxylate)-NBD via the salt bridge. Time-resolved spectroscopy measurements indicate that the lifetime of the BP triplet state in BP-(amidinium-carboxylate)-NBD is shortened due to the quenching by the NBD group. Selective excitation of the BP chromophore results in isomerization of the NBD group to quadricyclane (QC). All of these observations suggest that the triplet-triplet energy transfer occurs efficiently in the BP-(amidinium-carboxylate)-NBD salt bridge system. The triplet-triplet energy transfer process proceeds with efficiencies of approximately 0.87, 0.98 and the rate constants 1.8x10(3) s(-1), and 1.3x10(7) s(-1) at 77 K and room temperature, respectively. The mechanism for the triplet-triplet energy transfer is proposed to proceed via a "through-bond" electron exchange process, and the non-covalent bonds amidinium-carboxylate salt bridge can mediate the triplet-triplet energy transfer process effectively for photochemical conversion.

Carborane-based host materials were prepared to fabricate deep blue phosphorescence organic light-emitting diodes (PHOLEDs), which constituted three distinctive geometrical structures stemming from the corresponding three different isomeric forms of carboranes, namely, ortho-, meta-, and para-carboranes. These materials consist of two carbazolyl phenyl (CzPh) groups as photoactive units on each side of the carborane carbons to be bis[4-(N-carbazolyl)phenyl]carboranes, o-Cb, m-Cb, and p-Cb. To elaborate on the role of the carboranes, comparative analogous benzene series (o-Bz, m-Bz, and p-Bz) were prepared, and their photophysical properties were compared to show that advantageous photophysical properties were originated from the carborane structures: high triplet energy. Unlike m-Bz and p-Bz, carborane-based m-Cb and p-Cb showed an unconjugated nature between two CzPh units, which is essential for the blue phosphorescent materials. Also, the carborane hosts showed high glass transition temperatures (T(g)) of 132 and 164 °C for m-Cb and p-Cb, respectively. Albeit p-Cb exhibited slightly lower hole mobility when compared to p-Bz, it still lies at the high end hole mobility with a value of 1.1 × 10(-3) cm(2)/(V s) at an electric field of 5 × 10(5) V/cm. Density functional theory (DFT) calculations revealed that triplet wave functions were effectively confined and mostly located at either side of the carbazolyl units for m-Cb and p-Cb. Low-temperature PL spectra indeed provided unequivocal data with higher triplet energy (T(1)) of 3.1 eV for both m-Cb and p-Cb. p-Cb was successfully used as a host in deep blue PHOLEDs to provide a high external quantum efficiency of 15.3% and commission internationale de l'elcairage (CIE) coordinates of (0.15, 0.24).

Herein, we present a radical cascade addition cyclization sequence to access quinoline-based benzophosphole oxides from ortho-alkynylated aromatic phosphine oxides using various aryl isonitriles as radical acceptors and inexpensive tert-butyl-hydroperoxide (TBHP) as a terminal oxidant in the presence of a catalytic amount of silver acetate. Alternatively, the same cascade can be realized through a sustainable photochemical approach utilizing 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as an organic photocatalyst at room temperature. The introduced modular approach shows broad functional group tolerance and offers straightforward access to complex P,N-containing polyheterocyclic arenes. These novel π-extended benzophosphole oxides exhibit interesting photophysical and electrochemical properties such as absorption in the visible region, emission and reversible reduction at low potentials, which makes them promising for potential materials science applications. The photophysical properties can further be tuned by the addition of external Lewis and Brønsted acids.

The effect of high dose vanadium ion implantation and pulsed laser annealing on the crystal structure and sub-bandgap optical absorption features of V-supersaturated silicon samples has been studied through the combination of experimental and theoretical approaches. Interest in V-supersaturated Si focusses on its potential as a material having a new band within the Si bandgap. Rutherford backscattering spectrometry measurements and formation energies computed through quantum calculations provide evidence that V atoms are mainly located at interstitial positions. The response of sub-bandgap spectral photoconductance is extended far into the infrared region of the spectrum. Theoretical simulations (based on density functional theory and many-body perturbation in GW approximation) bring to light that, in addition to V atoms at interstitial positions, Si defects should also be taken into account in explaining the experimental profile of the spectral photoconductance. The combination of experimental and theoretical methods provides evidence that the improved spectral photoconductance up to 6.2 µm (0.2 eV) is due to new sub-bandgap transitions, for which the new band due to V atoms within the Si bandgap plays an essential role. This enables the use of V-supersaturated silicon in the third generation of photovoltaic devices.

A series of aggregation-induced emission (AIE) fluorescence probes, coined 4H-pyrimido[2,1-b]benzothiazole derivatives, has been synthesized by Biginelli reactions. Utilizing spectroscopic techniques, their photophysical properties have been comprehensively investigated in working environment both in vitro and in vivo. Density functional theory (DFT) calculations were performed to better understand the mechanism of these probes. The interactions between 4H-pyrimido[2,1-b]benzothiazoles with different substituents and bovine serum albumin (BSA) were analyzed using UV-vis and fluorescence spectroscopy, synchronous fluorescence, and docking analysis. Studies found that 4H-pyrimido[2,1-b]benzothiazole could bind to bovine serum albumin (BSA) through a hydrogen bond and hydrophobic interactions, resulting in enhancement of fluorescence emission of probes 1a-6f and fluorescence quenching of BSA. Combined with cell imaging experiments, these provide information on potential effects of benzothiazoles on disease treatment.

Triphenylamine based bis and tris methoxy and hydroxyl aldehydes, their benzothiazole derivatives and boron complexes were synthesized. Bathochromically shifted keto tautomer emissions were observed for bis and tris hydroxyl aldehyde derivatives in non‐polar solvents such as heptane and toluene while other excited state intramolecular proton transfer (ESIPT) derivatives show only enol emission, where ESIPT effect get suppressed under the increased intramolecular charge transfer (ICT) effect. After boron complexation of ESIPT cores, red shifted emissions with increased quantum yield were reported, implying that the ESIPT compounds are exhibiting only enol emissions and not any keto emissions. We optimized all the derivatives using time dependent density functional theory (TD‐DFT) method and compared their computationally derived photophysical parameters with the experimentally observed ones. Variable twist in the dihedral angle of these compounds in their excited state optimized geometries supported their experimentally observed ICT or ESIPT behaviour.

Synthesis of highly soluble fluorescent π-extended 2-(2-thienyl)benzothiazole derivatives via oxidative cyclization of 2-thienylthioanilide as the key step

Effect of substituted nitrogen atom location on the photophysical and charge transporting properties of carboline derivatives

Two novel bipolar host materials, BCzSCN and BCzSPO, consisting of an electron deficient cyano or diphenylphosphine oxide acceptor linked to a bicarbazole donor, were designed and synthesized. Their thermal, photophysical and electrochemical properties were systematically investigated. Both BCzSCN and BCzSPO show high triplet energies of over 2.75 eV and could be developed for application in blue phosphorescent organic light-emitting diodes (PHOLEDs), and further for white PHOLEDs. Moreover, the characterization of hole-only and electron-only devices based on BCzSCN and BCzSPO indicate their rather balanced hole/electron injection and transport properties. Blue PHOLEDs containing BCzSCN and BCzSPO as the hosts and FIrpic as a dopant exhibited excellent performance, with maximum external quantum efficiencies of 19.3% and 17.1% respectively. In particular, blue PHOLEDs adopting BCzSCN and BCzSPO exhibited extraordinary low efficiency roll-offs of 5.2% and 7.6% at a brightness of 1000 cd m−2, respectively. Meanwhile, the all-phosphor near-white devices hosted by the two materials were also fabricated, and high external quantum efficiencies of 22.0% and 21.3% were achieved.

Synthesis and properties of twin derivatives of triphenylamine and carbazole

Experimental studies and mathematical models are disparate approaches for inferring the stress and strain environment in mammalian jaws. Experimental designs offer accurate, although limited, characterization of biomechanical behavior, while mathematical approaches (finite element modeling in particular) offer unparalleled precision in depiction of strain magnitudes, directions, and gradients throughout the mandible. Because the empirical (experimental) and theoretical (mathematical) perspectives differ in their initial assumptions and their proximate goals, the two methods can yield divergent conclusions about how masticatory stresses are distributed in the dentary. These different sources of inference may, therefore, tangibly influence subsequent biological interpretation. In vitro observation of bone strain in primate mandibles under controlled loading conditions offers a test of finite element model predictions. Two issues which have been addressed by both finite element models and experimental approaches are: (1) the distribution of torsional shear strains in anthropoid jaws and (2) the dissipation of bite forces in the human alveolar process. Not surprisingly, the experimental data and mathematical models agree on some issues, but on others exhibit discordance. Achieving congruence between these methods is critical if the nature of the relationship of masticatory stress to mandibular form is to be intelligently assessed. A case study of functional/mechanical significance of gnathic morphology in the hominid genus Paranthropus offers insight into the potential benefit of combining theoretical and experimental approaches. Certain finite element analyses claim to have identified a biomechanical problem unrecognized in previous comparative work, which, in essence, is that the enlarged transverse dimensions of the postcanine corpus may have a less important role in resisting torsional stresses than previously thought. Experimental data have identified subperiosteal cortical thinning as a culprit in diminishing the role of cross-sectional geometry in conditioning the strain environment. These observations raise questions concerning the biomechanical significance of mandibular form in early hominids, fueling persistent arguments over whether gnathic morphology can be related to dietary specialization in the "robust" australopithecines. Nonmechanical explanations (e.g., tooth size or body size) for Paranthropus mandibular dimensions, however, are not compelling as competing hypotheses. Both theoretical and experimental models are in need of refinement before it is possible to conclude that the jaws of the "robust" australopithecines are not functionally linked to elevated masticatory loads.

To investigate mechanisms of compound-corneocyte interactions in a combined experimental and theoretical approach. Experimental methods are presented to investigate compound-corneocyte interactions in terms of dissolution within water of hydration and protein binding and to quantify the extent of the concurrent mechanisms. Results are presented for three compounds: caffeine, flufenamic acid, and testosterone. Two compartmental stratum corneum models M1 and M2 are formulated based on experimentally determined input parameters describing the affinity to lipid, proteins and water. M1 features a homogeneous protein compartment and considers protein interactions only via intra-corneocyte water. In M2 the protein compartment is sub-divided into a cornified envelope compartment interacting with inter-cellular lipids and a keratin compartment interacting with water. For the non-protein binding caffeine the impact of the aqueous compartment on stratum corneum partitioning is overestimated but is successfully modeled after introducing a bound water fraction that is non-accessible for compound dissolution. For lipophilic, keratin binding compounds (flufenamic acid, testosterone) only M2 correctly predicts a concentration dependence of stratum corneum partition coefficients. Lipophilic and hydrophilic compounds interact with corneocytes. Interactions of lipophilic compounds are probably confined to the corneocyte surface. Interactions with intracellular keratin may be limited by their low aqueous solubility.

The influence of non-covalent σ-π orbital interactions on triplet-triplet energy transfer (TTET) through tuning of the donor excitation energy remains basically unexplored. In the present work, we have investigated intermolecular TTET using donor moieties covalently linked to a rigid cholesterol (Ch) scaffold. For this purpose, diaryl ketones of π,π* electronic configuration tethered to α- or β-Ch were prepared from tiaprofenic acid (TPA) and suprofen (SUP). The obtained systems TPA-α-Ch, TPA-β-Ch, SUP-α-Ch and SUP-β-Ch were submitted to photophysical studies (laser flash photolysis and phosphorescence), in order to delineate the influence of steric shielding and σ-π orbital interactions on the rate of TTET to a series of energy acceptors. As a matter of fact, fine tuning of the donor triplet energy significantly modifies the rate constants of TTET in the absence of diffusion control. The experimental results are rationalized by means of theoretical calculations using first principles methods based on DFT as well as molecular dynamics.