Accessing the triplet state of perylenediimide by radical-enhanced intersystem crossing.

Owing to their exceptional photophysical properties and high photostability, perylene diimide (PDI) chromophores have found various applications as building blocks of materials for organic electronics. In many light-induced processes in PDI derivatives, chromophore excited states with high spin multiplicities, such as triplet or quintet states, have been revealed as key intermediates. The exploration of their properties and formation conditions is thus expected to provide invaluable insight into their underlying photophysics and promises to reveal strategies for increasing the performance of optoelectronic devices. However, accessing these high-multiplicity excited states of PDI to increase our mechanistic understanding remains a difficult task, due to the fact that the lowest excited singlet state of PDI decays with near-unity quantum yield to its ground state. Here we make use of radical-enhanced intersystem crossing (EISC) to generate the PDI triplet state in high yield. One or two 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) stable radicals were covalently attached to the imide position of PDI chromophores with and without p-tert-butylphenoxy core substituents. By combining femtosecond UV-vis transient absorption and transient electron paramagnetic resonance spectroscopies, we demonstrate strong magnetic exchange coupling between the PDI triplet state and TEMPO, resulting in the formation of excited quartet or quintet states. Important differences in the S1 state deactivation rate constants and triplet yields are observed for compounds bearing PDI moieties with different core substitution patterns. We show that these differences can be rationalized by considering the varying importance of competitive excited state decay processes, such as electron and excitation energy transfer. The comparison of the results obtained for different PDI-TEMPO derivatives leads us to propose design guidelines for optimizing the efficiency of triplet sensitization in molecular assemblies by EISC.

Syntheses of three-dimensional catenanes under kinetic control.

Although catenanes comprising two ring-shaped components can be made in large quantities by templation, the preparation of three-dimensional (3D) catenanes with cage-shaped components is still in its infancy. Here, we report the design and syntheses of two 3D catenanes by a sequence of SN2 reactions in one pot. The resulting triply mechanically interlocked molecules were fully characterized in both the solution and solid states. Mechanistic studies have revealed that a suit[3]ane, which contains a threefold symmetric cage component as the suit and a tribromide component as the body, is formed at elevated temperatures. This suit[3]ane was identified as the key reactive intermediate for the selective formation of the two 3D catenanes which do not represent thermodynamic minima. We foresee a future in which this particular synthetic strategy guides the rational design and production of mechanically interlocked molecules under kinetic control.

Effect of the Time Delay between Spin State Preparation and Measurement on Electron Spin Teleportation in a Covalent Donor-Acceptor-Radical System.

We recently demonstrated photodriven quantum teleportation of an electron spin state in a covalent donor-acceptor-radical (D-A-R•) system. Following specific spin state preparation on R• with a microwave pulse, photoexcitation of A results in two-step electron transfer producing D•+-A-R-, where the spin state on R• is teleported to D•+. This study examines the effects of varying the time (τD) between spin state preparation and photoinitiated teleportation. Using pulse electron paramagnetic resonance spectroscopy, the spin echo of D•+ resulting from teleportation shows a damped oscillation as a function of τD that is simulated using a density matrix model, which provides a fundamental understanding of the echo behavior. Teleportation fidelity calculations also show oscillatory behavior as a function of τD due to the accumulation of a phase factor between ⟨Sx⟩ and ⟨Sy⟩. Understanding experimental parameters intrinsic to quantum teleportation in molecular systems is crucial to leveraging this phenomenon for quantum information applications.

Charge Transfer and Spin Dynamics in a Zinc Porphyrin Donor Covalently Linked to One or Two Naphthalenediimide Acceptors.

Quantum coherence effects on charge transfer and spin dynamics in a system having two degenerate electron acceptors are studied using a zinc 5,10,15-tri(n-pentyl)-20-phenylporphyrin (ZnP) electron donor covalently linked to either one or two naphthalene-1,8:4,5-bis(dicarboximide) (NDI) electron acceptors using an anthracene (An) spacer, ZnP-An-NDI (1) and ZnP-An-NDI2 (2), respectively. Following photoexcitation of 1 and 2 in toluene at 295 K, femtosecond transient absorption spectroscopy shows that the electron transfer (ET) rate constant for 2 is about three times larger than that of 1, which can be accounted for by the statistical nature of incoherent ET as well as the electron couplings for the charge separation reactions. In contrast, the rate constant for charge recombination (CR) of 1 is about 25% faster than that of 2. Using femtosecond transient infrared spectroscopy and theoretical analysis, we find that the electron on NDI2•- in 2 localizes onto one of the two NDIs prior to CR, thus precluding electronically coherent CR from NDI2•-. Conversely, CR in both 1 and 2 is spin coherent as indicated by the observation of a resonance in the 3*ZnP yield following CR as a function of applied magnetic field, giving spin-spin exchange interaction energies of 2J = 210 and 236 mT, respectively, where the line width of the resonance for 2 is greater than 1. These data show that while CR is a spin-coherent process, incoherent hopping of the electron between the two NDIs in 2, consistent with the lack of delocalization noted above, results in greater spin decoherence in 2 relative to 1.

Glossary of terms for musculoskeletal radiology.

Members of the International Skeletal Society compiled a glossary of terms for musculoskeletal radiology. The authors also represent national radiology or pathology societies in Asia, Australia, Europe, and the USA. We provide brief descriptions of musculoskeletal structures, disease processes, and syndromes and address their imaging features. Given the abundance of musculoskeletal disorders and derangements, we chose to omit most terms relating to neoplasm, spine, intervention, and pediatrics. Consensus agreement was obtained from 19 musculoskeletal radiology societies worldwide.

Highlights of the annual scientific meeting of the Society of Skeletal Radiology (SSR) 2019, Scottsdale, Arizona, USA.

Peer-reviewed abstracts presented at the 2019 Society of Skeletal Radiology (SSR) Annual Meeting were reviewed following oral presentation. Topics felt to be of potential interest to musculoskeletal (MSK) investigators and practicing clinicians are highlighted in this compilation and analysis of the meeting. New concepts regarding MSK imaging and intervention, MSK protocols and techniques, and quality improvement are included. ePoster highlights are also presented.

Acute Shoulder Injury.

Acute shoulder injury is commonly encountered by clinicians, surgeons, and radiologists. A comprehensive evaluation of the shoulder by the radiologist is essential to accurately relay findings that have a direct impact on acute and long-term management. In this review, imaging features of acute injuries involving the proximal humerus, glenohumeral joint, rotator cuff, tendon of the long head of the biceps brachii, and acromioclavicular joint are discussed. Modalities include ultrasound examination, conventional radiography, computed tomography scans, and MR imaging. Emphasis is placed on radiographic features that have an impact on patient management.

Standard and Advanced Imaging of Hip Osteoarthritis. What the Radiologist Should Know.

Osteoarthritis (OA) of the hip is caused by degeneration of articular cartilage and the underlying bone and can be divided into two types: primary (associated with advancing age) and secondary (subsequent to fractures, avascular necrosis, infection, developmental dysplasia, and femoroacetabular impingement). Radiography remains the first-line imaging modality for diagnosing and monitoring OA, due to its accessibility, low cost, and ease of interpretation. Kellgren-Lawrence and Tönnis classification systems are radiographic OA grading systems used primarily in research, and they reflect the degree of joint space narrowing, sclerosis, cysts, deformity of the femoral head and acetabulum, and osteophytes. Unenhanced computed tomography (CT) provides detailed visualization of the hip joint segments that may be difficult to appreciate on radiographs, such as the inferoposterior and posterolateral hip joint. CT arthrography, magnetic resonance imaging (MRI), and magnetic resonance arthrography with two-dimensional reconstructions can delineate labral abnormalities, cartilage lesions, and other intra-articular hip pathology. T2 and T2* mapping, delayed gadolinium-enhanced MRI of cartilage, T1rho, ultra-short echo time, and zero echo time are investigative MR techniques with promising evaluation of hip OA.

Postoperative Imaging of Sarcomas.

OBJECTIVE: The purpose of this article is to assist radiologists in developing an organized, systematic approach to imaging interpretation in the care of patients who have been surgically treated for sarcoma. CONCLUSION: Postoperative imaging interpretation of sarcoma can be complex and requires an organized, systematic approach that includes review of the patient's clinical and surgical history and pretreatment images to gain context for differentiating recurrence from time-dependent posttreatment changes.

Society of Skeletal Radiology 2017 annual meeting summary.

Peer-reviewed abstracts presented at the 2017 Society of Skeletal Radiology (SSR) Annual Meeting were reviewed following oral presentation. Topics felt to be of potential interest to musculoskeletal (MSK) investigators and practicing clinicians are highlighted in this compilation and analysis of the meeting. New concepts regarding MSK imaging and intervention, MSK protocols and techniques and quality improvement are included. ePoster highlights are also presented.

Academic musculoskeletal radiology: influences for gender disparity.

INTRODUCTION: Research productivity is one of the few quintessential gauges that North American academic radiology departments implement to determine career progression. The rationale of this study is to quantify the relationship of gender, research productivity, and academic advancements in the musculoskeletal (MSK) radiology to account for emerging trends in workforce diversity. METHODS: Radiology residency programs enlisted in the Fellowship and Residency Electronic Interactive Database (FREIDA), Canadian Resident Matching Service (CaRMS) and International Skeletal Society (ISS) were searched for academic faculty to generate the database for gender and academic profiles of MSK radiologists. Bibliometric data was collected using Elsevier's SCOPUS archives, and analyzed using Stata version 14.2. RESULTS: Among 274 MSK radiologists in North America, 190 (69.34%) were men and 84 (30.66%) were women, indicating a statistically significant difference (χ2 = 6.34; p value = 0.042). The available number of female assistant professors (n = 50) was more than half of the male assistant professors (n = 88), this ratio however, plummeted at higher academic ranks, with only one-fourth of women (n = 11) professors compared to men (n = 45). The male MSK radiologist had 1.31 times the odds of having a higher h-index, keeping all other variables constant. CONCLUSIONS: The trend of gender disparity exists in MSK radiology with significant underrepresentation of women in top tiers of academic hierarchy. Even with comparable h-indices, at the lower academic ranks, a lesser number of women are promoted relative to their male colleagues. Further studies are needed to investigate the degree of influence research productivity has, in determining academic advancement of MSK radiologists.

Regioselective Synthesis, NMR, and Crystallographic Analysis of N1-Substituted Pyrazoles.

A systematic study of the N-substitution reactions of 3-substituted pyrazoles under basic conditions has been undertaken. Regioselective N1-alkylation, -arylation, and -heteroarylation of 3-substituted pyrazoles have been achieved using K2CO3-DMSO. The regioselectivity is justified by the DFT calculations at the B3LYP/6-31G**(d) level. A consistent steric effect on chemical shift has been observed for N-alkyl pyrazole analogues. Twenty-five X-ray crystallographic structures have been obtained to confirm the regiochemistry of the major products.