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2,7-Bis(2-phenyl-1H-imidazol-4-yl)fluorenone (BPIFO) was synthesized as a new fluorenone derivative bearing two imidazole moieties, and it exhibited remarkable and reversible changes in photo physi...

Collaborative robots have to adapt its motion plan to a dynamic environment and variation of task constraints. Currently, they detect collisions and interrupt or postpone their motion plan to prevent harm to humans or objects. The more advanced strategy proposed in this article uses online trajectory optimization to anticipate potential collisions, task variations, and to adapt the motion plan accordingly. The online trajectory planner pursues a model predictive control approach to account for dynamic motion objectives and constraints during task execution. The prediction model relates reference joint velocities to actual joint positions as an approximation of built-in robot tracking controllers. The optimal control problem is solved with direct collocation based on a hypergraph structure, which represents the nonlinear program and allows to efficiently adapt to structural changes in the optimization problem caused by moving obstacles. To demonstrate the effectiveness of the approach, the robot imitates pick-and-place tasks while avoiding self-collisions, semistatic, and dynamic obstacles, including a person. The analysis of the approach concerns computation time, constraint violations, and smoothness. It shows that after model identification, order reduction, and validation on the real robot, parallel integrators with compensation for input delays exhibit the best compromise between accuracy and computational complexity. The model predictive controller can successfully approach a moving target configuration without prior knowledge of the reference motion. The results show that pure hard constraints are not sufficient and lead to nonsmooth controls. In combination with soft constraints, which evaluate the proximity of obstacles, smooth and safe trajectories are planned., Optimal control applications and methods;Vol. 41. 2020, issue 4, pp 1211-1232

Online trajectory planning allows robotic manipulators to adapt to changing environments and dynamic tasks, which becomes increasingly relevant through human-robot interaction. optimizing motion objectives is a common way of planning but is usually conducted in joint space, whereas many planning objectives are rather defined in task space. Joint Space Planning (JSP) first transforms target poses into joint space and then performs conventional optimization. Implicit Task Space Planning (ITSP) uses a special objective function to directly consider task quantities and is similar to economic model predictive control. Remarkably, comparative studies of both approaches with respect to their performance are scarce. This contribution aims at filling this gap by providing a systematic analysis of both methods using a 6-DoF collaborative robot in practical experiments. Results show that the first method is less sensitive to local minima and profits from active reconfiguration abilities while it generates less straight-lined motions and is not able to account for target manifolds in the task space. The second method can easily consider target manifolds and performs more straight-lined motions while it is more sensitive to local minima and provides active reconfiguration only partially. Although the cost function of the second method is significantly more complex, the computational effort relativizes during planning.

Water-soluble distyrylbenzene-based aldehydes are excellent fluorescence turn-on indicators for amine detection, since they are themselves non-fluorescent in water. Here, the fluorescence quenching mechanisms of aldehydes with systematically increasing π -systems are investigated in an aqueous environment using quantum chemical methods. Although the aldehydes are structurally related, with each extension of the π -system the fluorescence quenching mechanism changes from excited-state hydrogen transfer to trans→cis isomerization and n π ∗ state-mediated intersystem crossing, until the aldehydes become fluorescent in water. For distyrylbenzene aldehyde, n π ∗ mediated ISC has been identified as major fluorescence quenching channel, which becomes closed upon reaction with an amine explaining its fluorescence turn-on sensitivity.

The synthesis of a doubly bridged tolane is reported. The target is obtained in a five-step synthesis, starting from commercially available 2-amino-meta-xylene by a combination of a Sandmeyer reaction, radical bromination, and Stille-type coupling, followed by double ring closing. The doubly tethered tolane is crystalline; the two phenyl rings are highly twisted with respect to each other both in solution and in the solid state. Optical spectroscopy and quantum chemical calculations show that the doubly bridged tolane is twisted not only in the ground state, but also in the excited state, leading to emission from the twisted state in solution and in the solid state. Strong phosphorescence is observed at cryogenic temperatures.

Aufgrund der Moglichkeit mit nur einer Maschine Beton gezielt uber weite Strecken zu befordern, sind auf Baustellen haufig mobile Autobetonpumpen im Einsatz. Der Mastaufbau dieser Grosraummanipulatoren wird derzeit manuell von einem Maschinisten durchgefuhrt, der aufgrund der hohen Reichweiten und Sicherheitsabstande die Gelenke tendenziell sequenziell bedient. Wegen des geringen Platzangebots auf Baustellen konnen platzsparende Teilabstutzungen verwendet werden, bei denen zur Gewahrleistung der Standsicherheit derzeit fest vorgegebene und langsame Ausfaltphasen vom Maschinisten zu befolgen sind. Die manuelle Bedienung und die vorgegebenen Ausfaltphasen fuhren dazu, dass der Ausfaltvorgang des Masts aktuell ungefahr $$39\,\%$$ der Aufbauphase einnimmt. Im vorliegenden Beitrag wird zur Reduzierung der Ausfaltzeit eine modellpradiktive Regelung fur den automatisierten und zeitoptimalen Mastaufbau einer mobilen Autobetonpumpe unter den Nebenbedingungen der Standsicherheit, Volumenstrombeschrankungen und Vermeidung von Selbstkollisionen realisiert. Durch die Analyse simulierter Ausfaltvorgange in verschiedene Zielkonfigurationen und den Vergleich zu manuellen Ausfaltungen werden der modellpradiktive Regler verifiziert und das zunachst theoretische Einsparpotential des automatisierten Mastaufbaus aufgezeigt.

The synthesis and optical properties of several novel fluorescent and/or phosphorescent bridged tolanes (tolanophanes) are reported and their optical and structural properties are investigated. Specifically, diiodinated and bisalkynylated tolanophanes were obtained, and characterized by spectroscopy and computational methods. They represent attractive building blocks for novel polymers and emissive solid-state materials.

The rotational motion of tolanes along their acetylene axis is not fully understood. What happens to the optical and electronic properties if the tolane backbone is forced into a twisted conformation? Several tethers were investigated to obtain tolanophanes, fixing the torsion angle of the two phenyl rings. X-ray crystal structures revealed tether-specific torsion angles in the solid state. The absorption, emission, and excitation spectra were recorded. Twisted tethered tolane conformers showed blue-shifted absorption; emission spectra were all torsionally independent and identical. The tethered tolanes were embedded in a rigid matrix by freezing to 77 K; well-resolved emission spectra were recorded for planar tolanes, but for twisted systems unexpectedly long-lived phosphorescence was observed. How is this triplet emission explained? Quantum chemical calculations (TDDFT/cam-B3LYP/6-31G*) of the unsubstituted tolane showed that intersystem crossing (ISC) is favored with large spin-orbit coupling, which occurs when the molecular orbitals are orthogonal to each other; this is the case at the crossing of S1/T7. Also, a small energy difference between singlet and triplet states is required; we found that ISC can favorably take place at four crossings: S1/T6, S1/T7, S1/T(8,9), S1/T10.

Influencing the communication within a conjugated system as diphenylacetylene is a challenging subject in molecular electronics. Some examples of twisted tolanes are known, where high twists have been achieved in the solid state by steric encumbrance. The insertion of a spacer system is an alternative way to tailor rotation. Only a few examples of such tethered tolanes exist, and they all suffer from small twist angles (