20th World wind energy conference & exhibition. WEEC 2022

This paper represents a preface to the Proceedings of the 20th World Wind Energy Conference & Exhibition (WEEC 2022) held in Rimini, Italy, from the 28th to the 30th of June 2022. Background information, conference resolution and the organizational structure of the meeting, program committee, and acknowledgments of the contributions of the many people who made the conference a success are presented

Sequential FRET processes in calix[4]arene-linked orange-red-green perylene bisimide dye zigzag arrays

Perylene bisimide-calix[4]arene arrays composed of up to three different types of perylene bisimide chromophores (orange, red, and green PBIs) have been synthesized. Within these arrays, the individual chromophoric building blocks are positioned in defined spatial orientation and are easily replaceable by each other without influencing the overall geometric arrangement of the supramolecular system. The specific optical properties of the individual chromophore facilitated the investigation of photoinduced processes very accurately by time-resolved emission and femtosecond transient absorption spectroscopy. A quantitative analysis of the photophysical processes as well as their rate constants have been obtained by employing UV/vis absorption, steady state and time-resolved emission, femtosecond transient absorption spectroscopy, and spectrotemporal analysis of the femtosecond transient absorption data. These studies reveal very efficient energy transfer processes from the orange to the red PBI chromophoric unit (k(ET) = 6.4 x 10(11) s(-1) for array or), from the red to the green PBI (k(ET) = 4.0 x 10(11) s(-1) for array rg), and slightly less efficient from the orange to the green PBI (k(ET) = 1.5 x 10(11) s(-1) for array og) within these perylene bisimide-calix[4]arene arrays. The experimentally obtained rate constants for the energy transfer processes are in very good agreement with those calculated according to the Forster theory

Crystal engineering rescues a solution organic synthesis in a cocrystallization that confirms the configuration of a molecular ladder

Treatment of an achiral molecular ladder of C2h symmetry composed of five edge-sharing cyclobutane rings, or a [5]-ladderane, with acid results in cis- to trans-isomerization of end pyridyl groups. Solution NMR spectroscopy and quantum chemical calculations support the isomerization to generate two diastereomers. The NMR data, however, could not lead to unambiguous configurational assignments of the two isomers. Single-crystal X-ray diffraction was employed to determine each configuration. One isomer readily crystallized as a pure form and X-ray diffraction revealed the molecule as being achiral based on Ci symmetry. The second isomer resisted crystallization under a variety of conditions. Consequently, a strategy based on a cocrystallization was developed to generate single crystals of the second isomer. Cocrystallization of the isomer with a carboxylic acid readily afforded single crystals that confirmed a chiral ladderane based on C2 symmetry. The chiral ladderane and acid self-assembled to generate a five-component hydrogen-bonded complex that packs to form large solvent-filled homochiral channels of nanometer-scale dimensions. Whereas cocrystallizations are frequently applied to structure determinations of proteins, our study represents the first application of a cocrystallization to confirm the relative configuration of a small-molecule diastereomer generated in a solution-phase organic synthesis