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The potential control of circularly polarized luminescence (CPL), especially its sign and switching at the molecular level without any chemical modification, is desirable, but remains a considerable challenge owing to the difficulty to finely control the magnitude and relative orientation of the associated electric and magnetic dipole transition moments. To address this challenge, we report the synthesis and chiroptical properties of innovative non-conjugated chiral donor–acceptor systems displaying CPL sign inversion as a function of solvent polarity. Through the formation of a chiral exciplex, it is possible to achieve control of its (non-) radiative deexcitation pathways using solvents of different polarity, resulting in emission from locally excited (LE) or charge-transfer (CT) states (with positive and negative CPL), and thermally activated delayed fluorescence (TADF). Theoretical calculations offer further evidence of the relationship between the nature of the emitting species and the CPL. These results provide original molecular design guidelines to obtain switchable CPL emitters, and new insights into the combination of CPL and TADF, a feature of crucial importance for the development of efficient technologies based on CPL emitters. [ABSTRACT FROM AUTHOR]

Synthesis of two dithia[9]helicenes by means of a LED-based double photocyclization is reported. The compounds have sulfur atoms placed at the terminal rings of the helicene, and they display two alternative C2-symmetrical arrangements named exo (1) and endo (2). Separation of enantiomers of opposite helicity allowed the complete characterization in solution, in silico, by X-ray crystallography, and adsorbed on gold. The theoretical analysis confirms the unexpected finding that endo-dithia[9]helicene displays an experimental dissymmetry factor (glum) in CPL larger than its isomer exo-dithia[9]helicene (–0.0125 vs. −0.0042). This enhanced glum factor ranks among the largest for a helicene-type molecule. Comparison with smaller analogues, namely exo and endo-dithia[7]helicenes (10 and 11, respectively), is also presented. [ABSTRACT FROM AUTHOR]

The amount of data and number of databases for the assessment and parameterization of density functional theory methods has grown substantially in the past two decades. In this work, we introduce a novel cluster analysis technique for density functional theory calculations of the electronic structure of atoms and molecules with the goal of creating new statistically significant databases with broad chemical scope, and a manageable number of data-points. By analyzing without a priori chemical assumptions a population of almost 350k data-points, we create a new database called ASCDB containing only 200 data-points. This new database holds the same chemical information as the larger population of data from which it is obtained, but with a computational cost that is reduced by several orders of magnitude. The labelling of the significant chemical properties is performed a posteriori on the resulting 16 subsets, classifying them into four areas of chemical importance: non-covalent interactions, thermochemistry, non-local effects, and unbiased calculations. The analysis of the results and their transferability shows that ASCDB is capable of providing the same information as that of the larger collection of data—such as GMTKN55, MGCDB84, and Minnesota 2015B—for several density functional theory methods and basis sets. In light of these results, we suggest the use of this new small database as a first inexpensive tool for the evaluation and parameterization of electronic structure theory methods. [ABSTRACT FROM AUTHOR]