Coumarin derivatives are used in a wide range of applications, such as dye-sensitized solar cells (DSCs) and dye lasers, and have therefore attracted considerable research interest. In order to understand the molecular origins of their optoelectronic properties, molecular structures for 29 coumarin laser dyes are statistically analyzed. To this end, data for 25 compounds were taken from the Cambridge Structural Database and compared with data for four new crystal structures of coumarin laser dyes [Coumarin 487 (C(19)H(23)NO(2)), Coumarin 498 (C(16)H(17)NO(4)S), Coumarin 510 (C(20)H(18)N(2)O(2)), and Coumarin 525 (C(22)H(18)N(2)O(3))], which are reported herein. The competing contributions of different resonance states to the bond lengths of the 4- and 7-substituted coumarin laser dyes are computed based on the harmonic oscillator stabilization energy model. Consequently, a positive correlation between the contribution of the para-quinoidal resonance state and the UV-vis peak absorption wavelength of these coumarins is revealed. Furthermore, the perturbations of optoelectronic properties, owing to chemical substituents in these coumarin laser dyes, are analyzed: it is found that their UV-vis peak absorption and lasing wavelengths experience a red shift, as the electron-donating strength of the 7-position substituent increases and/or the electron-withdrawing strength of the 3- or 4-position substituent rises; this conclusion is corroborated by quantum-chemical calculations. It is also revealed that the closer the relevant substituents align with the direction of the intramolecular charge transfer (ICT), the larger the spectral shifts and the higher the molar extinction coefficients of coumarin laser dyes. These findings are important for understanding the ICT mechanism in coumarins. Meanwhile, all structure-property correlations revealed herein will enable knowledge-based molecular design of coumarins for dye lasers and DSC applications.

Summary Single-crystal X-ray diffraction analysis (SCXRD) constitutes a universal approach for the elucidation of molecular structure and the study of crystalline forms. However, the discovery of viable crystallization conditions remains both experimentally challenging and resource intensive in both time and the quantity of analyte(s). We report a robot-assisted, high-throughput method for the crystallization of organic-soluble small molecules in which we employ only micrograms of analyte per experiment. This allows hundreds of crystallization conditions to be screened in parallel with minimal overall sample requirements. Crystals suitable for SCXRD are grown from nanoliter droplets of a solution of analyte in organic solvent(s), each of which is encapsulated within an inert oil to control the rate of solvent loss. This encapsulated nanodroplet crystallization methodology can also be used to search for new crystal forms, as exemplified through both our discovery of a new (13 th ) polymorph of the olanzapine precursor ROY and SCXRD analysis of the “uncrystallizable” agrochemical dithianon.

Three new ruthenium-sulfur dioxide linkage photoisomeric complexes in the [Ru(NH(3))(4)(SO(2))X]Cl(2)·H(2)O family (X = pyridine (1); 3-chloropyridine (2); 4-chloropyridine (3)) have been developed in order to examine the effects of the trans-ligand on the nature of the photo-induced SO(2) coordination to the ruthenium ion. Solid-state metastable η(1)-O-bound (MS1) and η(2)-side S,O-bound (MS2) photoisomers are crystallographically resolved by probing a light-induced crystal with in situ diffraction. This so-called photocrystallography reveals the highest known photoconversion fraction of 58(3)% (in 1) for any solid-state SO(2) linkage photoisomer. The decay of this MS1 into the MS2 state was modeled via first-order kinetics with a non-zero asymptote. Furthermore, the MS2 decay kinetics of the three compounds were examined according to their systematically varying trans-ligand X; this offers the first experimental evidence that the MS2 state is primarily stabilized by donation from the S-O(bound) electrons into the Ru dσ-orbital rather than π-backbonding as previously envisaged. This has important consequences for the optoelectronic application of these materials since this establishes, for the first time, a design protocol that will enable one to control their photoconversion levels.

Helically chiral N,N,O,O‐boron chelated dipyrromethenes showed solution‐phase circularly polarized luminescence (CPL) in the red region of the visible spectrum (λ em(max) from 621 to 663 nm). The parent dipyrromethene is desymmetrised through O chelation of boron by the 3,5‐ortho‐phenolic substituents, inducing a helical chirality in the fluorophore. The combination of high luminescence dissymmetry factors (|g lum| up to 4.7 ×10−3) and fluorescence quantum yields (Φ F up to 0.73) gave exceptionally efficient circularly polarized red emission from these simple small organic fluorophores, enabling future application in CPL‐based bioimaging.

The relationship between the molecular structures of a series of azo dyes and their operational performance when applied to dye-sensitized solar cells (DSSCs) is probed via experimental and computational analysis. Seven azo dyes, with three different donating groups (dimethylamino, diethylamino, and dipropylamino) and carboxylic acid anchoring positions (ortho-, meta-, and para-substituted phenyl rings) are studied. Single-crystal X-ray diffraction is employed in order to analyze the effects of conformation and quantify the contribution of quinoidal resonance forms to the intramolecular charge transfer (ICT), which controls their intrinsic photovoltaic potential from an electronic standpoint. Harmonic oscillator stabilization energy (HOSE) calculations indicate that the para- and ortho-azo dyes exhibit potential for DSSC application. However, from a geometrical standpoint, the crystal structure data, proton nuclear magnetic resonance spectroscopy (1H NMR), and density functional theory (DFT) all indicate that intramolecular hydrogen bonds form in ortho-dyes within both solid and solution states, impeding their intrinsic ICT-based photovoltaic potential, and offering insights into the photostability of azo dyes and the dye···TiO2 anchoring mechanism in DSSCs. Donor effects are manifested in the packing mode and molecular planarity revealed by X-ray crystallography and in the UV/vis absorption spectra. DFT and time-dependent density functional theory (TDDFT) were performed to understand the electronic and optical properties of these azo dyes; these calculations compare well with experimental findings. Operational tests of DSSCs, functionalized by these azo dyes, show that the carboxylic acid anchoring position plays a crucial role in DSSC performance, while donating groups offer a much less obvious effect on the overall DSSC device efficiency.