Coumarins often function in the solution phase for a diverse range of optoelectronic applications. The associated solvent effects on the UV–vis absorption and/or fluorescence spectral shifts of coumarins need to be understood in order that their photochemistry can be controlled. To this end, three different empirical solvatochromic models are assessed against 13 coumarins. The two generalized solvent scales developed by Catalán and co-workers demonstrate comparable performance to the popular Taft–Kamlet solvatochromic comparison method. A combinatorial approach to determine the best-fit equations in all of the empirical models is applied; this involves both statistical best-fits and the physical validation of the resulting parameters, based on the molecular structures of solvents and solutes and their corresponding interactions. The findings of this approach are used to extract useful information about different aspects of solvent effects on the solvatochromism of coumarins.

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.

We report photoexcited-state crystal structures for two new members of the ͓Ru͑SO 2 ͒͑NH 3 ͒ 4 X͔Y family: 1 : X =H 2 O, Y = ͑ Ϯ ͒-camphorsulfonate 2 ; 2 : X = isonicotinamide, Y = tosylate 2 . The excited states are metastable at 100 K, with a photoconversion fraction of 11.1͑7͒% achieved in 1, and 22.1͑10͒% and 26.9͑10͒% at the two distinct sites in 2. We further show using solid-state density-functional-theory calculations that the excited-state geometries achieved are strongly influenced by the local crystal environment. This result is relevant to attempts to rationally design related photoexcitation systems for optical data-storage applications.

A major deficit in suitable dyes is stifling progress in the dye-sensitised solar cell (DSC) industry. Materials discovery strategies have afforded numerous new dyes; yet, corresponding solution-based DSC device performance has little improved upon 11% efficiency, achieved using the N719 dye over two decades ago. Research on these dyes has nevertheless revealed relationships between the molecular structure of dyes and their associated DSC efficiency. Here, such structure-property relationships have been codified in the form of molecular dye design rules, which have been judiciously sequenced in an algorithm to enable large-scale data mining of dye structures with optimal DSC performance. This affords, for the first time, a DSC-specific dye-discovery strategy that predicts new classes of dyes from surveying a representative set of chemical space. A lead material from these predictions is experimentally validated, showing DSC efficiency that is comparable to many well-known organic dyes. This demonstrates the power of this approach.

The photoinduced O-bound coordination mode in RuSO(2) complexes, previously observed only at 13 K, has been generated at 100 K in tetraammineaqua(sulfur dioxide)ruthenium(II) (±)-camphorsulfonate. This coordination state, often denoted MS1, decays to the η(2)-bound MS2 state, with an estimated half-life of 3.4(8) h and a long-lived population of 2.9(4)% at 120 K.