Time-dependent density functional theory (TDDFT) modelling of Pechmann dyes: from accurate absorption maximum prediction to virtual dye screening.

The red Pechmann dye (λ(max) = 550 nm) is the exo-dimer of 4-phenyl-3-butenolide connected at the α-carbon by a double bond in a trans-fashion. The ring system is easily rearranged to the trans-endo-fused bicyclic 6-membered lactone dimer (yellow). Both lactones can be singly or doubly amidated with primary amines leading to further colour changes. The nature of the core heterocycle (exo- vs. endo-; 5- or 6-membered ring), core heteroatom (O vs. N) and additional substituents on the phenyl ring allows for exquisite control over colour achievable within a single dye family. Herein we present a detailed investigation of the modelling of the electronic spectra of the Pechmann dye family by time-dependent density functional theory (TDDFT). Whereas pure Hartree-Fock (TDHF) ab-initio calculation underestimates the UV/Vis absorption maximum, pure TDDFT leads to a large overestimation. The accuracy of the prediction is highly dependent on the mix of HF and DFT, with BMK (42% HF) and M06-2X (54% HF) giving the closest match with the experimental value. Among all basis sets evaluated, the computationally-efficient, DFT-optimized DGDZVP showed the best chemical accuracy/size profile. Finally, the dispersion interaction-corrected (SMD) implicit solvation model was found to be advantageous compared to the original IEFPCM. The absorption maxima of substituted Pechmann dyes and their rearranged lactone counterparts can be predicted with excellent accuracy (±6 nm) at the optimal SMD(toluene)/TD-BMK/DGDZVP//SMD(toluene)B3LYP/DGDZVP level of theory. Using this procedure, a small virtual library of novel, heterocycle-substituted Pechmann dyes were screened. Such substitution was shown to be a viable strategy for colour tuning, giving λ(max) from 522 (4-pyridyl) to 627 (2-indolyl) nm.

Thiophene-containing Pechmann dyes and related compounds: synthesis, and experimental and DFT characterisation.

Attaching 2-thienyl residues to the Pechmann dye core chromophore (5,5-exo-dilactone situated around a C-C double bond) results in a novel magenta-coloured compound (UV/Vis spectroscopy λ(max) =570 nm in CHCl(3)), which can be rearranged to a yellow 6,6-endo-dilactone (λ(max) =462 nm in CHCl(3)). Single and double amidation results in pronounced redshift in the 5,5-exo series (violet, λ(max) =570 nm and blue, λ(max) =606 nm in CHCl(3), respectively) but pronounced blueshift in the 6,6-endo series (yellow, λ(max) =424 nm and pale yellow bordering on colourless, λ(max) =395 nm in CHCl(3), respectively). Incorporation of a 3-alkyl substituent on the thiophene ring allows for sharp increase of solubility in organic solvents concomitant with fine-tuning of the colour: a redshift in 5,5-exo-dilactones but a blueshift in 5,5-exo-dilactams. DFT computations demonstrate that both lactone classes are planar regardless of the presence of a 3-alkyl group. The lactam derivatives are non-planar: the thiophene-core chromophore dihedral angles increase on going from 5,5-exo to 6,6-endo and from thiophene to 3-alkyl thiophene. Depending on the core heteroatom (O vs. N-alkyl), ring junction (5,5-exo vs. 6,6-endo) and 3-thiophene substituent (H vs. alkyl), two, three, four or six conformers are possible. All of these conformers were characterised by DFT and were found to be very close in energy at both IEFPCM/B3LYP/DGDZVP and SMD/M06/DGDZVP levels of theory. Within each conformer set, the HOMO and LUMO energies were within 0.05 eV and the predicted λ(max) values (TD-DFT) within 10 nm, and this implies low sensitivity of the optical and electronic properties to conformation. Cyclic voltammetry measurements of selected compounds demonstrated good matching to the HOMO and LUMO energies from IEFPCM/B3LYP/DGDZVP computations. M06-2X was the best DFT functional for TD-DFT, giving predicted λ(max) values within about 20 nm.

O,O'-Disubstituted N,N'-dihydroxynaphthalenediimides (DHNDI): first principles designed organic building blocks for materials science.

N,N'-Disubstituted naphthalenediimides (NDIs), planar, electron-deficient building blocks, play an important role in materials and biological sciences. Naphthalene core substituents control the HOMO and LUMO energies, whereas the N-alkyl or aryl substituents affect the solubility, aggregation, and packing propensity in condensed phases. N,N'-Dihydroxynaphthalenediimide (DHNDI) allows expanding the chemical diversity by O-alkylation, acylation, or sulfonylation; these derivatives also allow fine-tuning of the HOMO/LUMO levels. The synthesis, UV-vis, electrochemical, solid state, and computational prediction of the properties of such derivatives are presented.

Thiophene-containing Pechmann dye derivatives.

Thiophene-containing Pechmann dyes (unsaturated exo-5,5-dilactones) were easily prepared by Cu-catalyzed dehydration of the corresponding ß-aroylacrylic acids. Introduction of long alkyl chains greatly enhances solubility. Isomerization of an alkyl-substituted thiophene Pechmann dye (TPD) gave the corresponding endo-6,6-dilactone. The redox and electronic properties of these new dyes were investigated by CV, UV/vis, and fluorescence spectroscopy and DFT and TD-DFT computations. Strong absorption and emission in the visible region were recorded.

Aqueous solubilization of photochromic compounds by bile salt aggregates.

Bile salts form aggregates in aqueous solutions which were shown to efficiently solubilize aqueous insoluble photochromic compounds. Photochromic switching was observed for a spiropyran and a diarylethene. In the case of the spiropyran, the incorporation into the bile salt aggregate led to improved hydrolytic stability and changes in thermal rate constants.

Stimuli responsive surfaces through recognition-mediated polymer modification.

Specific three-point hydrogen bonding between diamidopyridine (DAP) and thymine (Thy) was employed to reversibly anchor "brush-like" Tri-DAP end-functionalized polystyrene onto Thy-modified silica surfaces.

Chiral discrimination in photochromic helicenes.

A photoresponsive dithienylethene derivative bearing chiral pinene-based arms underwent a stereoselective photoinduced cyclization reaction to produce greater than 98% of a single diastereomer. The magnitude of the optical rotation changed as much as Delta[alpha]373 = 8698 degrees upon alternate irradiation with 400 nm and greater than 434 nm light.

Adsorption/desorption of mono- and diblock copolymers on surfaces using specific hydrogen bonding interactions.

Diblock copolymers containing recognition units designed to participate in specific three-point hydrogen bonding were adsorbed onto modified gold surfaces. Self-assembled monolayers (SAMs) containing complementary recognition units were used to direct the adsorption process. The polymer-modified surfaces obtained were characterized using X-ray photoelectron spectroscopy, water contact angle, and ellipsometry. The role of individual block lengths on the adsorption process was followed by observing frequency changes of thymine-SAM-modified quartz crystal microbalance chips during adsorption of diamidopyridine-functionalized polymers from a nonpolar solvent. The renewable nature of these recognition unit functionalized surfaces was demonstrated by reversible binding of polymers. Adsorption onto fresh surfaces, followed by desorption and subsequent readsorption of monoblock and diblock copolymers was also investigated.

Specific Hydrogen-Bond-Mediated Recognition and Modification of Surfaces Using Complementary Functionalized Polymers.

Specific hydrogen-bonding interactions between polymers and surface-tethered recognition elements were used to selectively modify self-assembled monolayers (SAMs) on gold. The interfacial recognition processes were followed by observing frequency changes of thymine-SAM modified quartz crystal microbalance (QCM) chips during adsorption of diamidopyridine-functionalized (DAP) polystyrene from a nonpolar solvent. QCM studies combined with X-ray photoelectron spectroscopy (XPS), water contact angle, and ellipsometry measurements of the polymer-modified surfaces demonstrate the selectivity of the polymer-surface hydrogen-bonding interactions. These studies also indicate that the degree of recognition element functionalization of both the polymer and the surface is crucial in determining the rate, selectivity, and coverage of polymer on the surface.

Inhibition and acceleration of deuterium exchange in amide-functionalized monolayer-protected gold clusters.

Hydrogen/deuterium exchange rates in amide-functionalized monolayer protected gold clusters (MPCs) are controlled by the radial nature of the surface, with inhibition and catalysis observed at different chain lengths.