Enhancement of dye regeneration kinetics in dichromophoric porphyrin-carbazole triphenylamine dyes influenced by more exposed radical cation orbitals

Reduction kinetics of oxidized dyes absorbed on semiconductor surfaces and immersed in redox active electrolytes has been mainly modeled based on the free energy difference between the oxidation potential of the dye and the redox potential of the electrolyte. Only a few mechanisms have been demonstrated to enhance the kinetics by other means. In this work, the rate constant of the reduction of oxidized porphyrin dye is enhanced by attaching non-conjugated carbazole triphenylamine moiety using iodine/triiodide and tris(2,2′-bispyridinium)cobalt II/III electrolytes. These results are obtained using transient absorption spectroscopy by selectively probing the regeneration kinetics at the porphyrin radical cation and the carbazole triphenylamine radical cation absorption wavelengths. The enhancement in the reduction kinetics is not attributed to changes in the driving force, but to the more exposed dye cation radical orbitals of the dichromophoric dye. The results are important for the development of high efficiency photo-electrochemical devices with minimalized energy loss at electron transfer interfaces

Mapping of N−C bond formation from a series of crystalline peri‐substituted naphthalenes by charge density and solid‐state NMR methodologies

A combination of charge density studies and solid state nuclear magnetic resonance (NMR) 1JNC coupling measurements supported by periodic density functional theory (DFT) calculations is used to characterise the transition from an n–π* interaction to bond formation between a nucleophilic nitrogen atom and an electrophilic sp2 carbon atom in a series of crystalline peri‐substituted naphthalenes. As the N⋅⋅⋅C distance reduces there is a sharp decrease in the Laplacian derived from increasing charge density between the two groups at ca. N⋅⋅⋅C = 1.8 Å, with the periodic DFT calculations predicting, and heteronuclear spin‐echo NMR measurements confirming, the 1JNC couplings of ≈3–6 Hz for long C−N bonds (1.60–1.65 Å), and 1JNC couplings of 2.1 Å

PTF11eon/SN2011dh: Discovery of a Type IIb Supernova From a Compact Progenitor in the Nearby Galaxy M51

On May 31, 2011 UT a supernova (SN) exploded in the nearby galaxy M51 (the Whirlpool Galaxy). We discovered this event using small telescopes equipped with CCD cameras, as well as by the Palomar Transient Factory (PTF) survey, and rapidly confirmed it to be a Type II supernova. Our early light curve and spectroscopy indicates that PTF11eon resulted from the explosion of a relatively compact progenitor star as evidenced by the rapid shock-breakout cooling seen in the light curve, the relatively low temperature in early-time spectra and the prompt appearance of low-ionization spectral features. The spectra of PTF11eon are dominated by H lines out to day 10 after explosion, but initial signs of He appear to be present. Assuming that He lines continue to develop in the near future, this SN is likely a member of the cIIb (compact IIb; Chevalier and Soderberg 2010) class, with progenitor radius larger than that of SN 2008ax and smaller than the eIIb (extended IIb) SN 1993J progenitor. Our data imply that the object identified in pre-explosion Hubble Space Telescope images at the SN location is possibly a companion to the progenitor or a blended source, and not the progenitor star itself, as its radius (~10^13 cm) would be highly inconsistent with constraints from our post-explosion photometric and spectroscopic data

Modulation of donor-acceptor distance in a series of carbazole push-pull dyes; A spectroscopic and computational study

A series of eight carbazole-cyanoacrylate based donor-acceptor dyes were studied. Within the series the influence of modifying the thiophene bridge, linking donor and acceptor and a change in the nature of the acceptor, from acid to ester, was explored. In this joint experimental and computational study we have used electronic absorbance and emission spectroscopies, Raman spectroscopy and computational modeling (density functional theory). From these studies it was found that extending the bridge length allowed the lowest energy transition to be systematically red shifted by 0.12 eV, allowing for limited tuning of the absorption of dyes using this structural motif. Using the aforementioned techniques we demonstrate that this transition is charge transfer in nature. Furthermore, the extent of charge transfer between donor and acceptor decreases with increasing bridge length and the bridge plays a smaller role in electronically mixing with the acceptor as it is extended

Aldehyde isomers of porphyrin: A spectroscopic and computational study

Two diaryl porphyrin isomers have been analyzed using Raman and resonance Raman, electronic absorption,1HNMR spectroscopies coupled with density functional theory approaches. Despite similar nature, these isomers exhibit distinct experimental signatures, which in each case have be simulated by computational methods. Porphyrin saddling may explain the variations seen experimentally, where the degeneration of frontier molecular orbitals occurs. Optical interaction is observed from the aldehyde moiety with contribution to LUMO and LUMO+2 orbitals; and is confirmed by resonance Raman spectroscopy. Configuration interaction is modulated as a function of aldehyde position, resulting in 20% variation of the Q:B ratio from 0.144 to 0.114

Synthesis and Light-Induced Actuation of Photo-Labile 2-Pyridyl-1,2,3-Triazole Ru(bis-bipyridyl) Appended Ferrocene Rotors

To realise useful control over molecular motion in the future an extensive toolbox of both actionable molecules and stimuli-responsive units must be developed. Previously, our laboratory has reported 1,1′-disubstituted ferrocene (Fc) rotor units which assume a contracted/π-stacked conformation until complexation of cationic metal ions causes rotation about the Ferrocene (Fc) molecular ‘ball-bearing’. Herein, we explore the potential of using the photochemical ejection of [Ru(2,2′-bipyridyl)2]2+ units as a stimulus for the rotational contraction of new ferrocene rotor units. Fc rotors with both ‘regular’ and ‘inverse’ 2-pyridyl-1,2,3-triazole binding pockets and their corresponding [Ru(2,2′-bipyridyl)2]2+ complexes were synthesised. The rotors and complexes were characterised using nuclear magnetic resonance (NMR) and ultraviolet (UV)-visible spectroscopies, Electro-Spray Ionisation Mass Spectrometry (ESI–MS), and electrochemistry. The 1,1′-disubstituted Fc ligands were shown to π-stack both in solution and solid state. Density Functional Theory (DFT) calculations (CAM-B3LYP/6-31G(d)) support the notion that complexation to [Ru(2,2′-bipyridyl)2]2+ caused a rotation from the syn- to the anti-conformation. Upon photo-irradiation with UV light (254 nm), photo-ejection of the [Ru(2,2′-bipyridyl)2(CH3CN)2]2+ units in acetonitrile was observed. The re-complexation of the [Ru(2,2′-bipyridyl)2]2+ units could be achieved using acetone as the reaction solvent. However, the process was exceedingly slowly. Additionally, the Fc ligands slowly decomposed when exposed to UV irradiation meaning that only one extension and contraction cycle could be completed

Synthesis and Light-Harvesting Potential of Cyanovinyl β-Substituted Porphyrins and Dyads

Knoevenagel condensation has been utilized as an alternative way to synthesize a series of β-vinyl-substituted porphyrins and porphyrin dyads with good to excellent yields. The condensation of β-formyl porphyrins and phenylacetonitriles allows control of the substitution pattern and metal centres in the porphyrin dyads, allowing the use of metallated synthons. While the optical and electronic properties of the resulting porphyrin dyes are perturbed by the presence of the cyano substituent, this does not significantly affect their use. For example, Raman spectroscopy, in agreement with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, show porphyrin electronic transitions with delocalization of frontier molecular orbital electron density onto the β substituent. A comparison of the photovoltaic performance of a carboxylated cyanostyryl condensation product and the unsubstituted analogue in dye-sensitized solar cells (DSSCs) was made. Although the devices showed similar efficiency, the device containing the cyano-substituted dye showed an extended incident photon-to-current conversion efficiency (IPCE) due to a slight red-shift in absorption and an increase in photovoltage as a result of a longer electron lifetime. This minimal change in light-harvesting performance highlights the potential of this Knoevenagel synthetic methodology for producing light-harvesting porphyrin dyes

Controlled Formation of Heteroleptic [Pd₂(L_a)₂(L_b)₂]⁴⁺ Cages

Metallo­supra­molecular architectures are beginning to be exploited for a range of applications including drug delivery, catalysis, molecular recognition, and sensing. For the most part these achievements have been made with high-symmetry metallo­supra­molecular architectures composed of just one type of ligand and metal ion. Recently, considerable efforts have been made to generate metallo­supra­molecular architectures that are made up of multiple different ligands and/or metals ions in order to obtain more complex systems with new properties. Herein we show that the addition of an electron-rich 2-amino-substituted tripyridyl ligand, 2,6-bis­(pyridin-3-ylethynyl)­pyridine (<b>2A-tripy</b>), to a solution of the [Pd₂(<b>tripy</b>)₄]⁴⁺ cage resulted in the clean generation of a hetero­leptic [Pd₂(<b>tripy</b>)₂­(<b>2A-tripy</b>)₂]⁴⁺ architecture. The formation of the mixed-ligand cage [Pd₂(<b>tripy</b>)₂­(<b>2A-tripy</b>)₂]⁴⁺ was confirmed using ¹H NMR spectroscopy, diffusion-ordered spectroscopy, and rotating-frame nuclear Overhauser effect spectroscopy and high-resolution electrospray ionization mass spectrometry. Density functional theory calculations suggested the <i>cis</i> isomer was more stable that the <i>trans</i> isomer. Additionally, the calculations indicated that the hetero­leptic palladium­(II) cages are kinetically metastable intermediates rather than the thermodynamic product of the reaction. Competition experiments supported that finding and showed the cages are long-lived in solution at room temperature. Finally, it was shown that the addition of <b>2A-tripy</b> to a range of preformed [Pd₂(<b>L</b>_<b>tripy</b>)₄]⁴⁺ cages cleanly generated the mixed-ligand systems. Three other systems displaying different <i>exo</i> and <i>endo</i> functionalities within the cage assembly were generated, suggesting that this method could be applied to synthesize a range of highly functionalized hetero­leptic <i>cis</i>-[Pd₂(<b>L</b>_<b>a</b>)₂­(<b>L</b>_<b>b</b>)₂]⁴⁺ cages

Application of terpyridyl ligands to tune the optical and electrochemical properties of a conducting polymer

We present a simple and effective way of using metal and metal-ligand modifications to tune the electrochemical and optical properties of conducting polymers. To that end, a polyterthiophene functionalized with terpyridine moieties was synthesized and then the resulting film\u27s surface or bulk was modified with different metal ions, namely Fe2+, Zn2+and Cu2+and terpyridine. The modification of the terpyridine functionalized polyterthiophene film by Fe2+increased the absorptivity and electrochemical capacitance of the conducting polymer, and improved its conjugation. Further modification by Zn2+and Cu2+resulted in dramatically different spectroelectrochemical properties of the film. Moreover, the influence of the solvents (ACN and 1:1 ACN:H2O) in conjunction with the metal ion applied for the modification was found crucial for the electrochemical and optical properties of the films