Using 7-hydroxy-1-indanone as a prototype (I), which exhibits excited-state intramolecular proton transfer (ESIPT), chemical modification has been performed at C(2)-C(3) positions by fusing benzene (molecule II) and naphthalene rings, (molecule III). I undergoes an ultrafast rate of ESIPT, resulting in a unique tautomer emission (λ(max) ∼530 nm), whereas excited-state equilibrium is established for both II and III, as supported by the dual emission and the associated relaxation dynamics. The forward ESIPT (normal to proton-transfer tautomer species) rates for II and III are deduced to be (30 ps)(-1) and (22 ps)(-1), respectively, while the backward ESIPT rates are (11 ps)(-1) and (48 ps)(-1). The ESIPT equilibrium constants are thus calculated to be 0.37 and 2.2 for II and III, respectively, giving a corresponding free energy change of 0.59 and -0.47 kcal/mol between normal and tautomer species. For III, normal and tautomer emissions in solid are maximized at 435 and 580 nm, respectively, achieving a white light generation with Commission Internationale de l'Eclairage (CIE) (0.30, 0.27). An organic light-emitting diode based on III is also successfully fabricated with maximum brightness of 665 cd m(-2) at 20 V (885 mA cm(-2)) and the CIE coordinates of (0.26, 0.35). The results provide the proof of concept that the white light generation can be achieved in a single ESIPT system.
Scientists have made tremendous efforts to gain understanding of the water molecules in proteins via indirect measurements such as molecular dynamic simulation and/or probing the polarity of the local environment. Here we present a tryptophan analogue that exhibits remarkable water catalysed proton-transfer properties. The resulting multiple emissions provide unique fingerprints that can be exploited for direct sensing of a site-specific water environment in a protein without disrupting its native structure. Replacing tryptophan with the newly developed tryptophan analogue we sense different water environments surrounding the five tryptophans in human thromboxane A 2 synthase. This development may lead to future research to probe how water molecules affect the folding, structures and activities of proteins.
Dicarboxyterpyridine chelates with π-conjugated pendant groups attached at the 5- or 6-position of the terminal pyridyl unit were synthesized. Together with 2,6-bis(5-pyrazolyl)pyridine, these were used successfully to prepare a series of novel heteroleptic, bis-tridentate Ru(II) sensitizers, denoted as TF-11-14. These dyes show excellent performance in dye-sensitized solar cells (DSCs) under AM1.5G simulated sunlight at a light intensity of 100 mW cm(-2) in comparison with a reference device containing [Ru(Htctpy)(NCS)(3)][TBA](3) (N749), where H(3)tctpy and TBA are 4,4',4"-tricarboxy-2,2':6',2"-terpyridine and tetra-n-butylammonium cation, respectively. In particular, the sensitizer TF-12 gave a short-circuit photocurrent of 19.0 mA cm(-2), an open-circuit voltage (V(OC)) of 0.71 V, and a fill factor of 0.68, affording an overall conversion efficiency of 9.21%. The increased conjugation conferred to the TF dyes by the addition of the π-conjugated pendant groups increases both their light-harvesting and photovoltaic energy conversion capability in comparison with N749. Detailed recombination processes in these devices were probed by various spectroscopic and dynamics measurements, and a clear correlation between the device V(OC) and the cell electron lifetime was established. In agreement with several other recent studies, the results demonstrate that high efficiencies can also be achieved with Ru(II) sensitizers that do not contain thiocyanate ancillaries. This bis-tridentate, dual-carboxy anchor configuration thus serves as a prototype for future omnibearing design of highly efficient Ru(II) sensitizers suited for use in DSCs.
We have designed and synthesized a series of Au(I) complexes bearing either an alkynyl−(phenylene) n −diphosphine (A-0−A-3) or a (phenylene) n −diphosphine (B-1−B-5) bridge, among which the effective distance between Au(I) and the center of the emitting ππ* chromophore can be fine-tuned via the insertion of various numbers of phenylene spacers. We then demonstrated for the first time in a systematic manner the decrease of rate constant for S 1 → T 1 intersystem crossing (ISC) k isc as the increase of the effective distance. The results also unambiguously showed that the phosphorescence could be harvested via higher S 0 → S n (n > 1) electronic excitation, followed by fast S n → T m ISC and then the population at T 1 state, bypassing the relatively slow S 1 → T 1 ISC. The results unify a recent report on higher excited-state relaxation dynamics for the late transition metal complexes (J. Am. Chem. Soc. 2012, 134, 7715−7724). The dual, far separated fluorescence and phosphorescence of the titled complexes make feasible the white light generation in a single molecule unit, as successfully demonstrated using complex B-3 as a dopant to fabricate organic light emitting diodes.
The light absorber or sensitizer is one of the most important components of dye-sensitized solar cells (DSCs). Adequate engineering of this material allows DSCs to achieve a fine balance among higher solar energy-to-electricity conversion efficiency, lower manufacturing costs, and better long-term stability. The most efficient DSCs to date are fabricated with transition metal based sensitizers. [1] For example, Grätzel and co-workers recently demonstrated that a Zn II porphyrin with donor-acceptor substituent shows a remarkable power conversion efficiency of h % 13 % under illumination with standard AM 1.5G simulated sunlight. [2] Furthermore, many Ru II sensitizers were also known to attain efficiencies greater than 10 %, [3] long before the discovery of the above Zn II dye. Besides these successes, a few quaterpyridine Ru II sensitizers showed notable absorption in the far-red to near-infrared (NIR) region, [4] with the potential to harvest lower energy protons needed for higher current density.With a view to harvesting lower energy photons, Os IIbased sensitizers seem to be an excellent option for expanding the spectral response well into the NIR region. [5] First, Os II polypyridine complexes tend to show lower energy metal-toligand charge-transfer (MLCT) transition, as a consequence of the lower oxidation potential compared to their Ru II counterparts. [6] In addition, larger spin-orbit coupling for the heavier Os II cation, in theory, induces nontrivial absorption of the 3 MLCT states extended to even lower energy. Thus, appropriately designed Os II sensitizers should display a much broader absorption profile and faster electron injection from both nonthermalized 1 MLCT and thermalized 3 MLCT excited states. [7] We expect that such a photophysical property should be important to both the DSC community and groups whose interests are in developing sensitizers for water splitting with dye-sensitized oxide semiconductors. [8] In this study, the design of Os II sensitizers conceptually takes advantage of our previously reported Ru II sensitizer TF-1, which contains 4,4',4''-tricarboxy-2,2':6,2''-terpyridine (H 3 tctpy) and dianionic 2,6-bis(1,2-pyrazol-5-yl)pyridine chelating ligands (Scheme 1). [9] This Ru II -based sensitizer showed panchromatic absorption extending to 830 nm and an oxidation potential of 0.94 V versus the normal hydrogen electrode (NHE) that ensures efficient regeneration of the oxidized sensitizers. However, if the identical architecture were adopted, the oxidation potential of the corresponding Os II sensitizer is predicted to be much less positive. [6,10] This hurdle can be circumvented by replacing pyrazolate with triazolate with aim of decreasing the electron density at the central Os II ion. This hypothesis is supported by the prior preparation of a relevant triazolate-based Ru II sensitizer, namely, TF-5 (see Scheme 1). The oxidation potential of TF-5 is shifted to 1.19 V (vs. NHE), which is 0.25 V higher in energy than that of TF-1.Encouraged by this preliminary result, we focused ...
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