There are numerous reports of coumarin ester derivatives, in particular phosphate esters, as photocleavable cages in biological systems. Despite the comprehensive analysis of the photocleavage mechanism, studies of 4-methylcoumarin caged phosphates and/or nucleotides were always performed at constant pH. In this work. we present the study of the pH effect on the photochemistry of (7-diethylaminocoumarin-4-yl)methyl phosphate (DEACM-P). Fluorescence and photocleavage quantum yields, as well as the fluorescence decay times were measured as a function of the pH. It was found that the pH produces significant changes in the overall photochemical quantum yield of DEACM-P, and the observed changes are complementary to those obtained from the fluorescence quantum yield. Deprotonation of DEACM-HPO(4)(-) to yield DEACM -PO(4)(2-), produces a decrease in the photochemical quantum yield (from 0.0045 to 0.0003) and an increase in the fluorescence quantum yield (from 0.072 to 0.092). Moreover, from the analysis of the decay times, we have also found that hydroxyl ion is not only relevant, but it is mechanistically involved in the photoreaction of DEACM-HPO(4)(-).

A systematic study of the electrochromic (EC) behavior of electropolymerized poly[M(salen)] films (M = Ni, Cu, and Pd) was performed by spectroelectrochemistry. Color contrast between oxidized and reduced states, stability under square wave potential cycling, coloration efficiency, and switching rate were evaluated. Five polymers were selected to assemble solid-state EC cells in a symmetrical configuration (electrode/poly[M(salen)] film/opaque electrolyte/poly[M(salen)] film/electrode). The best EC performance was found for poly[Pd(3-Mesalen)], poly[1], with 38% of initial diffuse reflectance variation and loss of 50% after 6769 cycles. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3457474] All rights reserved.

Flexible, transparent and self-supporting electrolyte films based on poly(trimethylene carbonate)/poly(ethylene oxide) (p(TMC/PEO) interpenetrating networks doped with LiClO(4) were prepared by the solvent casting technique. These novel solid polymer electrolyte (SPE) systems were characterized by measurements of conductivity, cyclic voltammetry, differential scanning calorimetry and thermogravimetry. The incorporation of solid electrolytes as components of electrochromic devices can offer certain operational advantages in real-world applications. In this study, all-solid-state electrochromic cells were characterized, using Prussian blue (PB) and poly-(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT) as complementary electrochromic compounds on poly(ethyleneterphthalate) (PET) coated with indium tin oxide (ITO) as flexible electrodes. Assembled devices with PET/ITO/PB/SPE/PEDOT/ITO/PET "sandwich-like" structure were assembled and successfully cycled between light and dark blue, corresponding to the additive optical transitions for PB and PEDOT electrochromic layers. The cells required long cycle times (>600 s) to reach full color switch and have modest stability towards prolonged cycling tests. The use of short duration cycling permitted the observation of changes in the coloration-bleaching performance in cells with different electrolyte compositions. (C) 2009 Elsevier Ltd. All rights reserved.

We recently reported on the use of caged nucleotides to attain full control of enzymatic polymerization of RNA solely by light. In the absence of light no RNA formation was possible due to the efficient caging by the coumarin moiety: after irradiation, caged ATP was released with quantitative precision and RNA polymerization was resumed. As photolabile protecting group [7-(diethylamino)coumarin-4-yl]methyl] (DEACM) was used due to its high absorbance in the visible region of the spectrum, fast deprotection kinetics and absence of radical intermediates. However, the 7-diethylamino-4-hydroxymethylcoumarin photo-product (DEACM-OH) was shown to inhibit the transcription reaction for concentrations higher than 30 mu M [5]. This inhibition has been associated with poor water solubility, which is commonly dealt with via cumbersome chemical modifications of the protecting moiety. To overcome inhibition, we evaluated the use of molecular scavengers to sequester DEACM-OH formed after irradiation. Determination of association constants of coumarin with beta-cyclodextrins allowed the assessment of its capability to remove free coumarin molecules from solution. The influence of beta-cyclodextrin in transcription reaction was also assessed. Results show that beta-cyclodextrin can be successfully used as scavenger as it increases the DEACM-OH threshold concentration for inhibition, amplifying the efficiency of light controlled in vitro transcription. (C) 2010 Elsevier B.V. All rights reserved.

Flavylium salts contain the basic structure and show a pH-dependent sequence of reactions identical to natural anthocyanins, which are responsible for most of the red and blue colors of flowers and fruits. In this work we investigated the effect of the water-soluble molecular clips C1 and C2 substituted by hydrogen phosphate or sulfate groups on the stability and reactions of the flavylium salts 1-4 by the use of UV-vis absorption, fluorescence, and NMR spectroscopy as well as of the time-resolved pH jump and flash photolysis methods. Clip C1 forms highly stable host-guest complexes with the flavylium salts 1 and 2 and the quinoidal base 3A in methanol. The binding constants were determined by fluorometric titration to be log K = 4.1, 4.7, and 5.6, respectively. Large complexation-induced (1)H NMR shifts of guest signals, Delta delta(max), indicate that in the case of the flavylium salts 1 and 2 the pyrylium ring and in the case of the quinoidal base 3A the o-hydroxyquinone ring are preferentially bound inside the clip cavity. Due to the poor solubility of these host-guest complexes in water, the association constants could be only determined in highly diluted aqueous solution by UV-vis titration experiments for the complex formation of clip C1 with the flavylium salt 3AH(+) at pH = 2 and the quinoidal base 3A at pH = 5.3 to be log K = 4.9 for both complexes. Similar results were obtained for the formation of the complexes of the sulfate-substituted clip C2 with flavylium salt 4AH(+) and its quinoidal base 4A which are slightly better soluble in water (log K = 4.3 and 4.0, respectively). According to the kinetic analysis (performed by using the methods mentioned above) the thermally induced trans-cis chalcone isomerization (4Ct -> 4Cc) and the H(2)O addition to flavylium cation 4AH(+) followed by H(+) elimination leading to hemiketal 4B are both retarded in the presence of clip C2, whereas the photochemically induced trans-cis isomerization (4Ct -> 4Cc) is not affected by clip C2. The results presented here are explained with dominating hydrophobic interactions between the molecular clips and the flavylium guest molecules. The other potential interactions (ion-ion, cation-pi, pi-pi, and CH-pi), which certainly determine the structures of these host-guest complexes to a large extent, seem to be of minor importance for their stability.