Thitinun Karpkird

Absorption and emission spectra of ultraviolet B blocking methoxy substituted cinnamates investigated using the symmetry-adapted cluster configuration interaction method

The absorption and emission spectra of ultraviolet B (UVB) blocking cinnamate derivatives with five different substituted positions were investigated using the symmetry-adapted cluster configuration interaction (SAC-CI) method. This series included cis- and trans-isomers of ortho-, meta-, and para-monomethoxy substituted compounds and 2,4,5-(ortho-, meta-, para-) and 2,4,6-(ortho-, para-) trimethoxy substituted compounds. The ground and excited state geometries were obtained at the B3LYP/6-311G(d) and CIS/D95(d) levels of theory. All the compounds were stable as cis- and trans-isomers in the planar structure in both the S(0) and S(1) states, except the 2,4,6-trimethoxy substituted compound. The SAC-CI/D95(d) calculations reproduced the recently observed absorption and emission spectra satisfactorily. Three low-lying excited states were found to be relevant for the absorption in the UV blocking energy region. The calculated oscillator strengths of the trans-isomers were larger than the respective cis-isomers, which is in good agreement with the experimental data. In the ortho- and meta-monomethoxy compounds, the most intense peak was assigned as the transition from next highest occupied molecular orbital (next HOMO) to lowest unoccupied molecular orbital (LUMO), whereas in the para-monomethoxy compound, it was assigned to the HOMO to LUMO transition. This feature was interpreted as being from the variation of the molecular orbitals (MOs) due to the different substituted positions, and was used to explain the behavior of the excited states of the trimethoxy compounds. The emission from the local minimum in the planar structure was calculated for the cis- and trans-isomers of the five compounds. The relaxation paths which lead to the nonradiative decay were also investigated briefly. Our SAC-CI calculations provide reliable results and a useful insight into the optical properties of these molecules, and therefore, provide a useful tool for developing UVB blocking compounds with regard to the tuning of the photoabsorption.

Photostability of water-soluble inclusion complexes of UV-filters and curcumin with gamma-cyclodextrin polymer

The water-soluble inclusion complexes of curcumin, 2-ethylhexyl-4-methoxycinnamate (EHMC) and 4-tert-butyl-4′-methoxydibenzoylmethane (DBM) with gamma-cyclodextrin polymer (pyCD) were successfully prepared and characterized by 1H-NMR, IR and UV–Vis spectroscopies. The water-solubility of EHMC–pyCD, DBM–pyCD and curcumin–pyCD was dramatically increased because of the water-soluble pyCD. The mole ratio of gamma-CD in pyCD to EHMC, DBM and curcumin were carried out as 1:1. The photostability of all inclusion complexes was investigated in water and ethylene glycol and compared with free active ingredients. It was found that the photostability of EHMC–pyCD was greatly enhanced whereas those of DBM–pyCD and curcumin–pyCD in water were decreased due to the acceleration of the photodegradation reaction inside the gamma-CD cavity. These results were able to be used as a solubilizer for cosmetic and also pharmaceutical applications.

The photoinduced transformation of fluorescent DNA base analogue tC triggers DNA melting

While fluorescent analogues of the canonical nucleobases have proven to be highly valuable in a large number of applications, up until today, fluorescent DNA base analogues remain virtually inapplicable for single-molecule fluorescence experiments which require extremely bright and photostable dyes. Insight into the photodegradation processes of these fluorophores is thus a key step in the continuous development towards dyes with improved performances. Here, we show that the commercially available fluorescent nucleobase analogue tC under intense long-term illumination and in the presence of O2 is degraded to form a single photoreaction product which we suggest to be the sulfoxide form of tC. The photoproduct is characterized by a blue-shifted absorption and a less intense fluorescence compared to that of tC. Interestingly, when tC is positioned inside double-stranded DNA this photodriven conversion of tC to its photoproduct greatly reduces the duplex stability of the overall double helix in which the probe is positioned. Since tC can be excited selectively at 400 nm, well outside the absorption band of the natural DNA bases, this observation points towards the application of tC as a general light-triggered switch of DNA duplex stability.

Inclusion complexes and photostability of UV filters and curcumin with beta-cyclodextrin polymers: effect on cross-linkers

Beta-cyclodextrin polymers (pbCD) cross-linked by epichlorohydrin (pbCDE) and citric acid (pbCDC) were prepared in this work. The inclusion complexes of pbCDE and pbCDC with curcumin and two commercial UV filters, 2-ethylhexyl-p-methoxycinnamate (EHMC) and 4-tert-butyl-4′-methoxydibenzoylmethane (DBM) were investigated. The UV absorption of these three compounds observed in water indicated that the water solubility of these three hydrophobic compounds increased. The amount of EHMC was higher in both pbCDE and pbCDC than curcumin and DBM, respectively. The photostability of these three compound inclusion complexes with pbCDE and pbCDC were also studied in water and ethylene glycol. It was found that the photostability of the three compounds improved upon formation of the inclusion complex with pbCDE in an aqueous and ethylene glycol solution. The acidity of the crosslink moiety effects to the inclusion complex formation and the photostability of the guests suggesting that more acidity of citric acid decreased the formation and stability of all guest compounds.

Study of Colloidal Suspensions of Silicon Nanoparticles: Effect of Surface Oxidation on the Photoluminescence Property

Nanosilicon is currently under intensive research owing to its extremely promising properties, particularly in photonics domain. However, the photoluminescence (PL) mechanism of silicon nanocrystal remains unclear. We propose, in this paper, a simple method to investigate the PL properties of silicon nanoparticles by exposing the nanoparticles directly to the solvents. The interaction between the nanoparticles and different solvents allows us to assume that not only the quantum size effect but also the surface defect states play a critical role in the PL mechanism, especially at high energy region. This can be confirmed by the results of Transmission Electron Microscopy, FTIR and Raman Spectroscopy.

Photostability of Monoazo Disperse Dyes in Different Solvents

Twelve monoazo disperse dyes were synthesized and then characterized by melting point (m.p.) measurement, elemental analysis and 1H-NMR. The photostability of monoazo disperse dyes in solvents with different polarities was evaluated thereafter the dyes in each solvent were irradiated with visible light for 8 hours. The percentage of photostability of the dye decreased from the initial value in the range of 5-10%. The photostability was affected by the substituted group of the dyes regardless of the solvent used. Different R1 group on the diazo component increased the photostability in order of H˃CN˃Cl. The photostability of the dye was also higher when R2 group on the coupling component was a methyl group.

Dyeing and Fastness Properties of Natural Dyes on Cotton Grafted with Monochlorotriazine-β-Cyclodextrin

The main goal of this work was to study the possibility of improving the natural dye uptake and their fastness properties on cotton fabrics by the application of monochlorotriazine-β- cyclodextrin (MCT-β-CD). Hence, MCT-β-CD was synthesized, characterized, and grafted on cotton fabrics via pad and cure method. The existence of MCT-β-CD on cotton fabrics was confirmed by nitrogen content (%N). Natural dyes used were colorants extracted from turmeric and cassumunar powders, and a commercial natural dye i.e. Natural Red Brown. The commercial one was water soluble whereas the extracted dyes were sparingly soluble in water. These natural dyes were applied on cotton by pad-dry method. The extracted dyes on MCT-β-CD treated cotton fabrics gave higher visual color yield (K/S) than the untreated ones. In contrast, a commercial natural dye exhibited lower color yield on the treated fabrics because of its water soluble nature. The color fastnesses of the natural dyes on the treated cotton fabrics were improved from the untreated cotton samples.