Intramolecular Photo-Oxidation as a Potential Source to Probe Biological Electron Damage: A Carboxylated Adenosine Analogue as Case Study

A carboxylated adenosine analog (C-Ado−) has been synthesized and probed via time-resolved photoelectron spectroscopy in order to induce intra-molecular charge transfer from the carboxylic acid moiety to the nucleobase. Intra-molecular charge transfer can be exploited as starting point to probe low-energy electron (LEE) damage in DNA and its derivatives. Time-dependent density functional theory (TD-DFT) calculations at the B3LYP-6311G level of theory have been performed to verify that the highest occupied molecular orbital (HOMO) was located on carboxylic acid and that the lowest occupied molecular orbital (LUMO) was on the nucleobase. Hence, the carboxylic acid could work as electron source, whilst the nucleobase could serve the purpose of electron acceptor. The dynamics following excitation at 4.66 eV (266 nm) were probed using time-resolved photoelectron spectroscopy using probes at 1.55 eV (800 nm) and 3.10 eV (400 nm). The data show rapid decay of the excited state population and, based on the similarity of the overall dynamics to deoxy-adenosine monophosphate (dAMP–), it appears that the dominant decay mechanism is internal conversion following 1ππ* excitation of the nucleobase, rather than charge-transfer from the carboxylic acid to the nucleobase.

A Chromone Based Fluorescent Probe for the Effective Detection of Aluminium Ion

A new chromone moiety fused with phenyl hydrazine carboxamide as a binding site for metal ion was designed and synthesized as a colorimetric/fluorimetric probe for selective sensing of Al3+ ion. The absorption and fluorescence spectral results showed selective and sensitive recognition of Al3+ with no significant interference from other competitive metal ions. The addition of Al3+ to R brought a prompt color change from colorless to yellow and the turn-on fluorescence response with Al3+ among different cations was studied. The visible color change and turn-on fluorescence Al3+ ion with R was attributed to the intra molecular charge transfer transition. The plausible binding nature of the receptor with Al3+ has also been anticipated by the results of 1H NMR and mass spectral analysis. For the practical effectiveness, test strip prepared using probe R was successfully applied to monitor the presence of Al3+ ion in aqueous medium.

Colorless Semi-Alicyclic Copolyimides with High Thermal Stability and Solubility

A series of colorless copolyimide films with high thermal stability and good solubility are synthesized from (trifluoromethyl)biphenyl-4,4’-diamine (TFMB) with different 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) to 2,2-bis(3,4-dicarboxyphenyl)-hexafluoropropane (6FDA) dianhydride mole ratios through one-pot solution polycondensation. These copolyimide films exhibit excellent optical transparency (T400 > 90% and λ0 ~305–333 nm) with a thickness of 15 μm and good solubility in most organic solvents. The excellent optical properties are mainly attributed to the low inter- and intra-molecular charge transfer interactions due to the alicyclic structure and the strong electronegative CF3 groups. The glass transition temperature increases from 332 to 352 °C with increasing HPMDA content in the copolymers, while the thermal decomposition temperature is improved with increasing 6FDA content. These results indicate that the copolyimide films can be successfully utilized in the development of novel heat-resistant plastic substrates for the optoelectronic engineering applications.

Anthracene Based AIE Active Probe for Colorimetric and Fluorimetric Detection of Cu2+ Ions

A novel aggregation induced emission (AIE) active anthracene based dihydroquinazolinone derivative (probe 1) has been synthesized and characterized by means of spectroscopic methods. The photophysical properties of this probe have been investigated in solvents of different polarity display that fluorescence states are of intramolecular charge transfer (ICT) character. Probe 1 show clear AIE behavior in water/THF mixture on reaching water fraction 95%. The AIE behavior of probe 1 have been exploited for the detection of metal ions in aqueous solution which reveals high selectivity and sensitivity towards Cu2+ ions by colorimetrically and function as a chemosensor in a remarkable turn-off fluorescence manner. Further, the experimental results were investigated by computational means by optimizing the ground state geometries of probe 1 and probe 1-Cu complex using density functional theory (DFT) at B3LYP/6-31G∗∗ and B3LYP/6-31G∗∗(LANL2DZ) levels of theory. Intra-molecular charge transfer was observed in probe 1 while ligand to metal charge transfer (LMCT) for probe 1-Cu complex.

Improving the electroluminescence performance of blue light-emitting poly(fluorene-co-dibenzothiophene-S,S-dioxide) by tuning the intra-molecular charge transfer effects and temperature-induced orientation of the emissive layer structure

A luminous efficiency of 7.30 cd A−1was achieved in PFSO10TA2 as a result of temperature-induced orientation.

Theoretical study on photo-induced processes of 1-methyl-3-(N-(1,8-naphthalimidyl)ethyl)imidazolium halide species: an application of constrained density functional theory

Inter-molecular charge transfer (SET) and intra-molecular charge transfer (SM1) excited states are involved in the photo-induced processes of 1-methyl-3-(N-(1,8-naphthalimidyl)ethyl)imidazolium halide.

Strategies to enhance the excitation energy-transfer efficiency in a light-harvesting system using the intra-molecular charge transfer character of carotenoids

Fucoxanthin is a carotenoid that is mainly found in light-harvesting complexes from brown algae and diatoms. Due to the presence of a carbonyl group attached to polyene chains in polar environments, excitation produces an excited intra-molecular charge transfer. This intra-molecular charge transfer state plays a key role in the highly efficient (∼95%) energy-transfer from fucoxanthin to chlorophyllain the light-harvesting complexes from brown algae. In purple bacterial light-harvesting systems the efficiency of excitation energy-transfer from carotenoids to bacteriochlorophylls depends on the extent of conjugation of the carotenoids. In this study we were successful, for the first time, in incorporating fucoxanthin into a light-harvesting complex 1 from the purple photosynthetic bacterium,Rhodospirillum rubrumG9+ (a carotenoidless strain). Femtosecond pump-probe spectroscopy was applied to this reconstituted light-harvesting complex in order to determine the efficiency of excitation energy-transfer from fucoxanthin to bacteriochlorophyllawhen they are bound to the light-harvesting 1 apo-proteins.