Unraveling the Origin of Multichannel Circularly Polarized Luminescence in a Pyrene-Functionalized Topologically Chiral [2]Catenane.

Mechanically interlocked molecules (MIMs) are promising platforms for developing functionalized artificial molecular machines. The construction of chiral MIMs with appealing circularly polarized luminescence (CPL) properties has boosted their potential application in biomedicine and the optical industry. However, there is currently little knowledge about the CPL emission mechanism or the emission dynamics of these related MIMs.

Ultrafast spectroscopy study of DNA photophysics after proflavine intercalation.

Proflavine (PF), an acridine DNA intercalating agent, has been widespread applied as an anti-microbial and topical antiseptic agent due to its ability to suppress DNA replication. On the other hand, various studies show that PF intercalation to DNA can increase photogenotoxicity and has potential chances to induce carcinomas of skin appendages. However, the effects of PF intercalation on the photophysical and photochemical properties of DNA have not been sufficiently explored.

Ultrafast and Multichannel Generation of the Triplet State in DNA-Intercalated Gilvocarcin V for an Enhanced Photoaddition Reaction.

Gilvocarcin V (GV) is a natural antibiotic exhibiting excellent antitumor activities and remarkably low toxicity in near-ultraviolet or visible light-dependent treatment. Notwithstanding, the [2 + 2] cycloaddition reaction between GV and thymine has been proven to be the key for its function in photodynamic therapy, and crucial mechanistic details about such a reaction are poorly understood. In this study, the electronic relaxation pathways and photoaddition reaction are characterized by femto- to nanosecond time-resolved spectroscopy combined with quantum chemical calculation.

Tracking the Early Stage of Triplet-Induced Photodamage in a DNA Dimer and Oligomer Containing 5-Methylcytosine.

Methylation at the C5 position of cytosine, a naturally occurring epigenetic modification on DNA, shows a high correlation with mutational hotspots in disease such as skin cancer. Due to its essential biological relevance, numerous studies were devoted to confirming that the methylated sites favor the formation of the cyclobutane pyrimidine dimer (CPD), a well-known UV-induced lesion. However, photophysical and photochemical properties of dinucleotides and polynucleotides containing 5-methylcytosine (C) remain elusive.

Excited State Kinetics of Benzo[a]pyrene Is Affected by Oxygen and DNA.

Benzo[a]pyrene is a widespread environmental pollutant and a strong carcinogen. It is important to understand its bio-toxicity and degradation mechanism. Herein, we studied the excited state dynamics of benzo[a]pyrene by using time-resolved fluorescence and transient absorption spectroscopic techniques.

Distinct doorway states lead to triplet excited state generation in epigenetic RNA nucleosides.

-Hydroxymethyladenosine (hmA) and -formyladenosine (fA) are two important intermediates during the demethylation process of -methyladenosine (mA), which has been proven to show epigenetic function in mRNA. However, there is no knowledge about how the chemical integrity and stability could be altered when these two nucleosides are exposed to ultraviolet (UV) radiation. Herein, we report the first study on excited state dynamics of hmA and fA in solutions by using femtosecond time-resolved spectroscopy and quantum chemistry calculations.

Ultrafast Electron Transfer Dynamics of Organic Polymer Nanoparticles with Graphene Oxide.

We prepared organic polymer poly-3-hexylthiophene (p3ht) nanoparticles (NPs) and graphene oxide (GO)/reduced graphene oxide (RGO) composites p3ht NPs-GO/RGO by using the reprecipitation method. We demonstrated that GO/RGO could improve the ordering and planarity of p3ht chains as well as the formation of p3ht NPs, and confirmed the effects of GO/RGO on the fluorescence and carrier transport dynamics of p3ht NPs by using femtosecond fluorescence upconversion and transient absorption (TA) techniques. Ultrafast electron transfer (∼1 ps) between GO/RGO and p3ht NPs quenched the fluorescence of p3ht NPs, indicating excellent properties of p3ht NPs-GO/RGO as the charge transfer complexes.

Identification of Alkoxy Radicals as Hydrogen Atom Transfer Agents in Ce-Catalyzed C-H Functionalization.

The intermediacy of alkoxy radicals in cerium-catalyzed C-H functionalization via H-atom abstraction has been unambiguously confirmed. Catalytically relevant Ce(IV)-alkoxide complexes have been synthesized and characterized by X-ray diffraction. Operando electron paramagnetic resonance and transient absorption spectroscopy experiments on isolated pentachloro Ce(IV) alkoxides identified alkoxy radicals as the sole heteroatom-centered radical species generated via ligand-to-metal charge transfer (LMCT) excitation.

Excited-State Dynamics of Proflavine after Intercalation into DNA Duplex.

Proflavine is an acridine derivative which was discovered as one of the earliest antibacterial agents, and it has been proven to have potential application to fields such as chemotherapy, photobiology and solar-energy conversion. In particular, it is well known that proflavine can bind to DNA with different modes, and this may open addition photochemical-reaction channels in DNA. Herein, the excited-state dynamics of proflavine after intercalation into DNA duplex is studied using femtosecond time-resolved spectroscopy, and compared with that in solution.

Constructing Chromium Multioxide Hole-Selective Heterojunction for High-Performance Perovskite Solar Cells.

Perovskite solar cells (PSCs) suffer from significant nonradiative recombination at perovskite/charge transport layer heterojunction, seriously limiting their power conversion efficiencies. Herein, solution-processed chromium multioxide (CrO ) is judiciously selected to construct a MAPbI /CrO /Spiro-OMeTAD hole-selective heterojunction. It is demonstrated that the inserted CrO not only effectively reduces defect sites via redox shuttle at perovskite contact, but also decreases valence band maximum (VBM)-HOMO offset between perovskite and Spiro-OMeTAD.

Ribose and Deoxyribose Group Alter Excited-State Dynamics of 5-Azacytosine in Solution.

5-Azacytosine (5-AC) is one of the best interesting noncanonical nucleobases due to its functionalization and structural imitation of natural bases. 5-AC can be used as the scaffold of two important chemotherapeutic medicines, 5-azacytidine and 2'-deoxy-5-azacytidine. Furthermore, increased sensitivity to UV leads to the photochemical effects of 5-AC also attracted attention.

Ultrafast Förster resonance energy transfer between tyrosine and tryptophan: potential contributions to protein-water dynamics measurements.

Ultrafast Förster Resonance Energy Transfer (FRET) between Tyrosine (Tyr, Y) and Tryptophan (Trp, W) in the model peptides Trp-(Pro)-Tyr (WPY) has been investigated using a femtosecond up-conversion spectrophotofluorometer. The ultrafast energy transfer process (<100 ps) in short peptides (WY, WPY and WP2Y) has been resolved. In fact, this FRET rate is found to be mixed with the rates of solvent relaxation (SR), ultrafast population decay (QSSQ) and other lifetime components.

A fraction of NADH in solution is "dark": Implications for metabolic sensing via fluorescence lifetime.

The metabolic cofactor and energy carrier NADH (nicotinamide adenine dinucleotide, reduced) has fluorescence yield and lifetime that depends strongly on conformation, a fact that has enabled metabolic monitoring of cells via FLIM (Fluorescence Lifetime Microscopy). Using femtosecond fluorescence upconversion, we show that this molecule in solution participates in ultrafast self-quenching along with both bulk solvent relaxation and spectral relaxation on 1.4 and 26 ps timescales.

pH Controlled Intersystem Crossing and Singlet Oxygen Generation of 8-Azaadenine in Aqueous Solution.

Azabases are intriguing DNA and RNA analogues and have been used as effective antiviral and anticancer medicines. However, photosensitivity of these drugs has also been reported. Here, pH-controlled intersystem crossing (ISC) process of 9H 8-azaadenine (8-AA) in aqueous solution is reported.

Molecular Origin of Ultrafast Water-Protein Coupled Interactions.

The fluctuations of hydration water and the protein are coupled together at the protein surface and often such water-protein dynamic interactions are controlled presumably by hydration water motions. However, direct evidence is scarce and it requires measuring the dynamics of hydration water and protein side chain simultaneously. Here, we use a unique protein with a single tryptophan to directly probe interfacial water and related side chain relaxations with temperature dependence.

Time-Resolved Fluorescence of Water-Soluble Pyridinium Salt: Sensitive Detection of the Conformational Changes of Bovine Serum Albumin.

In this paper, we report a pyridinium salt "turn-on" fluorescent probe, 4-[2-(4-Dimethylamino-phenyl)-vinyl]-1-methylpyridinium iodide (p-DASPMI), and applied its time-resolved fluorescence (TRF) to monitor the protein conformational changes. Both the fluorescence lifetime and quantum yield (QY) of p-DASPMI were increased about two orders of magnitude after binding to the protein bovine serum albumin (BSA). The free p-DASPMI in solution presents an ultrashort fluorescence lifetime (12.

Using Pyridinium Styryl Dyes as the Standards of Time-Resolved Instrument Response.

In this paper, two pyridinium styryl dyes, [2-(4-dimethylamino-phenyl)-vinyl]-1-methylpyridinium iodide (DASPMI), were synthesized and characterized by steady state fluorescence spectroscopy as well as picosecond and femtosecond time-resolved fluorescence spectroscopies. Both dyes exhibit large Stokes shifts and fluorescence decays equivalent to the instrument response function (IRF) standards employed in time-correlated single-photon counting. Due to their styryl and pyridinium moieties, DASPMIs have higher peak fluorescence intensity and shorter excited-state lifetimes than iodide ion-quenched fluorophores.

Determination of Protein Surface Hydration by Systematic Charge Mutations.

Protein surface hydration is critical to its structural stability, flexibility, dynamics, and function. Recent observations of surface solvation on picosecond time scales have evoked debate on the origin of such relatively slow motions, from hydration water or protein charged side chains, especially with molecular dynamics simulations. Here we used a unique nuclease with a single tryptophan as a local probe and systematically mutated three neighboring charged residues to differentiate the contributions from hydration water and charged side chains.

Fluorescence kinetics of Trp-Trp dipeptide and its derivatives in water via ultrafast fluorescence spectroscopy.

Ultrafast fluorescence dynamics of Tryptophan-Tryptophan (Trp-Trp/Trp2) dipeptide and its derivatives in water have been investigated using a picosecond resolved time correlated single photon counting (TCSPC) apparatus together with a femtosecond resolved upconversion spectrophotofluorometer. The fluorescence decay profiles at multiple wavelengths were fitted by a global analysis technique. Nanosecond fluorescence kinetics of Trp2, N-tert-butyl carbonyl oxygen-N'-aldehyde group-l-tryptophan-l-tryptophan (NBTrp2), l-tryptophan-l-tryptophan methyl ester (Trp2Me), and N-acetyl-l-tryptophan-l-tryptophan methyl ester (NATrp2Me) exhibit multi-exponential decays with the average lifetimes of 1.

Instrument response standard in time-resolved fluorescence spectroscopy at visible wavelength: quenched fluorescein sodium.

Time-resolved fluorescence properties of quenched fluorescein sodium, including self-quenching and collisional quenching by iodide, have been studied by using a picosecond time-correlated single-photon counting (TCSPC) apparatus, together with an upconversion spectrophotofluorometer with a time resolution better than 300 fs. The steady-state fluorescence intensity of fluorescein sodium reached the maximum when its concentration was 510 μM with pH > 9. Both the fluorescence intensity and lifetime decreased with increasing concentrations of NaI quencher.

Hypoxia-sensitive bis(2-(2'-benzothienyl)pyridinato-N,C(3'))iridium[poly(n-butyl cyanoacrylate]/chitosan nanoparticles and their phosphorescence tumor imaging in vitro and in vivo.

A new hypoxia-sensitive coordination compound, bis(2-(2'-benzothienyl)pyridinato-N,C(3'))iridium[poly(n-butyl cyanoacrylate)], hereafter denoted as (btp)2Ir(PBCA), is synthesized and characterized by (13)C nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). (btp)2Ir(PBCA)/chitosan [(btp)2Ir(PBCA)/CS] nanoparticles (NPs) with a core-shell structure are prepared by a two-step fabrication process. The size distributions of these NPs are measured with a Malvern size analyzer, and their morphology is observed by transmission electron microscopy (TEM).