Photoinduced Electron Transfer Phenomena Research Articles

Facile synthesis of yellow emissive heteroatom doped carbon quantum dots fluorescent probe with superior quantum yield for fast-track ionic detection in aqueous media

In this work, heteroatom (B and N) doped carbon quantum dots (CQDs) materials were synthesized via facile hydrothermal method using o-phenylenediamine (o-PD) as a nitrogen source and 3-aminophenyl boronic acid (3APBA) as a boron source. The synthesis parameters were optimized and optimal synthesis temperature and reaction time were 260 °C and 2 h, respectively. The chemical structures were characterized using various techniques. The experimental results showed that B,N co-doped CQDs had the strongest fluorescence intensity when the weight ratio of 3APBA:o-PD was 3:1 and showed a phenomenal quantum yield of 59% with high selectivity for Fe3+ and Hg2+ ions, with quenching constants 1.25 × 103 M–1 and 8.3 × 103 M–1, respectively. The high fluorescence quenching was attributed to the photoinduced electron transfer phenomenon, making it suitable for fluorescent sensing materials. Cytotoxicity data revealed synthesized materials are safe for biomedical applications within a 1–10 µg/mL concentration.

Multi-stimuli responsive fluorescence of amphiphilic AIEgen copolymers for ultrafast, highly sensitive and selective copper ion detection in water

Novel multi-stimuli responsive fluorescence sensors based on amphiphilic copolymers containing hydrophilic N-isopropylmethacrylamide (NIPAM) and AIEgenic tetraphenylethylene-dipicolylamine (TPEDPA) monomers attached to side-chains of copolymers are synthesized. Two copolymers poly(NIPAM)x-co-(TPEDPA)y prepared by free radical polymerization with different molar ratios of monomers NIPAM and TPEDPA (i.e., x:y = 60:1 and 175:1 for P1 and P2, respectively) show good solubilities in organic solvents and water, which exhibit strong cyan fluorescence at 466 nm in aggregation and solid states due to AIE behaviors of TPE units. Upon various external stimuli (temperatures and acid/base conditions), P1 and P2 possess excellent reversible thermo- and pH-responsive fluorescence turn-off/on cyan emissions of TPE units. In addition, with DPA receptor, P1 and P2 are applied as ultrafast, selective and sensitive fluorescence probes for copper ion detection in water based on the TPE fluorescence quenching via photoinduced electron transfer (PET) phenomena, which can be recovered by the addition of disodium ethylenediaminetetraacetate solution. Owing to good water solubilities, amphiphilic copolymers P1 and P2 (containing only 1.6 and 0.6 % molar ratios of AIEgen) exhibit significant sensing towards Cu2+ with very prominent limit of detection values (LOD = 57 and 72 nM, respectively), which are much better than that of hydrophobic monomer TPEDPA (590 nM). Moreover, the fluorescence quenching of TPE units due to PET phenomena is further confirmed by theoretical calculations. Additionally, as an excellent quenching fluorescence sensor with good biocompatibility of P1, its recognition of copper ion and bio-imaging applications in living cells are also reported in this research.

A novel chromone and rhodamine derivative as fluorescent probe for the detection of Zn(II) and Al(III) based on two different mechanisms

In this study, a novel fluorescent probe, 6‑hydroxychromone‑3‑carbaldehyde‑(rhodamine B carbonyl) hydrazine (L), for Zn2+ and Al3+ was designed and synthesized. Initially, this probe L exhibited inferior fluorescence emission peak centered at 488 nm in EtOH/HEPES solution (3/1, 10.0 μM HEPES, pH 7.4) when excited at 421 nm. After the addition of Zn2+, this probe L displayed excellent selectivity towards Zn2+ with obvious fluorescence color change from colorless to yellow, which might be attributed to the formation of a 1:1 ligand-metal complex resulting in the inhibition of photo-induced electron transfer phenomenon. Whereas, the prepared Zn2+ complex of L could be used as a ratiometric fluorescent probe to detect Al3+ on the basis of fluorescence resonance energy transfer mechanism. This ligand-metal complex of Zn2+ (LZn) showed high selectivity towards Al3+ with obvious enhancement in fluorescence emission intensity at 580 nm and remarkable decrease in fluorescence emission intensity at 488 nm, and the fluorescence color also changed from yellow to pink. Furthermore, the detection limit of the probe L, LZn towards Zn2+, Al3+ were 1.25 × 10−7 M and 3.179 × 10−6 M, respectively. Additionally, the complexation properties of L towards Zn2+ and LZn towards Al3+ were studied in detail.

Photoinduced electron transfer in layer-by-layer thin solid films containing cobalt oxide nanosheets, porphyrin, and methyl viologen.

The well-known layer-by-layer (LbL) method can be used to prepare solid thin films with a controlled electron transfer direction by appropriately stacking metal oxide nanosheets and functional organic ions. In this study, we prepared thin solid films consisting of cobalt oxide nanosheets (CoNSs) as the electron transfer medium, α,β,γ,δ-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) as the electron donor, and 1,1'-dimethyl-4,4'-bipyridinium or methyl viologen (MV) as the electron acceptor. We investigated the photoinduced electron transfer phenomenon in these films by irradiating them with 450 nm light. Irradiating the LbL thin solid films prepared with the CoNS/TMPyP/CoNS/MV/CoNS sequence under reduced pressure led to the production of a one-electron reduction compound of MV. Hence, photoinduced electron transfer from TMPyP to MV bound to CoNSs occurred in these LbL thin solid films. However, the conduction band of CoNSs, as determined by the photoabsorption spectral and photoelectrochemical measurements, was much higher than the lowest unoccupied molecular orbital level of TMPyP. Our findings indicate that the observed equipotential photoinduced electron transfer was caused by the metallic electron conductivity of CoNSs, which show a unique charge arrangement of Co3+ and Co4+. Moreover, it was also found that the observed photoinduced charge separation state has a longer life-time (>5 h) under the reduced conditions.

Discovery, understanding, and bioapplication of organic fluorophore: a case study with an indolizine-based novel fluorophore, Seoul-Fluor.

Owing to its high sensitivity and great applicability, the fluorescence phenomenon has been considered as an inevitable research tool in the modern scientific fields of chemistry, biology, materials science, biomedical science, and their interfaces. Many strategies have been pursued to understand and manipulate the photophysical properties of fluorescent materials, but the scientific community has been focused on the repeated application of existing organic fluorophores or the identification of unique fluorescence properties in a trial-and-error basis without systematic studies. Moreover, recent studies are emphasizing the necessity of deeper understanding about the structure-photophysical property relationship of organic fluorophores for the development of better fluorescent probes. Herein, we provide an overview of a novel fluorescent molecular framework, Seoul-Fluor, which can be rationally engineered to furnish a wide variety of fluorophores in terms of the photophysical properties. Seoul-Fluor is built on an indolizine-based fluorescent platform with three different positions to introduce various substituents: R(1) and R(2) substituents for electronic perturbation; R(3) substituent as a functional handle for bioconjugation. Over the past decade, we have demonstrated that the Seoul-Fluor system has (i) tunable and predictable emission wavelength covering a full visible-color range; (ii) controllable quantum yield via photoinduced electron transfer phenomenon; and (iii) environment-sensitive fluorogenic properties that can be modified through intramolecular charge transfer processes. We convincingly demonstrated the prediction of photophysical properties, that is, emission wavelength and quantum yield, through the construction of a systematic set of analogues and the subsequent analysis of their photophysical properties without the highly sophisticated theoretical support. Guided by quantifiable parameters such as the Hammett substituent constants or energy levels of the molecular orbitals, this unique organic fluorophore can serve as a versatile molecular platform for the development of novel fluorescent switchable biosensors and fluorogenic bioprobes. In this Account, we will discuss the discovery and recent progress made on Seoul-Fluor, the rational design of Seoul-Fluor-based bioprobes, and their practical applications to specific biological processes that are facilitated by systematic studies of the structure-photophysical property relationships.

Photoinduced electron transfer in aqueous carbon nanotube/block copolymer/CdS hybrids: application in the construction of photoelectrochemical cells

Pristine and shorted multi-walled carbon nanotubes (pMWCNT and sMWCNT, respectively) non-covalently modified with a block copolymer (poly[sodium (2-sulfamate-3-carboxylate) isoprene-b-styrene]—abbreviated as CSI) are used for the formation of CdS semiconductor nanohybrids. The CdS nanoparticles are preferentially localized on the surface of the nanotubes due to specific interactions with the polymer chains. In these nanohybrid materials photoinduced electron transfer phenomena are found to occur from the photoexcited CdS nanoparticles to the nanotubes as evidenced by the efficient fluorescence emission quenching of CdS nanoparticles. Nanosecond transient absorption spectroscopy sheds light on the transient species formed by charge separation, namely (pMWCNT)˙−/CSI/(CdS)˙+ and (sMWCNT)˙−/CSI/(CdS)˙+. The MWCNT/CSI/CdS nanohybrid materials are deposited onto ITO electrodes by the drop-casting method. The ITO/sMWCNT/CSI/CdS electrode exhibit an incident photon to photocurrent efficiency (IPCE) of 7% at an applied bias of +0.2 V vs.SCE in a standard three-compartment electrochemical cell. Direct electron injection from the reduced nanotubes to ITO electrode after the photoinduced charge separation is responsible for the photocurrent generation.

Electrical transport properties of fullerene peapods interacting with light

In this paper, we investigate the transport properties of field-effect transistors (FETs) based on various kindsof fullerene (C60, C70,and C84) peapods. The encapsulation of various fullerenes inside single-walled carbonnanotubes (SWNTs) is characterized by TEM and Raman spectroscopy. Ourresults indicate that the transport characteristics of p-type SWNTs are extremelysensitive to the encapsulation of various kinds of fullerene. In the absence of lightillumination, the threshold voltage of p-type SWNTs shifts towards positive values afterC60 and C70 encapsulation, and ambipolar transport characteristics are observed forC84 peapods. The photoinduced electron transfer phenomenon is observedfor fullerene peapods under light illumination. The optical response forC60 and C70 peapod FET devices is reflected in a shift of threshold voltage towardsnegative values, and a recoverable characteristic is observed when lightis off. After a long period of light illumination, in contrast to p-typeC60 and C70 peapods, an n-type transport characteristic is observed onC84 peapods.

A dendritic fullerene—porphyrin dyad

We describe the synthesis, characterization and photophysical properties of a fullerene derivative whose structure includes a Zn-porphyrin and a second generation liquid-crystalline (LC) dendrimer. The size of the fullerene and porphyrin units with respect to the size of the LC dendrimer prevents the formation of liquid-crystalline phases. However, this system gives interesting photoinduced electron transfer phenomena. Compound has been investigated by steady state and time resolved fluorescence as well as transient absorption spectroscopy in polar and apolar solvents. We demonstrate that the fluorescence of the porphyrin unit in is quenched compared to the Zn-tetraphenylporphyrin used as reference. Femto- and picosecond transient absorption permit to identify the formation of a radical ion pair while nanosecond experiments allowed the determination of the charge recombination lifetimes.

Development of exciplex chemistry: Some fundamental aspects

Abstract

Femtosecond‐Picosecond Laser Photolysis Studies on Photoinduced Electron Transfer Phenomena in Solutions

AbstractResults of our femtosecond‐picosecond laser photolysis studies on photoinduced electron transfer phenomena in solutions including exciplex dynamics and its solvent dependences, energy gap dependences of photoinduced charge separation and charge recombination of various geminate ion pairs, mechanisms of chemical reactions via exciplexes and ion pairs, dynamics of photoinduced election transfer in hydrogen bonding complexes, dynamics and mechanisms of photoinduced electron transfer in fixed distance donor acceptor dyads and photosynthetic reaction center models, and mechanisms of electron ejection from solute fluorescent state in polar solutions are summarized and discussed.

Picosecond dynamics of photoinduced electron transfer processes in poly(N-vinylcarbazole) solid film doped with electron acceptors as revealed by transient absorption spectroscopy and dichroism measurements

Combining the measurements of the picosecond transient absorption spectra and the transient dichroism sensitive to the charge shift reaction processes, photoinduced charge separation (CS), recombination (CR) and hole transfer (HT) processes in poly(N-vinylcarbazole) solid films doped with electron acceptors were investigated. It was observed that the HT process was in competition with the CR in the initial charge-separated state produced via the excitation of the ground state CT complex. The time constant for the HT from the cation state of carbazole moiety (Cz) to neighboring Czs was obtained to be ≈ 2 ns. Primary processes in these photoinduced electron transfer phenomena were discussed by comparing the present results with those in solutions.