Fluorescence Emission Efficiency Research Articles

Unusual, Highly Efficient Fluorescence Emission Enhancement of Conjugated Polymers with an Intramolecular Stack Structure through Thermal Annealing at High Temperature

Unusual, Highly Efficient Fluorescence Emission Enhancement of Conjugated Polymers with an Intramolecular Stack Structure through Thermal Annealing at High Temperature

Antibacterial Narrow‐Band‐Gap Conjugated Oligoelectrolytes with High Photothermal Conversion Efficiency

AbstractTwo conjugated oligoelectrolytes (COEs), WMG1 and WMG2, were designed with the goal of achieving near infrared absorption and high photothermal conversion efficiency. Specifically, electron‐rich thiophene and electron‐poor benzo[1,2‐c:4,5‐c′]bis[1,2,5]thiadiazole subunits were introduced into the conjugated core to modulate the optical gap and to reduce the fluorescence emission efficiency. WMG1 and WMG2 show absorption maxima at around 800 nm, which favors tissue penetration. Although relatively small in size, WMG1 and WMG2 exhibit photothermal conversion efficiencies of circa 60 % and 54 %, respectively. WMG1 shows dark toxicity to the Gram positive bacterium B. subtilis and good photothermal killing efficiency toward both B. subtilis and Gram negative E. coli, features that demonstrate the promising potential of the COE molecular design for photothermal applications.

Antibacterial Narrow-Band-Gap Conjugated Oligoelectrolytes with High Photothermal Conversion Efficiency.

Two conjugated oligoelectrolytes (COEs), WMG1 and WMG2, were designed with the goal of achieving near infrared absorption and high photothermal conversion efficiency. Specifically, electron-rich thiophene and electron-poor benzo[1,2-c:4,5-c']bis[1,2,5]thiadiazole subunits were introduced into the conjugated core to modulate the optical gap and to reduce the fluorescence emission efficiency. WMG1 and WMG2 show absorption maxima at around 800 nm, which favors tissue penetration. Although relatively small in size, WMG1 and WMG2 exhibit photothermal conversion efficiencies of circa 60 % and 54 %, respectively. WMG1 shows dark toxicity to the Gram positive bacterium B. subtilis and good photothermal killing efficiency toward both B. subtilis and Gram negative E. coli, features that demonstrate the promising potential of the COE molecular design for photothermal applications.

New pyrrolo[3,2-b]pyrrole derivatives with multiple-acceptor substitution: Efficient fluorescent emission and near-infrared two-photon absorption

Two new D-π-A organic chromophores, 1,2,4,5-tetra(4-cyanophenyl)pyrrolo[3,2-b]pyrrole (4CNPP) and 1,2,3,4,5,6-hexa(4-cyanophenyl)pyrrolo[3,2-b]pyrrole (6CNPP), were developed by modifying the electron-rich pyrrolo[3,2-b]pyrrole (PP) unit with four and six 4-cyanophenyls respectively. The compounds exhibited bright blue emissions in low- to high-polarity solvents, with high Фfs of 88–90% in toluene, as well as impressive two-photon absorption cross-sections at the near-infrared (NIR) 700 nm.

Broadband enhancement of photoluminance from colloidal metal halide perovskite nanocrystals on plasmonic nanostructured surfaces

Metal halide perovskite nanocrystals (NCs) as a new kind of promising optoelectronic material have attracted wide attention due to their high photoluminescence (PL) quantum yield, narrow emission linewidth and wideband color tunability. Since the PL intensity always has a direct influence on the performance of optoelectronic devices, it is of vital importance to improve the perovskite NCs’ fluorescence emission efficiency. Here, we synthesize three inorganic perovskite NCs and experimentally demonstrate a broadband fluorescence enhancement of perovskite NCs by exploiting plasmonic nanostructured surface consisting of nanogrooves array. The strong near-field optical localization associated with surface plasmon polariton-coupled emission effect generated by the nanogrooves array can significantly boost the absorption of perovskite NCs and tailor the fluorescence emissions. As a result, the PL intensities of perovskite NCs are broadband enhanced with a maximum factor higher than 8-fold achieved in experimental demonstration. Moreover, the high efficiency PL of perovskite NCs embedded in the polymer matrix layer on the top of plasmonic nanostructured surface can be maintained for more than three weeks. These results imply that plasmonic nanostructured surface is a good candidate to stably broadband enhance the PL intensity of perovskite NCs and further promote their potentials in the application of visible-light-emitting devices.

Versatility of Terpyridine‐Functionalised Aryl Tetrazoles: Photophysical Properties, Ratiometric Sensing of Zinc Cations and Sensitisation of Lanthanide Luminescence

Four new tetrazole‐containing species, in conjugation with terpyridine moieties through phenyl or pyridyl linkers, have been synthesised and characterised. In the series, the tetrazole functional groups are either in their acidic form or are alkylated at the N2 position with a methyl group. The photophysical properties of the species reveal moderate UV or efficient blue fluorescent emission, with photoluminescence quantum yields of around 30 % and 80 % for UV and blue emission, respectively. The spectral profiles can be reversibly modulated through protonation/deprotonation, with changes being consistent with an increase of the electron density on the tetrazole rings upon deprotonation or a decrease of the electron density on the terpyridines through protonation. The tetrazole‐containing species were also investigated for fluorescence sensing of biologically and environmentally important metal ions, highlighting a ratiometric response to the presence of Zn2+. Furthermore, this ratiometric response could be well discriminated from that of interfering Cd2+ ions. Lastly, the species have been investigated as ligands for Eu3+ and Yb3+ cations, revealing efficient sensitisation, to give typical red and near‐infrared emissions, respectively.

Enhanced Fluorescence Emission and Singlet Oxygen Generation of Photosensitizers Embedded in Injectable Hydrogels for Imaging-Guided Photodynamic Cancer Therapy.

Benefiting from their inherent localized and controlled release properties, hydrogels are ideal delivery systems for therapeutic drugs or nanoparticles. In particular, applications of hydrogels for the delivery and release of photoresponsive drugs or nanoparticles are receiving increasing attention. However, the effect of the hydrogel matrix on the fluorescence emission and singlet oxygen generation efficiency of the embedded photosensitizers (PSs) has not been clarified. Herein, meso-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) as a water-soluble PS was encapsulated into an injectable hydrogel formed by glycol chitosan and dibenzaldehyde-terminated telechelic poly(ethylene glycol). Compared to free TMPyP solution, the TMPyP encapsulated in the hydrogel exhibits three distinct advantages: (1) more singlet oxygen was generated under the same laser irradiation condition; (2) much longer tumor retention was observed due to the low fluidity of the hydrogel; and (3) the fluorescence intensity of TMPyP was significantly enhanced in the hydrogel due to its decreased self-quenching effect. These excellent characteristics lead to remarkable anticancer efficacy and superior fluorescence emission property of the TMPyP-hydrogel system, promoting the development of imaging-guided photodynamic therapy.

Photophysical and Photochemical Properties of Polyurethane Coumarin Studied by Means of Electronic Spectra

The spectroscopic and photochemical properties of polyurethane coumarine (PUC) in dimethyl sulf-oxide (DMSO), thetra hydro furan (THF), dimethyl formamide (DMF) and film state were investigated at room temperature under one photon excitation. Photodimer products were formed via UV irradiation. Syn head-to-head and syn head-to-tail photodimers were formed under one-photon (broadband UV) irradiation in polar solvents. The spectral investigation of the photochemical products of PUC revealed efficient fluorescence emission in the spectral region 300�400 nm, attributed to the syn-head-to-tail dimers of PUC. The results show that under irradiation of l ] 310 nm photodimerization process are increased and under UV irradiation with l [ 260 nm, photocleavage degree have been evidenced, too. Fluorescence spectra analysis of PUC in polar and film-based solvents reveals another very important result. The 375nm fluorescence wavelength of the PUC (exciting beam 310 nm) is about 30 times more intense than the same maximum in THF and in DMF. This result indicates a new method to confirm that PUC film photodimerisation occurs especially at its surface.

Photochemistry and Photophysics of Enediyne-Cored Polyphenylene Dendrimers

Abstract Two kinds of enediyne-cored polyphenylene dendrimer (mGn, pGn) were prepared as pure cis and trans isomers. In comparison to parent enediyne with no dendron substituents, the dendrimers exhibited highly efficient fluorescence emission with mutual cis–trans isomerization. Along with an increase in the generation of dendrons, decrease of Φiso and shortening of τS were observed, suggesting that dendrons affect cis–trans photoisomerization and deactivation from excited singlet state.

Dy^3+ doped borate glasses for laser illumination

Intense multi-peak warm yellowish-white fluorescence emissions of Dy3+ are exhibited in alkaline-earth borate glasses under the excitation of a blue laser. The net emission power and net emission photon number are identified to be 498.23μW and 14.28 × 1014cps, respectively, and the quantum yield is as high as 23.10% in 2.0wt% Dy2O3 doped alkaline-earth borate glass under the excitation of a 453nm blue laser with 14.13mW power. Anticipation of fluorescence color reveals that white luminescence can be achieved when the intensity ratio between residual laser light and Dy3+ emission reaches the appropriate range. By the introduction of Ce3+, the excitation wavelength range and the emission intensity of Dy3+ in alkaline-earth borate glasses are expanded to UVB region and improved by a maximum sensitization factor of 38.2, respectively, demonstrating the utilizability of a UV pumping laser for Ce3+−Dy3+ codoped alkaline-earth borate glasses. Efficient fluorescence emission and realizable white lighting in Dy3+ doped alkaline-earth borate glasses under the laser excitation will promote the development of laser illumination devices.

New near-infrared dyes light up deep tissue imaging.

A newly synthesized class of near-infrared dyes offers strong absorption and efficient fluorescent emission for deep-tissue molecular imaging applications.

Mild preparation and high fluorescence emission efficiency of europium-doped gallium nitride nanocrystals and first-principles density functional theoretical analysis of optical properties

Eu:GaN nanocrystals have strong fluorescence emission and efficient energy transfer by means of DFT simulations. SiO2 coating improves the fluorescence quantum yield.

Growth and spectral analysis of piperazinium l-tartrate salt: A combined experimental and theoretical approach

This report discusses crystal structure, molecular arrangements, vibrational analysis, UV-Vis-NIR spectrum, fluorescence emission and second harmonic generation (SHG) efficiency of piperazinium l-tartrate (PPZ2+·Tart2−) crystals with the support of theoretical analysis. A good optical quality PPZ2+·Tart2− crystals were grown from slow evaporation of aqueous solution. The PPZ2+·Tart2− crystal belongs to monoclinic system with non-centrosymmetric space group P21. The charge transfer from donor to acceptor moieties and corresponding changes in the bond lengths and bond angles have been observed. The observed functional group vibrations in the experimental FTIR and the Raman spectrum were assigned and compared with theoretical wavenumbers of PPZ2+·Tart2−.The electron distribution on the donor and acceptor in PPZ2+·Tart2− has been clearly visualised using molecular electrostatic potential map. Compared with l-tartaric acid, red shift was observed in absorption and fluorescence spectrum. The low value of dielectric constant and dielectric loss at the higher frequency and its high second harmonic efficiency suggest PPZ2+·Tart2− crystal is less defect free and suitable for NLO applications.

Dendron‐Enhanced Emission from 1,4‐Bis[2,2‐bis(4‐alkoxyphenyl)vinyl]benzene Derivatives

AbstractA series of peripheral dendron‐incorporating 1,4‐bis[2,2‐bis(4‐alkoxyphenyl)vinyl]benzenes with aggregation‐induced emission properties were synthesized. As the generation of the dendrons increased, there was an enhancement in the fluorescence emission of the corresponding fluorophore not only in the solid state but also in various solvent systems. The fluorescence quantum yields of the molecule with the largest dendons were up to 71 % in the solid state and 66 % in solution. The dendrons acted as a shell to the fluorophore core to prevent intermolecular π–π interactions and restrict the intramolecular rotations of the fluorophore, which improved the luminous intensity. This study shows that the incorporation of bulky dendrons is an effective way to increase the fluorescence emission efficiency of aggregation‐induced emission fluorophores.

Photoluminescence Enhancement of Silole-Capped Silicon Quantum Dots Based on Förster Resonance Energy Transfer.

Photoluminescent porous silicon were prepared by an electrochemical etch of n-type silicon under the illumination with a 300 W tungsten filament bulb for the duration of etch. The red photoluminescence emitting at 650 nm with an excitation wavelength of 450 nm is due to the quantum confinement of silicon quantum dots in porous silicon. HO-terminated red luminescent PS was obtained by an electrochemical treatment of fresh PS with the current of 150 mA for 60 seconds in water and sodium chloride. As-prepared PS was sonicated, fractured, and centrifuged in toluene solution to obtain photoluminescence silicon quantum dots. Dichlorotetraphenylsilole exhibiting an emission band at 520 nm was reacted with HO-terminated silicon quantum dots to give a silole-capped silicon quantum dots. The optical characterization of silole-derivatized silicon quantum dots was investigated by UV-vis and fluorescence spectrometer. The fluorescence emission efficiency of silole-capped silicon quantum dots was increased by about 2.5 times due to F6rster resonance energy transfer from silole moiety to silicon quantum dots.

Synthesis and physical properties of carbonylated chlorophyll derivatives

Methyl pyropheophorbide-a, one of the chlorophyll-a derivatives, was modified to chlorins possessing/lacking oxo groups at the peripheral 31-, 81-, and 131-positions. Since the carbonyl groups were directly conjugated with the chlorin π-system in a molecule, such electron-withdrawing groups affected visible absorption and fluorescence emission spectra, emission efficiencies, and emission lifetimes as well as oxidation potentials of the semi-synthetic chlorophyll derivatives in a solution. The substitution effect was dependent on the connecting positions.

A fluorescent aptasensor for H5N1 influenza virus detection based-on the core–shell nanoparticles metal-enhanced fluorescence (MEF)

A fluorescent aptasensor system has been designed for the sensitive detection of recombinant hemagglutinin (rHA) protein of the H5N1 influenza virus in human serum. Guanine-richen anti-rHA aptamers by SELEX were immobilized on the surface of the Ag@SiO2 nanoparticles which performed as a metal-enhanced fluorescence (MEF) sensing platform. Thiazole orange (TO) was used as fluorescent tag which reported to the G-quadruplex secondary structural induced by aptamer-rHA binding event. In the absence of rHA protein, TO was free in the solution with almost no fluorescence emission. When rHA protein was added to the solution, the aptamer strand bound rHA protein to form a stable G-quadruplex complex, which can bind TO and excite the fluorescence emission of TO. Moreover, the excited-state TO captured by the G-quadruplex complex was forced to the surface of the Ag@SiO2 nanoparticles and could experience a surface plasmon resonance enhancement which can be transformed into more efficient fluorescence emission signals, therefore, the fluorescence signal of TO can be amplified largely. This system does not require covalent labeling with fluorophores to the aptamer and the background noise is very low. The detection of rHA protein of the H5N1 influenza virus could be operated both in aqueous buffer and human serum with the detection limit of 2 and 3.5ng/mL respectively. More important, the whole detection process can be finished in a PE tube within 30min, which makes it suitable as a self-contained diagnostic kit for H5N1 influenza virus point-of-care (POC) diagnostic.

Si-Doped Carbon Quantum Dots: A Facile and General Preparation Strategy, Bioimaging Application, and Multifunctional Sensor

Heteroatom doping of carbon quantum dots not only enables great improvement of fluorescence efficiency and tunability of fluorescence emission, but also provides active sites in carbon dots to broaden their application in sensor. Silicon as a biocompatible element offers a promising direction for doping of carbon quantum dots. Si-doped carbon quantum dots (SiCQDs) were synthesized through a facile and effective approach. The as-prepared Si-doped carbon quantum dots possess visible fluorescence with high quantum yield up to 19.2%, owing to fluorescence enhancement effect of introduced silicon atoms into carbon dots. The toxicity test on human Hela cells showed that SiCQDs have lower cellular toxicity than common CQDs, and bioimaging experiments clearly demonstrated their excellent biolabelling ability and outstanding performance in resistance to photobleaching. Strong fluorescence quenching effect of Fe(III) on SiCQDs can be used for its selective detection among general metal ions. Specific electron transfer between SiCQDs and hydrogen peroxide enables SiCQDs as a sensitive fluorescence sensing platform for hydrogen peroxide. The subsequent fluorescence recovery induced by removal of hydrogen peroxide from SiCQDs due to formation of the stable adducts between hydrogen peroxide and melamine was taken advantage of to construct effective sensor for melamine.

Triplet Exciton Dynamics in Fluorene−Amine Copolymer Films

Effect of aromaticity on triplet exciton dynamics was studied by transient absorption spectroscopy for two fluorene-based random copolymers with different aromatic amine, poly(9,9′-di-n-octylfluorene-ran-N,N′-bis(4-n-butylphenyl)-N,N′-diphenyl-1,4-benzenediamine) (F8-PDA) and poly(9,9′-di-n-octylfluorene-ran-N,N′-bis(4-t-butylphenyl)-N,N′-diphenyl-9,10-anthracenediamine) (F8-ADA). On a time scale of nanoseconds, triplet exciton was efficiently formed in F8-PDA through the intersystem crossing (ISC) from singlet exciton with a rate constant of 2.0 × 108 s–1. On the other hand, the ISC was not efficient in F8-ADA, resulting in efficient fluorescence emission. On a time scale of micro- to milliseconds, F8-PDA exhibited bimolecular triplet exciton decay due to triplet–triplet annihilation (TTA), but the TTA was negligible in F8-ADA, indicating that triplet excitons can diffuse freely in F8-PDA while they are trapped at ADA units in F8-ADA. The difference in the ISC efficiency and triplet exciton diffusion is ...

Synthesis of chlorophyll–amino acid conjugates as models for modification of proteins with chromo/fluorophores

A chlorophyll-a derivative bonded directly with epoxide at the peripheral position of the chlorin π-system was reacted with N-urethane and C-ester protected amino acids bearing an alcoholic or phenolic hydroxy group as well as a carboxy group at the residue to give chlorophyll–amino acid conjugates. The carboxy residues of N,C-protected aspartic and glutamic acids were esterified with the epoxide in high yields. The synthetic conjugates in dichloromethane had absorption bands throughout the visible region including intense red-side Qy and blue-side Soret bands. By their excitation at the visible bands, strong and efficient fluorescence emission was observed up to the near-infrared region. The chromo/fluorophores are promising for preparation of functional peptides and modification of proteins.