Abstract  Four novel naphthalimide-based dyes (D-1, D-2, D-3 and D-4) were synthesized and utilized as sensitizers in dye-sensitized solar cells (DSCs), in which the triphenylamine (TPA) or indoline groups, naphthalimide unit and carboxylic group were functionalized as electron donor, acceptor and anchoring group, respectively. The naphthalimide unit was employed as the pi-conjugation ring and electron acceptor for effectively realizing intramolecular charge separation in the oxidized states. In the series of dyes, the LUMO orbital is delocalized mainly on naphthalimide moieties, especially on the carbonyl group. Consequently, the LUMO electrons are isolated from the carboxyl anchoring group (-CH2CO2H) due to the presence of the methylene group, which could suppress the electron injection efficiency from the excited dyes to the TiO2 conduction band, thus leading to the inferior efficiencies of 1.10, 1.18, 2.27 and 2.70%, respectively, even though they exhibit broad spectral response and high extinction coefficients. (C) 2011 Elsevier Ltd. All rights reserved.

Abstract  We report the first experimental example, to our knowledge, of reversible switching between a molecular and a charge transfer phase in an organic semiconductor. An oriented film of liquid crystal perylene diimide molecules reversibly switches between a red phase with narrow conduction and valence bands and a large bandwidth black phase as the pi-stacked chromophores shift just 1.6 angstrom relative to their neighbors. This shift causes a substantial change in the intermolecular electronic overlap between molecules. The polarization of maximum absorbance rotates similar to 90 degrees, from an apparently molecule centered transition to an intermolecular charge transfer (CT) transition polarized along the pi-pi stacking axis. The experimental results are further explored via density functional theory calculations on a dimer model that demonstrate the variations in energy and oscillator strength of the molecular (Frenkel) and CT transitions as the longitudinal molecular offset is varied. These results demonstrate the exquisite sensitivity of the electrical properties of organic semiconductors to slight variations in molecular stacking.

Abstract  In the present work, we investigated the bias stress (BS) effect taking place in inkjet-printed n-type N,N'-bis(n-octyl)-1,6-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI8-CN2) transistors fabricated on SiO2 gate dielectric. PDI8-CN2 films were deposited from solvent systems able to improve the layer structural uniformity. These devices were found to exhibit largely negative threshold voltages (V-th) and operate both as accumulation- and depletion-mode transistors. Hence, the BS phenomenon was analyzed by recording the I-DS(t) time curves when the devices were driven under both negative and positive gate-source voltages (V-GS). The BS measurements performed in this work confirm the conventional decay of the I-DS(t) when positive V-GS values (charge accumulation regime) are applied. On the other hand, I-DS(t) increases very rapidly when the devices are polarized with negative V-GS (charge depletion regime). The data achieved for the inkjet-printed devices were also compared with those measured under the same stressing conditions for a device fabricated by evaporating PDI8-CN2 on the same SiO2 substrate type. All the experimental observations reported in this work support the validity of a recently-proposed model, prompting for the occurrence of electrochemical reactions involving PDI8-CN2 molecules and ambient agents (i.e. O-2 and H2O) as origin of the BS phenomenon in these n-type field-effect transistors. (C) 2013 Elsevier B.V. All rights reserved.

Abstract  The controlled self-assembly of precise and well-defined photochemically and electrochemically active carbohydrate-coated nanoparticles offers the exciting prospect of biocompatible catalysts for energy storage/conversion and biolabeling applications. Here an aqueous nanoparticle system has been developed with a versatile outer layer for host-guest molecule encapsulation via β-cyclodextrin inclusion complexes. A β-cyclodextrin-modified polystyrene polymer was first obtained by copper nanopowder click chemistry. The glycopolymer enables self-assembly and controlled encapsulation of tetrazine-naphthalimide, as a model redox-active agent, into nanoparticles via nanoprecipitation. Cyclodextrin host-guest interactions permit encapsulation and internanoparticle cross-linking for the formation of fluorescent compound and clustered self-assemblies with chemically reversible electroactivity in aqueous solution. Light scattering experiments revealed stable particles with hydrodynamic diameters of 138 and 654 nm for nanoparticles prepared with tetrazine, of which 95% of the nanoparticles represent the smaller objects by number. Dynamic light scattering revealed differences as a function of preparation method in terms of size, 3-month stability, polydispersity, radius of gyration, and shape factor. Individual self-assemblies were visualized by atomic force microscopy and fluorescence microscopy and monitored in real-time by nanoparticle tracking analysis. UV-vis and fluorescence spectra provided insight into the optical properties and critical evidence for host-guest encapsulation as evidenced by solvachromatism and enhanced tetrazine uptake. Cyclic voltammetry was used to investigate the electrochemical properties and provided further support for encapsulation and an estimate of the tetrazine loading capacity in tandem with light scattering data.

Abstract  Two novel fluorescent brightening agents (compounds 3a-b shown in Figure 1) were synthesized, using a facile three-step synthetic route, from 4,4'-diamino-2,2'-disulfonic-stilbene, cyanuric chloride, and a readily cross-linkable 3-aminopropyltrimethoxy silane. The products contain hydrolytically active trimethoxysilyl, (-Si(OCH)(3)), functional groups that readily hydrolyze in the presence of water, and subsequently generate a water insoluble silicon cross-linked-network (Si-O-Si) via a condensation process. The cross-linked product hydrolyzes on treatment with hot aqueous sodium hydroxide to silanols (-Si(OH)(3)) to form compounds 4a-b which are readily water soluble and produce a clear fluorescent solution. The silanol forms of compounds 4a-b were used for further characterization and performance evaluation. The structures of compounds 4a-b were characterized by H-1-NMR, Fourier-Transform infrared (FT-IR) spectroscopy and negative electrospray ionization mass (-ESI-MS) spectroscopy. Compounds were applied to cotton fiber as fluorescent brightening agents and their performance was evaluated by measuring the degree of whiteness, ultraviolet protection factor (UPF), fluorescence and acid fastness. Results showed that application of 0.25% (o.w.f) of compounds 4a-b impart a high degree of whiteness (CIE WI = 144, 139) as well as good ultraviolet protection factor (UPF = 29, 27) on cotton fiber exhibiting a significant increase in whiteness and UV blocking properties compared to untreated substrate (CIE WI = 81, UPF = 5). Acid fastness tests of both compounds showed a slight change in fluorescence emission intensities as a function of pH. In acidic solutions, a shift in emission maximum occurs at pH 3 from 434 to 453 nm and from 435 to 457 nm, due to the protonation of amino and sulfonic groups of stilbene fluorophore which substantially reduces the quenching process. Published by Elsevier Ltd.

Abstract  Radical anions in the excited states can be treated as stronger reductants than those in the ground states. In this study, the intramolecular electron transfer (ET) processes from the excited perylene-3,4,9,10-tetracarboxydiimide radical anion (PDI center dot-*) were examined for the first time by applying the femtosecond laser flash photolysis to the dyads of PDI and acceptors (PDI-A). Efficient intramolecular ET from PDI center dot-* was detected upon the excitation of PDI(center dot-)p-yromellitimide (PI) and PDI center dot- naphthalenediimide (NDI) because of the sufficient driving forces. In particular, unprecedented ET processes were confirmed in a PDI-PDI dimer. Excitation of PDI center dot--PDI gave the shortest PDI center dot-* lifetime due to the fastest intramolecular ET. Surprisingly, an intramolecular disproportionation reaction generating the dianion of PDI and neutral PDI was confirmed upon the excitation of PDI center dot--PDI center dot-. These processes successfully simulated the photocarrier (polaron and bipolaron) generations in PDI-based n-type semiconducting materials for various organic molecular devices. Comparing the NDI-A and PDI-A dyad systems, the significant difference found in the intramolecular ET rate constants can be explained by the energy required to form the reduced spacer and the distances between the electron donors and acceptors.

Abstract  Enhancement of fluorescence from single molecules of perylene diimide (PDI) on tantalum pentoxide (Ta2O3) two-dimensional photonic crystal (PC) slabs with low background emission was observed using a single-molecule fluorescence spectroscopy technique. The fluorescence intensity of the single molecules on the PC was more than 3 times higher than that of the molecules without the PC. The performance of the PC slabs with a 100 x objective lens was evaluated by steady-state and time-resolved ensemble fluorescence measurements. The mechanism of the enhancement was attributed to coupling of an excitation laser and fluorescence to the PCs' modes. The present results yield new insights into a highly sensitive investigation of single molecules and regulation of fluorescence emission from them via the effect of PCs.

Abstract  Organic photodiodes are presented that utilize solution-processed perylene diimide bulk heterojunctions as the device photoactive layer. The polymer (9,9'-dioctylfluorene-co-benzothiadiazole; F8BT) is used as the electron donor and the N,N'-bis(1-ethylpropyl)-3,4,9,10-perylene tetracarboxylic diimicle (PDI) derivative is used as the electron acceptor. The thickness-dependent study of the main device parameters, namely of the external quantum efficiency (EQE), the short-circuit current (I(SC)), the open-circuit voltage (V(OC)), the fill factor (FF), and the dark current (I(D)) is presented. In as-spun F8BT:PDI devices the short-circuit EQE reaches the maximum of 17% and the Voc value is as high as 0.8 V. Device I(D) is in the nA mm(-2) regime and it correlates with the topography of the F8BT:PDI layer. For a range of annealing temperatures I(D) is monitored as the morphology of the photoactive layer changes. The changes in the morphology of the photoactive layer are monitored via atomic force microscopy. The thermally induced coalescence of the PDI domains assists the dark conductivity of the device. I(D) values as low as 80 pA mm(-2) are achieved with a corresponding EQE of 9%, when an electron-blocking layer (EB) is used in bilayer EB/F8BT:PDI devices. Electron injection from the hole-collecting electrode to the F8BT:PDI medium is hindered by the use of the EB layer. The temperature dependence of the I(D) value of the as-spun F8BT:PDI device is studied in the range of 296-216 K. In combination with the thickness and the composition dependence of to, the determined activation energy E(a) suggests a two-step mechanism of I(D) generation; a temperature-independent step of electric-field-assisted carrier injection from the device contacts to the active-layer medium and a thermally activated step of carrier transport across the device electrodes, via the PDI domains of the photoactive layer. Moreover, device I(D) is found to be sensitive to environmental factors.

Abstract  Four new monomer dyes, triazinylaminobenzanthrone derivatives, three of them containing a 2-hydroxybenzotriazole fragment, were synthesized. Two new polymerizable triazinylamino-benzotriazole stabilizers have been obtained as well. Two different synthetic routes for their synthesis have been experimented in order to find the better one. The course of the synthesis was monitored using a quantitative thin-layer chromatography (TLC). A benzanthrone dye, suitable for "one-step - in mass" coloration and stabilization of polymers, containing a tetramethylpiperidine (TMP) fragment, following a new approach, was synthesized. The compounds were characterized by TLC analysis, UV/vis, IR and H-1 NMR spectra. The ability of the derivatives to copolymerize with methylmethacrylate (MMA) was demonstrated, thus polymers with an intense color and fluorescence stable to solvents, were obtained. The quantity of the dye chemically bonded in polymer was estimated. A new approach for the synthesis of a benzanthrone dye containing a tetramethylpiperidine fragment suitable for "one-step" in mass coloration and stabilization of polymers was demonstrated. (c) 2006 Elsevier Ltd. All rights reserved.

Abstract  A new class of small molecules based on dicyanodistyrylbenzene combined with naphthalimide is developed for use as non-fullerene electron acceptors in bulk heterojunction organic solar cells. The optical, electrochemical, and film formation characteristics of the new materials are found to be suitable for preparing solution-processed devices. Solar cells prepared with poly(3-hexylthiophene) (P3HT) as a donor material exhibit a maximum power conversion efficiency of 2.71%.

Abstract  Diketopyrrolopyrrole (DPP)-based conjugated polymers have been successfully applied in high performance field-effect transistors and fullerene-based solar cells, but show limited application in non-fullerene solar cells. In this work, we use four DPP polymers as electron donor and a perylene bisimide dye as electron acceptor to construct non-fullerene solar cells. The donors and acceptor have complementary absorption spectra in visible and near-infrared region, resulting in broad photo-response from 300 nm to 1000 nm. The solar cells were found to provide relatively low power conversion efficiencies of 1.6-2.6%, which was mainly due to low photocurrent and fill factor. Further investigation reveals that the low performance is originated from the high charge recombination in photo-active layers. Our systematical studies will help better understand the non-fullerene solar cells based on DPP polymers and inspire new researches toward efficient non-fullerene solar cells with broad photoresponse. (C) 2016 Elsevier B.V. All rights reserved.

Abstract  Self-aggregation behavior in aqueous medium of four naphthalimide derivatives has exhibited substitution-dependent, unusual, aggregation induced emission enhancement (AIEE) phenomena. Absorption, emission, and time-resolved study initially indicated the formation of J-type fluorescent organic nanoaggregates (FONs). Simultaneous applications of infrared spectroscopy, theoretical studies, and dynamic light scattering (DLS) measurements explored the underlying mechanism of such substitution-selective aggregation of a chloro-naphthalimide organic molecule. Furthermore, transmission electron microscopy (TEM) visually confirmed the formation of ring like FONs with average size of 7.5-9.5 nm. Additionally, naphthalimide FONs also exhibited selective and specific cysteine amino acid sensing property. The specific behavior of NPCl aggregation toward amino acids was also employed as a molecular logic gate in information technology (IT).

Abstract  Herein, we design and synthesize a perylene diimide derivative with a fully fused backbone, FITP, which possesses an elevated lowest unoccupied molecular orbital level and high electron mobility. Consequently, polymer solar cells with FITP as the acceptor can provide the best efficiency of 7.33% with a high voltage of 0.99 V.

Abstract  Polymeric nanoparticles (NPs) with two-photon (TP) activity were prepared by grafting a naphthalimide fluorophore onto poly(acrylic acid) to yield an amphiphilic polymer, which self-assembled in water. The NPs were characterized using various analytical techniques such as transmission electron microscopy, dynamic light scattering and spectroscopic measurements. The in vitro and in vivo biocompatibilities of the NPs were assessed by a cytotoxicity assay using HeLa cells and a feeding assay using Caenorhabditis elegans (C. elegans) as a small animal model, respectively. Finally, TP fluorescence imaging (FI) of living cells and C. elegans labelled with the NPs were observed by TP confocal microscopy. The experimental outcomes demonstrated that the NPs had sufficient water-dispersity and biocompatibility, had TP fluorescence activity, were resistant to pH variation and illumination, and were physically stable. TP FI revealed that the NPs could enter living cells and were primarily located in the cytoplasm. In addition, the NPs were ingested by C. elegans during the feeding process and were recognized and taken up by the active transport system of the intestinal cells. These findings indicated the feasibility of using the developed NPs as a nanolabel for TP FI. Moreover, with numerous modifiable carboxyl groups on its surface, the NPs could act as a platform to build multifunctional probes for potential applications in biosensing and assay labeling.

Abstract  Two dimensional conjugated polymers have emerged as excellent polymer donor components in recent years. Here, all-polymer solar cells based on two conjugated side-chain isolated polythiophene derivatives (PT4TV and PT4TV-C) as donors and perylene diimide (PDI)-based polymer (PPDI-DTT) as acceptor are fabricated and investigated in detail. The structure similarity of the two polymers provides more insightful structure-property relationships. PT4TV based device displays a power conversion efficiency (PCE) of 0.99%, higher than that of PT4TV-C based device (0.55%). The high fill factor of larger than 50% in PT4TV based device is ascribed to the balanced hole and electron mobility of the donor and the acceptor. By adding chloronaphthalene solvent in PT4TV: PPDI-DTT solution, the PCE of PT4TV based solar cells is enhanced to 1.17%. Such improvement is interpreted in terms of the refined morphology of the film and ideality factor of the solar cell diode. (C) 2013 Elsevier B.V. All rights reserved.

Abstract  We report an easy-to-prepare fluorescent chemosensor, 4-benzoylamido-N-butyl-1,8-naphthalimide, which is sensitive to fluoride ions. The sensor shows spectral shifts and intensity changes in the presence of fluoride, in a wavelength-ratiometric and -colorimetric manner, which can detect fluoride concentrations in a range of 20-100 mu M at visible wavelengths. The striking colorless-to-yellow color change and blue-to-orange emission color change are thought to be due to the deprotonation of the 4-amido moiety of the naphthalimide fluorophore. The sensor compound shows great promise for the selective detection of fluoride in the presence of other halides because none of those are likely to deprotonate the amide.

Abstract  We developed a series of highly efficient blue electroluminescent polymers with dopant-host systems and molecular dispersion features by selecting 1,8-naphthalimide derivatives as the light blue emissive dopant units, choosing polyfluorene as the deep blue emissive polymer host and covalently attaching the dopant units to the side chain of the polymer host. The polymers' EL spectra exhibited both deep blue emission from the polymer host and light blue emission from the dopant units because of the energy transfer and charge trapping from the polymer host to the dopant units. By modifying the chemical structures of the dopant units, we controlled the energy transfer and charge trapping from the polymer host to the dopant units and consequently tuned the emission colors of the resulting polymers. Thermally annealed single-layer devices (ITO/PEDOT/polymer/Ca/Al) based on these polymers emitted deep blue light with a luminous efficiency of 2.89 cd A(-1), a power efficiency of 2.01 lmW(-1) and CIE coordinates (0.16, 0.17), or emitted sky-blue light with a luminous efficiency of 6.84 cd A(-1), a power efficiency of 4.28 lm W-1 and CIE coordinates (0.15, 0.22). Their excellent EL performances were due to the energy transfer and charge trapping from the polymer host to the highly fluorescent dopant units.

Abstract  Fluorescent probes for hydrogen sulfide have received considerable attention because of the biological significance of H2S recognized recently. Two-photo microscopy offers advantages of increased penetration depth, localized excitation, and prolonged observation time. However, two-photon fluorescent probes for H2S are still rare. In this work, we introduced a dinitrophenyl ether group into the 4-position of 1,8-naphthalimide, which acts as the H2S reactive site, to efficiently yield compound NI-NHS as a two-photo fluorescent probe for H2S. The probe NI-NHS has a high selectivity for H2S over competitive anions and sulfide-containing analytes. This probe exhibits turn-on fluorescence detection of H2S in bovine serum and two-photon fluorescent imaging of H2S in living cells. (C) 2013 Elsevier Ltd. All rights reserved.

Abstract  In this work, a new asymmetrically five-membered O-heterocyclic annulated perylene diimide (O-PDI) has been synthesized. The compounds O-PDI and asymmetrically five-membered S-heterocyclic annulated perylene diimide (S-PDI) self-assembled into nanoneedle and nanosheet, respectively. Photo physical, electrochemical and thermal properties were investigated by UV-vis absorption, fluorescence, cyclic voltammetric, thermogravimetric and differential scanning calorimetry techniques. Optical, fluorescence, scanning and transmission electron microscopies were employed in the molecular self assembly studies. Due to significant electronic coupling between their heteroatom/heterocycles and perylene diimide (PDI) cores, the intermolecular pi-pi actions are neglectable, providing high luminescence efficiency. At the same time, the space between perylene chromophores is still very short (3.3 angstrom for O-PDI and 3.23 angstrom for S-PDI), which is favorable for the hopping transportation of charge carrier from one molecule to a neighboring one. These compounds could be candidate materials for acquiring well defined organic nanostructures with both excellent charge-transporting and good light-emitting capabilities. (C) 2016 Elsevier Ltd. All rights reserved.

Abstract  When isolated conjugated polymer (CP) chains are studied by single molecule spectroscopy, excitation power density in the range of 10-1000 W cm(-2) is normally used. We show that at such excitation power densities the fluorescence ability of CPs is significantly reduced. A new methodological approach allowed us to measure the fluorescence quantum yield (QY) of thin matrix polymer films doped with fluorophores at very low concentration using fluorescence microscopy. Fluorescence QYs of different conjugated polymers (P3HT, MEH-PPV, PFBV and cyclodextrin-coated PFBV-Rtx) and a reference perylene diimide dye dispersed in the PMMA matrix were measured as a function of the excitation power density that ranged from similar to 10(-4) to 100 W cm(-2). Already at an excitation power of 0.1 W cm(-2) (the power density of the sunlight at the Earth) a detectable reduction of the fluorescence QY was observed for most of the polymers. The origin of the QY reduction is exciton annihilation by photo-generated triplet and/or change-transfer states. Insulation by cyclodextrin was found to decrease significantly the effect of non-emissive quenching states.

Abstract  A series of naphthalimides has been synthesized; 2,6-dimethyl-2,3H-furo[2,3-b][1]naphtho[4a,7a-e,f]pyrida-5,7-dione was obtained in a one-pot synthesis through the rearrangement and acidification of N-methyl-4-allyloxy-1,8-naphthalimide. The absorption and fluorescence of these furonaphthalimides and their precursors were recorded.

Abstract  Stimulated by strongly directional C-I center dot center dot center dot N noncovalent halogen bonding, pi-hole center dot center dot center dot pi and pi-pi interactions, cocrystals of nonplanar 4-arylated-2,2'-bipyridine (ArB) derivatives with 1,4-diiodo-tetrafluorobenzene (D) were generated which exhibit a promising columnar/lamellar packing arrangement. Hirshfeld surface, quantum theory of atoms in molecules, and electrostatic potential surface analyses were employed to examine the weak intermolecular interactions governing the packing arrangement in ArB crystals and corresponding cocrystals with D (ArB center dot D). Cocrystals of 4-phenyl-2,2'-bipyridine (PhB) and 4-(naphthalen-1-yl)-2,2'-bipyridine (NaB) with D [PhB center dot D1, PhB center dot D2, (NaB)(2)center dot D-2,D-5, and (NaB)(3)center dot D-2] exhibited C-I center dot center dot center dot N directed infinite one-dimensional chains of alternate ArB and D units. In contrast, C-I center dot center dot center dot Ninteraction's guide the formation of termolecular complexes in the cocrystal of 4-(phenanthren-9-y1)-2,2'-bipyridine with D (PhenB center dot D-0.5). Successful implementation of C-I center dot center dot center dot N interactions aided, by 2,2'-bipyridine and D enabled the tuning of threedimensional close packing in planar polyaromatic hydrocarbons into a columnar/lamellar arrangement suitable for optoelectronic devices.

Abstract  A series of molecules containing a carboxylic acid and a 1,8-naphthalimide group joined by different linkers (HLC1 = CH2; HLC2 = CH2CH2; HLC3 CH2CH2CH2; HLophen = ortho-C6H4; HLC4 = para-C6H4; HLala, = S-CHCH3) have been prepared and structurally characterized. The structures of HLC1, HLC3, and HLala are similar, with alternating hydrogen bonding of the carboxylic acids and pi center dot center dot center dot pi stacking interactions of the naphthalimide groups assembling the molecules into parallel chains that are linked into sheets by a second set of pi center dot center dot center dot pi stacking interactions. Hydrogen bonding and pi center dot center dot center dot pi stacking interactions of the naphthalimide groups also assemble HLC2 into chains, but the chains are alternately oriented at nearly right angles causing the interchain pi center dot center dot center dot pi stacking interaction to organize the chains in an open three-dimensional structure. Three of these open structural units interpenetrate forming a unique three-dimensional network. The rigid ortho-arene linker in HLophen directs the orientation of the pi center dot center dot center dot pi stacking interaction of the naphthalimide rings to be at 60 degrees; when combined with the hydrogen bonding interactions helical one-dimensional chains form that pack into a unique rhombohedral architecture. In the structure of HLC4 center dot DMF, each acid group is hydrogen bonded with the dimethylformamide (DMF) molecule; the structure contains one-dimensional ribbons supported only by the pi center dot center dot center dot pi stacking interactions from the 1,8-naphthalimide groups. All six molecules show fluorescence in the 432-449 nm region. Overall these structural studies show that the 1,8-naphthalimide supramolecular synthon is extremely versatile because it can simultaneously enter into multiple noncovalent interactions.

Abstract  A general methodology for producing ca. 100 nm core-shell colloidal particles in which the shell has an elevated alkyne functionality and yet remains thermoplastic is presented. The availability of accessible alkyne groups on the surface of the aqueous-phase particles allows for the in situ surface modification of the particles through a copper(I) catalyzed Huisgen 1,3-dipolar cycloaddition with an azide-terminated surface agent. The core is an extensively crosslinked polymer which can be easily removed by dispersing the particles in a solvent and centrifuging and collecting the cores, leaving the solubilized shells. This allows for the complete characterization of the colloidal surface reactions in the absence of the volumetrically dominant core. The technique is demonstrated with a core-shell colloid composed of a 135 nm crosslinked polystyrene (PS) core coated with a ca. 10 nm thick uncrosslinked poly(methyl acrylate-co-propargyl acrylate) shell. Due to the applicability of this technique for generating particles useful in biomedical imaging or drug delivery applications, the core-shell particles are surface modified with a variety of azide-terminated poly(ethylene glycol) (PEG) derivatives, including a poloxamer which was terminated on either end by an azide and a naphthalimide chromophore. The resulting fluorescent particles had an absorbance at 413 nm and peak emission at 525 nm. The PEG derivatives could be attached to the particles at a grafting density of ca. 0.2-0.3 groups/ nm(2).

Abstract  The synthesis and sensing properties of a new fluorescent probe designed to have a 4-amino-1,8-naphthalimide fluorescent platform functionalized with a 3-hydroxy-4-pyridinone bidentate chelating unit at the 4-position and a terminal aliphatic dimethylamino group at the imide site, are reported. The absorption and fluorescence properties of the ligand were investigated in DMSO and in aqueous solution at variable pH and in the presence of increasing concentration of Fe3+, Cu2+ and Zn2+. Analysis of the UV-Vis spectra at variable pH allowed the determination of three pK(a) values (PKa1 = 3.19, pK(a2) = 8.38, pK(a3) = 9.95) and establishment of the corresponding speciation diagram. Fluorescence spectra obtained in the same conditions show that the fluorescence intensity of the probe decreases with increasing pH and are off above pH 9 as a result of photo-induced electron transfer arising from the aliphatic dimethylamino group. Under physiological pH conditions, the probe shows an absorption band centred at 439 nm and emits in the green at lambda = 536 nm. Analysis of UV-Vis and EPR spectra of the ligand in the presence of Fe3+ and Cu2+ is consistent with the formation of the corresponding metal ion complexes. The fluorescence intensity of the ligand is quenched in the presence of variable concentrations of Fe3+, Cu2+ and Zn2+ and under physiological pH conditions the fluorescence of the probe is ca 92%, 88% and 91% quenched in the presence of Fe3+, Cu2+ and Zn2+ respectively. (C) 2013 Elsevier Ltd. All rights reserved.