We report energy-transferring organically modified silica nanoparticles for two-photon photodynamic therapy. These nanoparticles co-encapsulate two-photon fluorescent dye nanoaggregates as an energy up-converting donor and a photosensitizing PDT drug as an acceptor. They combine two features:  (i) aggregation-enhanced two-photon absorption and emission properties of a novel two-photon dye and (ii) nanoscopic fluorescence resonance energy transfer between this nanoaggregate and a photosensitizer, 2-devinyl-2-(1-hexyloxyethyl)pyropheophorbide. Stable aqueous dispersions of the co-encapsulating nanoparticles (diameter ≤ 30 nm) have been prepared in the nonpolar interior of micelles by coprecipitating an organically modified silica sol with the photosensitizer and an excess amount of the two-photon dye which forms fluorescent aggregates by phase separation from the particle matrix. Using a multidisciplinary nanophotonic approach, we show:  (i) indirect excitation of the photosensitizer through efficient two-p...

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Organically modified silica nanoparticles co-encapsulating photosensitizing drug and aggregation-enhanced two-photon absorbing fluorescent dye aggregates for two-photon photodynamic therapy.

This article presents a comprehensive review of recent progress of research dedicated to low-dimensional nanomaterials constructed from functional low-molecular-weight organic compounds, whose optoelectronic properties are fundamentally different from those of their inorganic counterparts. After introducing the development of inorganic and organic macromolecular nanomaterials, we begin with a general review of the construction strategies for achieving both zero-dimensional (OD) and one-dimensional (ID) nanostructures from small organic functional molecules. We then provide an overview of the unique optoelectronic properties induced by molecular aggregation in the nanostructures. Special emphasis is put on the luminescent properties that are different from those of the corresponding bulk materials, such as aggregation-induced enhanced emission, fluorescence narrowing, multi-color emission, and tunable and switchable emissions from doped nanostructures. We conclude with a summary and our personal view of the direction of future development of organic opto-functional nanomaterials and devices.

Low-Dimensional Nanomaterials Based on Small Organic Molecules: Preparation and Optoelectronic Properties†

Recent developments in the area of H-bonded supramolecular assemblies of π-conjugated systems, that is, oligomers and polymers, are described. The state-of-the-art summary of the recent developments in the design of discrete systems and functional materials is presented.

Hydrogen-bonded Supramolecular π-Functional Materials†

Aggregation-induced emission (AIE) has attracted considerable interest over the last twenty years. In contrast to the large number of available reviews focusing specifically on AIE, this Essay discusses the AIE phenomenon from a broader perspective, with an emphasis on early observations related to AIE made long before the term was coined. Illustrative examples are highlighted from the 20th century where fluorescence enhancement upon rigidification of dyes in viscous or solid environments or J-aggregate formation was studied. It is shown that these examples already include typical AIE luminogens such as tetraphenylethylene (TPE) as well as stilbenes and oligo- or polyphenylenevinylenes and -ethynylenes, which became important fluorescent solid-state materials in OLED research in the 1990s. Further examples include cyanine dyes such as thiazole orange (TO) or its dimers (TOTOs), which have been widely applied as molecular probes in nucleic acid research. The up to 10 000-fold fluorescence enhancement of such dyes upon intercalation into double-stranded DNA, attributable to the restricted intramolecular motion (RIM) concept, afforded commercial products for bioimaging and fluorescence sensing applications already in the early 1990s.

Aggregation-Induced Emission (AIE): A Historical Perspective.

This paper reports the design, synthesis, and theoretical modeling of two-photon properties of a new class of chromophore that exhibits enhanced two-photon absorption (TPA) and subsequently generated strong up-converted emission in nanoaggregate forms. This chromophore utilizes the basic structural unit of 9,10-bis[4′-(4″-aminostyryl)styryl]anthracene that exhibits large internal rotation in the monomer form in organic solvents, whereby the fluorescence is greatly reduced. In nanoaggregates formed in water, the internal rotation is considerably hindered, leading to significant increases of TPA and fluorescence quantum yield. Theoretical modeling of the conformational structure and dynamics has utilized a semiempirical pm3 formalism. The TPA cross sections of the monomer and the aggregate states have been calculated on the basis of the quadratic response theory applied to a single-determinant self-consistent field reference state making use of a split-valence 6-31G* basis set.

Aggregation‐Enhanced Fluorescence and Two‐Photon Absorption in Nanoaggregates of a 9,10‐Bis[4′‐(4″‐aminostyryl)styryl]anthracene Derivative

Organic nanoparticles of 1,3-diphenyl-5-(2-anthryl)-2- pyrazoline (DAP) ranging in average diameters from 40 to 160 nm were prepared through the reprecipitation method. The average diameters of the particles were controlled by variation of the aging time. We found that DAP nanoparticles exhibit the size-dependent optical properties. The absorption transitions of the nanoparticles at the lower-energy side experience a bathochromic shift with an increase in the particle size as a result of the increased intermolecular interactions, while the higher-energy bands of anthracene split possibly due to the electronic coupling between the pyrazoline ring of one molecule and the anthracene moiety of the neighboring molecule. Most interestingly, the nanoparticle emission in the blue light region from pyrazoline chromophore shifts to shorter wavelengths with an increase in the particle size, accompanied with a relatively gradual dominance of the emission at about 540 nm from an exciplex between the pyrazoline ring of...

Size-tunable emission from 1,3-diphenyl-5-(2-anthryl)-2-pyrazoline nanoparticles.

Organic nanoparticles from a chiral auxiliary, (R)-(+)-1,1'-bi-2-naphthol dimethyl ether (BNDE), with a range of particle sizes from 25 to 100 nm were fabricated through the reprecipitation method. It is found that BNDE nanoparticles exhibit positive exciton chirality in 200-260 nm region in circular dichroism (CD) spectra, which are completely opposite to CD spectra of the dilute solution. The exciton chirality of the particles displays size-dependent behavior; that is, the exciton chirality peaks evolve to the low-energy side with increase in particles size. CD spectra accompanied with UV, fluorescence spectra, lifetime measurements of the excited states, and quantum mechanical calculations reveal that the chirality inversion results from intermolecular exciton coupling between two adjacent BNDE molecules in the nanoparticles, and the bathochromic shift of the peaks is attributed to the increased intermolecular interaction with increasing particle size.

Size-dependent exciton chirality in (R)-(+)-1,1'-bi-2-naphthol dimethyl ether nanoparticles.

CD inversion and fluorescence enhancement in organic nanoparticles of (R)-di-2-naphthylprolinol.

Four novel heptanuclear Ln-Cu complexes with the formula [Ln2Cu(hfac)8(NITPhTzbis)2][LnCu(hfac)5(NITPhTzbis)]2 (LnCu = YCu 1, TbCu 2, DyCu 3 and HoCu 4; hfac = hexafluoroacetylacetonate) were successfully constructed by employing the triazole functionalized nitronyl nitroxide biradical ligand NITPh-Tzbis (NITPh-Tzbis = 5-(1,2,4-triazolyl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene). These hetero-tri-spin complexes are composed of two biradical-bridged dinuclear [(LnCu(hfac)5(NITPhTzbis)] units and one trinuclear [Ln2Cu(hfac)8(NITPhTzbis)2] unit which form a heptanuclear supramolecular structure through π-π interactions. Magnetic susceptibility investigations indicate that ferromagnetic exchange interactions dominate at low temperature for this supramolecular system which can be attributed to the Ln-nitroxide exchange and intramolecular NIT⋯NIT coupling mediated by the m-phenylene moiety. The DyCu derivative was found to exhibit a slow magnetic relaxation behavior.

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Supramolecular heptanuclear Ln-Cu complexes involving nitronyl nitroxide biradicals: structure and magnetic behavior.

Utilizing an hexadentate nitronyl nitroxide biradical bisNITbpym, two series of biradical-4f clusters, namely [Tb2(hfac)6(bisNITbpym)2]·CHCl3 (1), [Dy2(hfac)6(bisNITbpym)2] (2), and [Ln4(hfac)12(bisNITbpym)2] (LnIII = YIII3, TbIII4 and YbIII5) (bisNITbpym = 2,2′-dipyridyl-5,5′-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl); hfac = hexafluoroacetylacetonate), have been smoothly obtained via regulating the ratio of LnIII metal to biradical bisNITbpym. In compounds 1 and 2, the bisNITbpym ligand links two TbIII ions to yield a dinuclear pattern. Meanwhile, 3–5 exhibit an annular tetranuclear structure with biradical bisNITbpym, enwrapping and bridging four LnIII ions. Single-molecule magnet behavior of the Dy derivate is confirmed through frequency-dependent ac signals. Furthermore, this comparative exploration of dinuclear and tetranuclear systems indicates that spatial symmetries around LnIII ions have an important impact on magnetic dynamics. Near-infrared luminescence and slow magnetic relaxation have been observed in the YbIII derivative, which can act as a promising multifunctional probe in the aspect of fluoroimmuno assays. Our present work not only successfully acquires a multifunctional YbIII-based compound but also achieves the regulation of nuclearity and magnetic property of the nitronyl nitroxide biradical-LnIII system. 

Lu Xi

Papers

Size-tunable emission from 1,3-diphenyl-5-(2-anthryl)-2-pyrazoline nanoparticles.

Size-dependent exciton chirality in (R)-(+)-1,1'-bi-2-naphthol dimethyl ether nanoparticles.

CD inversion and fluorescence enhancement in organic nanoparticles of (R)-di-2-naphthylprolinol.

Supramolecular heptanuclear Ln-Cu complexes involving nitronyl nitroxide biradicals: structure and magnetic behavior.

Tuning Nuclearity of Biradical-Ln Functional Compounds with Single-Molecule Magnet Behavior and Near-Infrared Luminescence