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Solid mixture of PbS quantum dot and a directly attached emitter penetrating the ligand layer enables photon upconversion from near infrared.

Steric bulkiness – the metric of the robustness of the self-photosensitized, single metal-active-site catalysis, elucidated in CO2 photoreduction.

Efficiency of photon upconversion (UC) from near infrared (NIR) to visible emission by the triplet-triplet annihilation (TTA) mechanism in solid has been limited to be low in spite of its...

We describe a new type of nitrogen‐centered polycyclic scaffold comprising a unique combination of 5‐, 6‐, and 7‐membered rings. The compound is accessible through an intramolecular oxidative cyclodehydrogenation of tri(1‐naphthyl)amine. To the best of our knowledge this is the very first example of a direct 3‐fold cyclization of a triarylamine under oxidative conditions. The unusual ring fusion motif is confirmed by X‐ray crystallography and the impact of cyclization on the electronic and photophysical properties is investigated both experimentally and theoretically based on density‐functional theory (DFT) calculations. The formation of the unexpected product is rationalized by detailed mechanistic studies on the DFT level. The results suggest the cyclization to occur under kinetic control via a dicationic mechanism.

Here, we present single crystalline capsules of a photoresponsive molecule produced by simple recrystallization from organic solutions without direct human processing. During the crystal growth process, a movie was taken of the capsule taking in the organic solution. The capsules responded rapidly (

Two-photon-excited fluorescent probes are important for two-photon microscopy for biomedical studies. In contrast to the many examples of probes for cationic species, such as metal ions, there have been fewer reports on the control of two-photon optical properties by anions because in such systems it is difficult to control the associated π-electronic states. This Minireview summarizes anion-responsive molecules that exhibit changes in two-photon optical properties and describes their molecular design and anion-response mechanisms, which are driven by changes in covalent bonds and noncovalent interactions. Results from a recent study of two-photon systems, where geometries and optical properties are modulated by anion binding, are also discussed.

A highly efficient tetradentate PNNP-type Ir photocatalyst, Mes-IrPCY2, was developed for the reduction of carbon dioxide. The photocatalyst furnished formic acid (HCO2H) with 87% selectivity toget...

We fabricated polarized near-infrared (NIR) emitting devices using with the oriented films of a low-band-gap-polymer PTB7 (poly{4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']tithiophene-2,6-diyl-alt...

Linear ladder-type π-conjugated molecules have attracted much interest because of their intriguing physicochemical properties. To modulate their electronic structures, an effective strategy is to incorporate main-group elements into ladder-type π-conjugated molecules. In line with this strategy, a variety of ladder-type π-conjugated molecules with main-group elements have been synthesized to explore their potential utility as organic functional materials. In this context, phosphole-based π-conjugated molecules are highly attractive, owing to their unique optical and electrochemical properties, which arise from the phosphorus atom. Herein, the synthesis and physicochemical properties of doubly thiophene-fused benzodiphospholes, as a new class of phosphole-based ladder-type π-conjugated molecule, are reported. Systematic investigations into the physicochemical properties of doubly thiophene-fused benzodiphospholes revealed their pluripotent features: intense near-infrared fluorescence, excellent two-photon absorption property, and remarkably high electron-transporting ability. This study demonstrates the potential utility of doubly thiophene-fused benzodiphospholes as organic functional materials for biological imaging, nonlinear optics, organic transistors, and organic photovoltaics.

In this work, we report the experimental and theoretical first molecular electronic hyperpolarizability (βHRS) of eleven π-conjugated oxazoles compounds in toluene medium. The Hyper-Rayleigh Scattering (HRS) technique allowed the determination of the experimental dynamic βHRS values, by exciting the compounds with a picosecond pulse trains from a Q-switched and mode-locked Nd:YAG laser tuned at 1064 nm. Theoretical predictions based on time-dependent density functional theory level using the Gaussian 09 program package were performed with three different functionals (B3LYP, CAM-B3LYP, and M06-2X), to calculate both static and dynamic theoretical βHRS values. Good accordance was found between the experimental and theoretical values, in particular for the CAM-B3LYP and M06-2X functionals.

Three new perylenetetracarboxy-3,4:9,10-diimides, bearing 2,6-diisopropylphenyl groups at the imide positions and 4-(R-ethynyl)phenoxy moieties (R = 4,7-di(2-thienyl)benzo[c][1,2,5]thiadiazole (P2), pyrene (P3) or pyrene-CH2OCH2 (P4)) at the four bay positions, were prepared, along with the known related derivative (R = phenyl (P1)), and well characterized. They have large two-photon absorption (TPA) cross-sections (σ2), as determined by the Z-scan technique, the highest values being reached with P2 which bears a planar π-delocalized donor moiety. P3 is characterized by higher σ2 values than both P1, as expected for the higher π-conjugation of the donor pyrene moiety with respect to phenyl, and P4, due to the presence of the flexible and non-conjugated CH2OCH2 bridge between the pyrene and the ethynyl fragment in the latter compound. The molecular geometry of P1–P4 has been optimized by DFT modeling, showing that in P2 and P3 the bay substituents are stacked due to the π–π interactions of both pyrene and thiophene groups. The LUMO of P1–P4 lies at the same energy and is essentially delocalized on the perylene core whereas the HOMO and HOMO−1 of both P2 and P3 are degenerate and do not show contribution from the perylene core contrarily to that of P1 and P4. The HOMO–LUMO gap is therefore essentially influenced by the HOMO which reflects the electronic charge delocalization on the bay substituents, the lower gaps being observed for P2 and P3, which are characterized by the best TPA properties.

Two-photon absorption (TPA) dyes with intense fluorescence can be used to detect small chemical species and as sensors and bioimaging probes for specific analytes. Various TPA dyes responding to a number of external stimuli have been reported. Among them, biologically important anionic species have not been used as agents to control TPA properties because their direct electronic influences on the transition dipole moments of dyes are typically small. In this study, dipyrrolyldiketone BF2 complexes substituted with π-extended units exhibited efficient TPA properties that could be regulated by conformation changes induced by anion binding. The TPA intensity decreased to 1/5 of the original intensity upon anion binding, which was much larger than that observed for one-photon absorption. Anion detection was achieved by a change in the emission intensity of spatially resolved spots of two-photon-excited fluorescence (TPEF) in the sample. Experimental and theoretical studies were performed to understand the mechanism of the TPA property control and showed that the drastic changes in the transition dipole moments upon conformation changes between the straight and bending forms of the π-electronic systems caused the TPA and TPEF intensities drop.

Peropyrene is a promising candidate molecule for use in organic solar cells based on singlet fission, because it fulfills the energy matching requirement for singlet fission. We prepare three 2,9-disubstitued peropyrene derivatives and investigate their crystal structures, photophysical properties, and singlet fission phenomenon. Although each derivative shows different molecular overlap motifs in solid state, no singlet fission occurs under normal exciton density conditions due to the substantial stabilization of the first excited singlet (S1) state. In contrast, under high exciton density conditions, singlet fission from highly excited singlet (Sn) states, which is generated by singlet–singlet exciton annihilation, takes place to produce a triplet exciton. We also investigate the reverse process of singlet fission, that is, triplet–triplet annihilation, of peropyrene in solution state to explore the possibility of photon upconversion.

This work reports the study of the second- and third-order nonlinear optical properties of two dibenzylideneacetone derivatives: (1E,4E)-1,5-bis(4-bromophenyl)penta-1,4-dien-3-one (4-DBDBA) and (1E,4E)-1,5-bis(4-chlorophenyl)penta-1,4-dien-3-one (4-DCDBA) in dichloromethane solution. The nonlinear optical properties investigated were the first molecular hyperpolarizability and the two-photon absorption (2PA) cross-section by using the hyper-Rayleigh scattering (HRS) and Z-scan techniques respectively. The values of the first molecular hyperpolarizability obtained by HRS ( β H R S ) were 25 × 10 - 30 c m 4 s t a t v o l t - 1 for 4-DBDBA whereas for 4-DCDBA was 27 × 10 - 30 c m 4 s t a t v o l t - 1 . The peak value for 2PA cross-section by the spectral measurement was around 24 G M for 4-DBDBA and 17 G M for 4-DCDBA. In addition, quantum chemical calculations were performed to support the interpretation from experimental results.

Strapped acceptor–π–donor–π–acceptor type fluorophores exhibit intense near infrared emission, together with near infrared two-photon absorption., Fluorophores that can undergo excited-state intramolecular proton transfer (ESIPT) represent promising scaffolds for the design of compounds that show red-shifted fluorescence. Herein, we disclose new near infrared-emissive materials based on a dialkylamine-strapped 2,5-dithienylpyrrole as an ESIPT scaffold. The introduction of electron-accepting units to the terminal positions of this scaffold generates acceptor–π–donor–π–acceptor (A–π–D–π–A) type π-conjugated compounds. Following the ESIPT, the electron-donating ability of the core scaffold increases, which results in a substantially red-shifted emission in the NIR region, while increasing the oscillator strength. The electron-accepting units play a vital role to achieve intense and red-shifted emission from the ESIPT state. The strapped dialkylamine chain that forms an intramolecular hydrogen bond is also essential to induce the ESIPT. Moreover, an extended A–π–D–π–A skeleton enables two-photon excitation with the NIR light. One of the derivatives that satisfy these features, i.e., borylethenyl-substituted 5, exhibited an intense NIR emission in polar solvents such as acetone (λem = 708 nm, ΦF = 0.55) with a strong two-photon-absorption band in the NIR region.

Three quadrupolar donor–acceptor–donor compounds bearing diketopyrrolopyrroles as a central core and exceptionally electron-rich diarylaminofurans and dialkylaminobenzofuran as donors were designed. Straightforward synthesis afforded these dyes in good overall yield. These donor–acceptor–donor systems turned out to be strong red-emitters with fluorescence extending well into the NIR region. Two-photon brightness (850–1900 GM) was found to be larger than for any previously studied diketopyrrolopyrrole dyes.

In this proof of concept study, we show that intramolecular singlet fission (iSF) can be initiated from a singlet excited state accessed by two-photon absorption, rather than through a traditional route of direct one-photon excitation (OPE). Thus, iSF in pentacene dimers 2 and 3 is enabled through NIR irradiation at 775 nm, a wavelength where neither dimer exhibits linear absorption of light. The adamantyl and meta-phenylene spacers 2 and 3, respectively, are designed to feature superimposable geometries, which establishes that the electronic coupling between the two pentacenes is the significant structural feature that dictates iSF efficiency.

The impact of intermolecular interactions on the third-order nonlinear optical (NLO) properties of open-shell molecular aggregates has been elucidated by considering one-dimensional aggregates of π-π stacked phenalenyl radicals with different intermolecular distances and the long-range corrected spin-unrestricted density functional theory method. In the phenalenyl dimer, which can be considered as a diradicaloid system, the diradical character strongly depends on the intermolecular distance, and the larger the intermolecular distance is, the larger the diradical character becomes. Then, around the equilibrium stacking distance that corresponds to an intermediate diradical character, its second hyperpolarizability (γ) is maximized and its value per monomer exhibits about a 30-fold enhancement with respect to the isolated phenalenyl monomer. This suggests that equilibrium is an optimal compromise between localization and delocalization of the radical electron pairs in such pancake bonding. No such effect was observed for the closed-shell coronene dimer. Moreover, when going from the dimer (diradical) to the tetramer (tetraradical), the γ-enhancement ratio increases nonlinearly with the aggregate size, whereas switching from the singlet to the highest spin (quintet) state causes a significant reduction of γ. Finally, for the tetramer, another one-order enhancement of γ is achieved for the dicationic singlet relative to its singlet neutral state. These results demonstrate the key role of intermolecular π-π stacking interactions and charge in open-shell (supra)molecular systems to achieve enhanced third-order NLO properties.

The edge state, which is a peculiar magnetic state in zigzag-edged graphene nanoribbons (ZGNRs) originating from an electron–electron correlation in an edge-localized π-state, has promising applications for magnetic and spintronics devices and has attracted much attention of physicists, chemists, and engineers. For deeper understanding of the edge state, precise fabrication of edge structures in ZGNRs has been highly demanded. We focus on anthenes, which are peri-condensed anthracenes that have zigzag and armchair edges on the molecular periphery, as model systems for understanding, and indeed prepare and characterize them. This paper summarizes our recent studies on the origin of the edge state by investigating anthenes in terms of the relationship between the molecular structure and spin-localizing character.

The self-assembled boronic ester cavitand capsule 3 quantitatively and tightly encapsulates 2,6-diacetoxy-9,10-bis(arylethynyl)anthracene derivatives 4 a-4 c as highly fluorescent cruciform guests to form complexes 4 a@3, 4 b@3, and 4 c@(3)2. The structural features of capsule 3, which possesses two polar bowl-shaped aromatic cavity ends and four large equatorial windows connected by dynamic boronic ester bonds, made it possible to encapsulate cruciform 4 with protection of the reactive anthracene core inside the capsule and with two protruding arylethynyl groups, the π-conjugated arms of compound 4, through two of the equatorial windows of the capsule. Thus, complexes 4 a@3, 4 b@3, and 4 c@(3)2 show greater resistance to photochemical reactions in solution and fluorescence quenching in the powder state compared to free guests 4. In addition to the improved photostability, restriction of the free rotation of the arylethynyl groups of guests 4 upon encapsulation results in sharpening of the UV/Vis absorption peaks with a red-shift and a significant increase in some of the two-photon-absorption peaks of complexes 4 a@3, 4 b@3, and 4 c@(3)2 compared with free guests 4.

A new porphyrin-perinaphthothioindigo composite, where porphyrin and perinaphthothioindigo dye are connected though a triple bond, was synthesized. In UV-vis absorption spectra of the composite, absorption originating from the trans-isomer appeared at 655 nm. Upon photoirradiation at > 700 nm, the intensity of this absorption decreased with increase of absorption of the cis-isomer around at 530 nm. The HOMO–LUMO absorption of the cis-isomer is blue-shifted by 125 nm compared to that of trans-isomer due to the lack of π-conjugation. The 2PA cross-section values obtained for both isomers were 2,000 and 700 GM, respectively. The value of 2,000 GM is of the largest class among the values reported for photochromic compounds. The enhancement factors by the connection of porphyrin to perinaphthothioindigo were found to be 3.5–3.9 by measuring cross-section values of bis(TMS-ethynyl)perinaphthothioindigo as the reference compound. Two-photon isomerization of the trans-isomer to the cis-isomer was successfully conducted using femtosecond pulses.

We present herein the synthesis and properties of the largest hitherto unknown graphyne fragment, namely trigonally expanded tetrakis(dehydrobenzo[12]annulene)s (tetrakis-DBAs). Intramolecular three-fold alkyne metathesis reactions of hexakis(arylethynyl)DBAs 9 a and 9 b using Fürstner's Mo catalyst furnished tetrakis-DBAs 8 a and 8 b substituted with tert-butyl or branched alkyl ester groups in moderate and fair yields, respectively, demonstrating that the metathesis reaction of this protocol is a powerful tool for the construction of graphyne fragment backbones. For comparison, hexakis(arylethynyl)DBAs 9 c-g have also been prepared. The one-photon absorption spectrum of tetrakis-DBA 8 a bearing tert-butyl groups revealed a remarkable bathochromic shift of the absorption cut-off (λcutoff ) compared with those of previously reported graphyne fragments due to extended π-conjugation. Moreover, in the two-photon absorption spectrum, 8 a showed a large cross-section for a pure hydrocarbon because of the planar para-phenylene-ethynylene conjugation pathways. Hexakis(arylethynyl)-DBAs 9 c-e and 9 g and tetrakis-DBA 8 b bearing electron-withdrawing groups aggregated in chloroform solutions. Comparison between the free energies of 9 e and 8 b bearing the same substituents revealed the more favorable association of the latter due to stronger π-π interactions between the extended π-cores. Polarized optical microscopy observations, DSC, and XRD measurements showed that 8 b and 9 e with branched alkyl ester groups displayed columnar rectangular mesophases. By the time-resolved microwave conductivity method, the columnar rectangular phase of 8 b was shown to exhibit a moderate charge-carrier mobility of 0.12 cm(2) V(-1) s(-1) . These results indicate that large graphyne fragments can serve as good organic semiconductors.

The characteristics of the edge state, which is a peculiar magnetic state in zigzag-edged graphene nanoribbons (ZGNRs) that originates from electron-electron correlation in an edge-localized π-state, are investigated by preparing and characterizing quarteranthene molecules. The molecular geometry that was determined from the X-ray analysis is consistent with a zigzag-edge-localized structure of unpaired electrons. The localized electrons are responsible for the peculiar magnetic (room-temperature ferromagnetic correlation), optical (the lowest-lying doubly excited state), and chemical (peroxide bond formation) behaviors. On the basis of these distinguishing properties and a careful consideration of the valence bonding, insight into the edge state of ZGNRs can be gained.

The first synthesis of an all-benzene carbon nanocage 1, which represents a junction unit of branched carbon nanotubes, has been achieved. A stepwise assembly of six L-shaped units [cis-di(p-bromophenyl)cyclohexane derivative] and two three-way units (1,3,5-triborylbenzene) by cross-coupling and homocoupling provided the unstrained cyclic precursor. Acid-mediated aromatization of cyclohexane moieties in the precursor resulted in the formation of carbon nanocage 1. Photophysical measurements and DFT studies revealed the unique properties of 1, such as D3 symmetry with degenerate HOMO/HOMO − 1 and LUMO/LUMO + 1, high fluorescence quantum yield (ΦF = 0.87), and a relatively large two-photon absorption cross section (500 GM at 590 nm), which are attractive for various applications.

Novel two-photon absorption (TPA) chromophores that contain spirofluorene and ladder-type pentaphenylenes (LPPs) as π-centres with diarylamine groups as electron donors (D) in the D–π–D arrangement are prepared. The spirofluorenes with different donors at the both terminals exhibit TPA activity increase as the donor strength increases (from N-ethylcarbazoyl 1, triphenylamino 2, to N,N-dibutylaminophenyl 3). Compared to the spirofluorene derivatives, the LPP derivatives show the larger TPA efficiency due to better coplanarity throughout the molecule. As the LPP unit added from single (4), double (5), to triple (6), the increment of the TPA cross-section exceeds the one-fold of a LPP unit, which can be attributed to the cooperative enhancement of the TPA cross-section (σ2) between the LPP units. We have also explored the effect of introducing charge defects and examined the resonance enhancement by chemical oxidation on the TPA properties of LPP derivatives 4 and 5. Nearly an order of magnitude enhancement was found in the TPA cross-section of dye 4, which was interpreted as the role of charge transfer from LPP π-centre to the cationic diarylamine end groups.

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. The synthesis of boron difluoride complexes of a series of curcuminoid derivatives containing various donor end groups is described. Time-dependent (TD)-DFT calculations confirm the charge-transfer character of the second lowest-energy transition band and ascribe the lowest energy band to a "cyanine-like" transition. Photophysical studies reveal that tuning the donor strength of the end groups allows covering a broad spectral range, from the visible to the NIR region, of the UV-visible absorption and fluorescence spectra. Two-photon-excited fluorescence and Z-scan techniques prove that an increase in the donor strength or in the rigidity of the backbone results in a considerable increase in the two-photon cross section, reaching 5000 GM, with predominant two-photon absorption from the S0-S2charge-transfer transition. Direct comparisons with the hemicurcuminoid derivatives show that the two-photon active band for the curcuminoid derivatives has the same intramolecular charge-transfer character and therefore arises from a dipolar structure. Overall, this structure-relationship study allows the optimization of the two-photon brightness (i.e., 400-900 GM) with one dye that emits in the NIR region of the spectrum. In addition, these dyes demonstrate high intracellular uptake efficiency in Cos7 cells with emission in the visible region, which is further improved by using porous silica nanoparticles as dye vehicles for the imaging of two mammalian carcinoma cells type based on NIR fluorescence emission.

Large two-dimensional (2D) carbon-rich molecules with defined sizes, shapes, and compositions have attracted considerable attention because of their one-dimensional (1D) stacking in solution, supramolecular 2D crystallinity on surfaces, and optical properties both in solution and in the solid state. In particular, planar cyclic p frames with large inner cavities and long alkyl or alkoxy side chains have been used for the construction of either supramolecular architectures or weakly bound host–guest complexes by the nanoscopic phase separation among the p frame, alkyl moiety, and inner sphere. Thus, large 2D planar condensed aromatics without inner cavities tend to form crystals, liquid crystals, and nanostructures through fairly strong p–p and van der Waals interactions, and the self-association is an enthalpically driven process that is entropically disfavored. In a similar manner, shape-persistent cyclic conjugated molecules with large inner cavities should assemble into supramolecular structures with reduced dimensionality, that is, 1D and 2D nanostructures. However, our preliminary experiments show that their thermodynamic parameters are sometimes different from those of large 2D planar condensed aromatics. We have recently developed a new synthetic method to prepare cyclic oligophenylenes by electrontransfer oxidation of Lipshutz cuprates and reported the synthesis, photophysical properties, and supramolecular architectures of cyclic nonaphenylenes 1a–c (Figure 1). Next, we converted 1a–c into the corresponding triphenylene trimers 2a–c by dehydrogenative bond formation to examine their optical properties and self-assembling behavior. Although 1a–c could be converted into triphenylene trimers 2a–c by using dehydrogenative cyclization, 2a has poor solubility in common organic solvents. Therefore, the optical properties and the formation of nanostructures of 2b,c were investigated and compared with those of 1b,c from a viewpoint of the structure–property relationship. In the case of 1b, fine colorless crystals with high solid-state emission were obtained owing to its nonplanar oligophenylene structure. As for 1c, a fluorescent fibrous material precipitated from a mixture of diisopropyl ether (IPE)/methanol (1:1). The fibers of 1c formed a sheet structure perpendicular to the fiber direction, and the intermolecular distance between the phenyl rings at the apex position was determined to be 4.3 ; this indicated no p–p stacking interactions and a Lego-like interlocking structure. As triphenylene trimers 2b,c have large shape-persistent p frames with long alkyl and alkoxy side chains, 2b,c should show a nanoscopic phase separation and amphiphilicity and, hence, stronger supramolecular self-aggregation. Herein, we report the emission properties and self-aggregation behavior of 2b,c as well as the formation of a dendritic supramolecular architecture comprised of a charge-transfer (CT) complex of 2b and 2,4,7-trinitrofluorenone (TNF). As reported previously, 1b,c were synthesized by using electron-transfer oxidation of Lipshutz cuprates 4b,c prepared from 3b,c in a one-pot procedure (Scheme 1). Although the yields of 1b,c were not high, they were obtained as the major components of the soluble products. Under dehydrogenative cyclization conditions, 1b was treated with CuACHTUNGTRENNUNG(OTf)2 and AlCl3 in CS2 to produce 2b (73%), and 1c was treated with FeCl3 in nitromethane/dichloromethane (3/ [a] Y. Hanai, Dr. M. J. Rahman, Dr. J. Yamakawa, Dr. M. Takase, Prof. T. Nishinaga, Prof. M. Iyoda Department of Chemistry, Graduate School of Science and Engineering Tokyo Metropolitan University Hachioji, Tokyo 192-0397 (Japan) Fax: (+81)42-677-2525 E-mail : iyoda@tmu.ac.jp [b] Dr. M. Hasegawa Department of Chemistry School of Science Kitasato University Sagamihara, Kanagawa 252-0373 (Japan) [c] Dr. K. Kamada Research Institute for Ubiquitous Energy Devices National Institute of Advanced Industrial Science and Technology (AIST) AIST Kansai Center, Ikeda, Osaka 563-8577 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201100336.

The substituent effect on the degree of intramolecular charge transfer (δ) and optical properties of donor acceptor compounds comprised of l,3,3-trimethyl-2-methyleneindoline (I 1 ) and substituted 7,8,8-tricyanoquinodimethane (=2-(4-cyanomethylene-2,5-cyclohexadienylidene)malononitrile, 3CNQ-R, R = substituent groups) moieties were investigated (Ii-3CNQ-R). In the crystal structures, I 1 -3CNQ-R molecules stacked on indoline and/or 3CNQ-R moieties in a head-to-tail manner to cancel their dipole moments and established segregated or mixed stack columnar motifs. The δ values of Ii-3CNQ-R molecules in solid and solution states were estimated using the bond length ratio in the crystal structures, molecular orbital calculation, and the solvatochromic shift of intramolecular charge-transfer absorption, respectively, and showed significant and reasonable dependences on substituents of the 3CNQ moiety. Structural analysis revealed that molecular conformation and planarity affect the δ values of I 1 -3CNQ-R molecules. Molecular orbital calculations revealed that molecular (hyper)polarizabilities can be modulated by tuning δ. I 1 -3CNQ-R exhibited a solvatochromic shift, and the ground state changed from neutral (δ ≤ 0.5) in less-polar solvents to ionic (δ ≥ 0.5) in polar solvents. Two-photon absorption properties of I 1 -3CNQ-R showed a significant substituent effect and indicated that δ is a fundamental parameter for modulating non-linear optical properties.

C. K. acknowledges the HPC resources of CINES and of IDRIS under the allocations 2014-[x2014080649] made by GENCI (Grand Equipement National de Calcul Intensif).; International audience; A new chromophore, 2-(4-nitrophenyl)benzofuran (NPBF), was designed for two-photon (TP) uncaging using near-IR light. The TP absorption (TPA) cross-sections of the newly designed NPBF chromophore were determined to be 18 GM at 720 nm and 54 GM at 740 nm in DMSO. The TP uncaging reaction of a caged benzoate with the NPBF chromophore quantitatively produced benzoic acid with an efficiency (δu) of ∼5.0 GM at 740 nm. The TP fragmentation of an EGTA unit was observed with δu = 16 GM. This behavior makes the new chromophore a promising TP photoremovable protecting group for physiological studies.

Linear (one-photon) and nonlinear (two-photon) spectral properties of 4-N,N-dimethylamino-4′-aminoazobenzene have been investigated under protonation in DMSO/water solvent mixtures. Observed spectral changes have been discussed in terms of ammonium–azonium tautomerism. The corresponding tautomeric constants have been determined for the first time for such kind of tautomeric equilibria. The process of protonation leads to changes of the two-photon absorption properties, suggesting that such process could be used as a tool for change of third-order nonlinear optical activity in solution.

Two-photon absorption(TPA)properties of several linear molecules were experimentally studied and discussed in terms of theirπ-bridge. Asymmetric molecules containing C = C, N = N, and N = Cπ-bridges were examined and found that molecular planarity along theπ-bridge plays an important role on TPA activity. Also symmetric bis(styrylpyridines)derivatives containing a diacetyleneπ-bridge were examined and found to exhibits stronger TPA than the aromaticπ-bridge molecule with similar extent ofπ-conjugation. Drastic enhancement of TPA cross section due to resonance enhancement was also found for one of the diacetylene compounds in visible wavelength region.

1-(4′-Substituted phenyl)-4-(4′-methylpyridinium)butadiyne triflate (5ab), which was prepared by the reaction of 1-(4′-Substituted phenyl)-4-(4′-pyridyl) butadiyne (4ab) with methyl trifluoromethanesulfonate, was found to be grown into the large crystal due to the quaternized structure. The uv irradiation and thermal treatment of 5ab gave rise to 1,4-addition polymerization to yield the polydiacetylene. The third-order nonlinear optical susceptibility (χ (3)) of the polymer was determined by the Z-Scan method to exhibit the remarkable high value of 1.65×10−11esu at 650 nm.

CdSe microcryssals with various sizes was successfully embedded in SiO2 glass matrix by magnetron rf-sputtering technique. The mean size of microcrystals was controllable by changing the relative surface area ratio of the CdSe chips to the matrix in the target, and increased with increasing the relative area. The negative real part of the third-order optical susceptibility was seen for all of the present films, and the magnitude of the absolute value of real part increased with increasing concentration of CdSe. The imaginary part due to two photon absorption also increased with the CdSe concentration. After normalized with respect to the concentration, it was revealed that actual optical third-order nonlinearity of the CdSe microcrystals increased as the mean size decreased, in other words as the quantum confinement effect increased.

Polarized light-induced anisotropy of 4-dimethylamino-4′-nitroazobenzene (DMANA; NO2–C6H4–NN–C6H4–N(CH3)2) in PMMA is investigated by polarized spectroscopy and compared with the anisotropy of Disperse Orange 3 (DO3; NO2–C6H4–NN–C6H4–NH2) studied previously. The orientation factors evaluated from spectroscopic results show that the trans isomers of DMANA isomerize to cis forms by motion of the p-NO2–C6H4 group easily compared with motion of the p-N(CH3)2–C6H4 group. This result is different from the result of DO3 in PMMA where the trans forms tend to isomerize to cis forms by motion of the amino group side than that of nitro group side. We consider that this difference is due to the volume effect of the substituent at the para position of a phenyl group. This study clearly indicates that the motion of push–pull azo-dyes in the isomerization processes strongly depends on the relative volume of the p-substituent.

We report the behaviour of 3-(2-benzothiazolyl)-7-hexadecyloxycoumarin (HDBOC) mixed with stearic acid (SA) at the air—water interface. Detailed studies of the surface pressure vs. area per molecule isotherm measurements of mixed films of HDBOC and SA indicate the formation of organized aggregates. Miscibility studies reveal that distinct regions of mixing and demixing exist and are dependent on the molar composition and surface pressure exerted on the mixed film. Spectroscopic studies suggest that the HDBOC molecules are sandwiched between SA chains and form J aggregates. A comparative study of the spectroscopic properties in solution and in Langmuir—Blodgett films suggests differences in the molecular conformation of HDBOC in the two systems.

We have studied the spectroscopic properties of nile red (NR), a highly fluorescent laser dye, in organic solvents, binary solvent mixtures and polymers. Spectroscopic studies reveal remarkable changes in the absorption and emission band positions and intensities as a function of the polarity of the medium. Such large changes have been attributed to the twisted intramolecular charge transfer (TICT) state of the molecule in polar medium. Experimental results show that the molecule is sensitive to the polarity of its microenvironment and is an excellent probe for systems presenting restricted geometries. We have incorporated NR into thin films of poly (methyl methacrylate) (PMMA) and poly (vinyl alcohol) (PVA); it is found that the micropolarity in PVA is greater than that in PMMA; in PVA, the micropolarity corresponds to that of a binary mixture of acetonitrile and water, whereas in PMMA, the micropolarity corresponds closely to that of pure acetonitrile.

The two-photon absorption (TPA) of a bis(acridine) dimer (8) having singlet diradical character in its ground state was found to be enhanced by more than 2 orders of magnitude as compared to its closed-shell counterpart (12), which has the same structural backbone and atom composition. The dimer, a tetracation species consisting of two connected acridinium cation moieties with high coplanarity, was obtained during our attempts to synthesize triplet carbenes by double oxidation of an allenic precursor (3b). High conjugation over the two aromatic rings connected by dimerization was revealed by X-ray analysis, and a small HOMO-LUMO gap was found in the visible-near-infrared one-photon absorption spectrum in solution and in the crystalline state, exhibiting that the ground state of 8 has singlet diradical nature. Ab initio molecular orbital calculations of the ground state also suggested that 8 has an intermediate diradical character (y) of 0.685. Interconversion between diradical tetracation dimer 8 and closed-shell dication dimer 12 was achieved by oxidation/reduction in good yields and was accompanied by formation of monoradical trication dimer 13 as an intermediate. TPA measurements at near-infrared wavelengths revealed that diradical dimer 8 has large TPA cross sections (3600 GM at 1200 nm), while closed-shell 12 has TPA cross sections of21 GM. This result represents a straightforward comparison between the TPA activity of molecules with the same structural backbone and atom composition but with different degree of the diradical character, supporting the theoretical prediction that enhanced TPA intensity can be observed in the intermediate y region (0y1).

International audience; A great number of works have focused their research on the synthesis, design and optical properties of gold nanoparticles for potential biological applications (bioimaging, biosensing). For this kind of application, sharp gold nanostructures appear to exhibit the more interesting features since their surface plasmon bands are very sensitive to the surrounding medium. In this paper, a complete study of PEGylated gold nanostars and PEGylated bipyramidal-like nanostructures is presented. The nanoparticles are prepared in high yield and their surfaces are covered with a biocompatible polymer. The photophysical properties of gold bipyramids and nanostars, in suspension, are correlated with the optical response of single and isolated objects. The resulting spectra of isolated gold nanoparticles are subsequently correlated to their geometrical structure by transmission electron microscopy. Finally, the PEGylated gold nanoparticles were incubated with melanoma B16-F10 cells. Dark-field microscopy showed that the biocompatible gold nanoparticles were easily internalized and most of them localized within the cells.

The two-photon absorption properties of a self-organized dimer of a free-base and zinc(II) porphyrins tandem linked with an ethynylene group and terminated by imidazolyl and phenylethynyl groups were investigated. The self-organized dimer was found to exhibit strong two-photon absorption and furthermore the saturation of the two-photon absorption owing to the intense transition.

The mechanisms of photoinduced electron transfer in 1-aminopyrene (AP, D-H)-pyridine (Pyr, A) and -methylpyridine (MePyr, A) hydrogen-bonded complexes in nonpolar hexane solutions have been investigated by means of femtosecond-picosecond laser photolysis methods. Rapid electron transfer from the S 1 state of AP to the hydrogen-bonded Pyr or MePyr converging to the equilibrium state, (D * -H...A)⇄(D + -H...A - ), has been directly observed by time-resolved transient absorption spectral measurements

A phosphoniafluorene and a spirobiphosphoniafluorene bearing 4-(diethylamino)styryl groups were synthesized. These compounds exhibited bathochromically shifted absorption and emission, compared with their silicon analogues, because of the strong acceptor property of the phosphonium core. They also showed enhanced two-photon absorptions at around 930 nm.

Photoreduction processes of benzophenone (BP)-N,N-diethylaniline (DEA) system in acetonitrile solution were studied by means of femtosecond–pecosecond laser photolysis and time resolved transient absorption spectroscopy. The reaction processes including the formation of geminate ion pairs (IP) by electron transfer (ET) between BP* and DEA at encounter followed by intra-IP proton transfer giving the ketyl radical (BPH·) were clearly observed in both triplet and singlet excited state, while the IP produced by excitation of the CT complex between BP and amine formed easily in more or less concentrated solutions did not give BPH·. In addition to the detailed investigations on the BP-DEA system, we made comparative studies on BP–tertiary aromatic amine systems including N,N-diethyl-p-toluidine, N,N-dimethylaniline, and N-methyldiphenylamine. We observed clearly the characteristic tendency that the proton transfer rate in the 3IP decreased with decrease of the oxidation potential of the amine. This result was i...

Photoreduction processes of excited benzophenone (BP) by N,N-dimethylaniline (DMA) in acetonitrile solution were studied by means of picosecond-femtosecond laser photolysis and time resolved transient absorption spectroscopy as well as transient photoconductivity measurement. Proton transfer process in the triplet ion pair formed by electron transfer (ET) at encounter between 3BP* and DMA, competing with the ionic dissociation process was observed. It was clearly demonstrated that, in addition to the triplet ion pair, the ion pair produced by the excitation of the CT complex between BP and DMA formed in the ground state and that produced by ET reaction between 1BP* and DMA played important roles in the reaction processes of excited benzophenone. The behaviors of the three kinds of ion pairs were investigated in detail, leading to the elucidation of reaction mechanism of each ion pair. The reactivity characteristic of each kind of the ion pair and its relation to the structure of the ion pair were discussed.

A porphyrin-perinaphthothioindigo conjugate having two-photon absorption cross-sections of approximately 2000 GM and approximately 700 GM for trans- and cis-isomers, respectively, was synthesized and exhibited clear photochromic behavior upon one-photon and two-photon excitation.

International audience; Dipolar and symmetrical heptamethine dyes featuring strong linear absorption in the near-infrared spectral range (700−900 nm) were prepared at a gram scale. X-ray crystallographic structure of the dipolar chromophore is described revealing the remarkable planarity of the polyenic chain due to the central ring of the molecule. These chromophores present promising nonlinear absorption properties at telecommunication wavelengths (1400−1600 nm): (i) significant two-photon cross-sections were measured using the femtosecond Z-scan method, and (ii) their exceptional solubility allows us to carry out an optical-limiting experiment at 1500 nm in the nanosecond regime. In this regime, experimental data were interpreted on the basis of two-photon absorption (2PA) and 2PA-induced excited-state absorption (ESA). Finally, these systems, which present a lot of relevant properties (significant nonlinear absorption properties, two-step gram scale synthesis, high solubility, good thermal stability, and several sites of functionalization), open the way to numerous practical applications in biology, solid-state optical limiting, and signal processing.

A convenient synthesis of tetrabenzopentakisdehydro[12]annuleno[12]annulene 2c with substantial solubility was achieved by double cyclization of tetrabromotolan 3 with o-di-ethynylbenzene 4.

Phytochemical investigation of the 1-BuOH-soluble fraction of the MeOH extract of Alangium premnifolium resulted in the isolation of ten megastigmane glycosides, of which, two, (6R,9R)-3-oxo-alpha-ionol apiofuranosylglucopyranoside and roseoside with (6S,9R)-blumeol A as an aglycone were known. The structures of the eight new compounds were determined by spectroscopic methods.

Two-photon absorption (2PA) properties of self-assembled porphyrins were investigated. The butadiyne-linked porphyrin array exhibited a 20 times larger 2PA cross section than the meso-meso-linked self-assembled array due to the expansion of pi-conjugation. Higher-order nonlinear absorption was also observed in the former porphyrin.