High Two-photon Absorption Cross-sections Research Articles

One- and two-photon activated phototoxicity of conjugated porphyrin dimers with high two-photon absorption cross sections

Two-photon excited photodynamic therapy (PDT) has the potential to provide a highly targeted treatment for neoplastic diseases, as excitation can be pin-pointed to small volumes at the laser focus. In addition, two-photon PDT offers deeper penetration into mammalian tissue due to the longer wavelength of irradiation. Here we report the one-photon and two-photon excited PDT results for a collection of conjugated porphyrin dimers with high two-photon absorption cross sections. These dimers demonstrate high one-photon PDT efficacy against a human ovarian adenocarcinoma cell line (SK-OV-3) and exhibit no significant dark-toxicity at concentrations of up to 20 microM. Their one-photon excited PDT efficiencies, following irradiation at 657 nm, approach that of Visudyne, a drug used clinically for PDT. We investigated and optimised the effect of the photosensitizer concentration, incubation time and the light dose on the PDT efficacy of these dimers. These studies led to the selection of P2C2-NMeI as the most effective porphyrin dimer. We have demonstrated that P2C2-NMeI undergoes a two-photon activated process following excitation at 920 nm (3.6-6.8 mW, 300 fs, 90 MHz) and compared it to Visudyne. We conclude that the in vitro two-photon PDT efficacy of P2C2-NMeI is about twice that of Visudyne. This result highlights the potential of this series of porphyrin dimers for two-photon PDT.

Synthesis of hydrophilic conjugated porphyrin dimers for one-photon and two-photon photodynamic therapy at NIR wavelengths

We report the synthesis of a series of hydrophilic butadiyne-linked conjugated zinc porphyrin dimers, designed as photodynamic therapy (PDT) agents. These porphyrin dimers exhibit exceptionally high two-photon absorption cross sections (delta(max) approximately 8,000-17,000 GM) and red-shifted linear absorption spectra (lambda(max) approximately 700-800 nm) making them ideal candidates for one-photon and two-photon excited photodynamic therapy. Four polar triethyleneglycol substituents are positioned along the sides of each dimer, but, on their own, these TEG chains do not confer sufficient solubility in aqueous physiological media for reproducible delivery into live cells. Charged cationic (methylpyridinium and trimethylammonium) and anionic (sulfonate and carboxylate) substituents have been appended to the meso-positions of porphyrin dimers using three synthetic strategies: 1) Suzuki coupling, 2) Sonogashira coupling, and 3) nucleophilic Senge arylation. Approaches 1 and 3 both allow attachment of aromatic substituents directly to the meso-positions of porphyrins. Approach 2 provides a route to hydrophilic porphyrin dimers with an ethyne link between the porphyrin and the polar aromatic substituent. The palladium-catalysed approaches 1 and 2 allow the synthesis of a broader range of meso-capped porphyrins, as many aryl halides are available. However the synthesis of the intermediate required for these routes necessitates a statistical reaction step, which decreases the overall yield. On the other hand, Senge-arylation provides highly regioselective nucleophilic aromatic substitution, and offers higher overall yield than the other routes. All these charged dimers exhibit good solubility in polar solvents (e.g. methanol) and aqueous solvent mixtures (aqueous DMSO or DMF).

The theoretical simulation for two-photon absorption properties of novel A- π-D- π-A two-photon carbazole compounds

The optical properties of three newly synthesized A- π-D- π-A compounds have been studied by use of analytical response theory at the density functional theory level. The theoretical results show that there exist three charge-transfer states for each compound in the low energy regime. The trends for both oscillator strengths and excitation energies among the three compounds as predicted by the numerical simulations are highly consistent with those given by measurement. Large two-photon absorption cross sections are predicted for the three compounds. Furthermore, the solvent effect on the optical properties of the compounds is investigated. It is found that the excitation energies in solvent DMF show a red-shift compared to those in gas case, and the two-photon absorption cross sections are highly enhanced. The optical properties of the compounds with experimental geometric parameters are also investigated. The oscillator strengths are found to be smaller due to the bent molecular structures. The calculated results predict that much higher two-photon absorption cross sections would be observed when a laser with a shorter wavelength is applied.

Acetylene-Substituted Two-Photon Absorbing Molecules With Rigid Elongated Pi-Conjugation: Synthesis, Spectroscopic Properties and Two-Photon Fluorescence Cell Imaging Applications

Two asymmetrical molecules with substituted acetylene as central rigid elongated conjugation are reported as potential chromophores for two-photon microscopic imaging. These molecules consist of a typical D-pi-A structure, have different donors (D), the same pi-conjugated center (pi) and the same acceptor (A). Structural characterization and spectroscopic properties, including single-photon (linear) absorption, quantum yields, single-photon fluorescence, and two-photon absorption spectra, were studied in solvents with different polarity. These acetylene-substituted molecules were found to have high two-photon absorption cross-sections (for example, 690 GM for molecule 1 in toluene), which were determined by a two-photon induced fluorescence method using a femtosecond Ti: sapphire laser as excitation source. Single- and two-photon cellular imaging experiments demonstrate that the substituted acetylene derivatives could be one kind of promising two-photon fluorescence probes for cellular imaging.

Zinc(II)- and Copper(I)-Mediated Large Two-Photon Absorption Cross Sections in a Bis-cinnamaldiminato Schiff Base

A Schiff base ligand has been synthesized by condensing 1,2-diaminobenzene with 4-(dimethylamino)cinnamaldehyde to give a donor-pi-acceptor-pi-donor system which does not show any two-photon absorption cross section but which does, upon complexation with Zn(II) or Cu(I), exhibit very high two-photon absorption cross sections.

Synthesis of Two-Photon Absorbing Unsymmetrical Branched Chromophores through Direct Tris(bromomethylation) of Fluorene

Branched fluorene-based chromophores bearing electron-donating diphenylamino or electron-withdrawing nitro groups were synthesized as well as their linear analogues. An efficient synthetic method was developed via a novel 2,4,7-tris(bromomethyl)-9,9-diethylfluorene intermediate. The bromomethyl groups in this key intermediate were converted to either phosphonate or carboxaldehyde moieties, facilitating preparation of a high functionality branched structure. It was found that the reactivity at position 4 is attenuated in the bromomethyl and phosphorylated derivates, facilitating the selective and systematic functionalization of the fluorenyl system. All compounds were stable up to ca. 350 degrees C, except for a sterically crowded branched derivative. The linear optical properties of the compounds were investigated by UV-visible, steady-state fluorescence, and excitation anisotropy spectroscopic measurements. Fluorescence quantum yields were greater than or equal to 0.84 for symmetric linear and unsymmetric branched derivatives. Very high two-photon absorption (2PA) cross-sections were achieved (5765 GM at 520 nm and 4194 GM at 570 nm), as determined with use of picosecond and femtosecond laser excitation sources, respectively.

Fabrication of Nano‐Precision PDMS Replica Using Two‐Photon Photopolymerization and Vacuum Pressure Difference Technique.

AbstractFor Abstract see ChemInform Abstract in Full Text.

TWO-PHOTON ABSORPTION AND FLUORESCENCE WITH QUADRUPOLAR AND BRANCHED CHROMOPHORES—EFFECT OF STRUCTURE AND BRANCHING

The photophysical and two-photon absorption (TPA) properties of three homologous quadrupolar and one related three-branched chromophores were investigated. Design of the quadrupoles is based on the symmetrical functionalization of a biphenyl core. Modulation of the nonlinear absorptivity/transparency/photostability trade-off can be achieved by playing with the twist angle of the core and on the spacers (phenylene-vinylene versus phenylene-ethynylene). The quadrupolar chromophores combine high TPA cross-sections, high fluorescence quantum yield and solvent sensitive photoluminescence properties. The branched structure exhibits spectrally broadened TPA in the NIR region (up to 3660 GM at 740 nm measured in the femtosecond regime) but reduced sensitivity to the environment.

Fabrication of Nano-precision PDMS Replica Using Two-photon Photopolymerization and Vacuum Pressure Difference Technique

It is undoubtingly believed that a revolution in miniaturization, in the field of microelectromechanical systems (MEMS), nano- and biotechnology etc., is under way. Multidimensional micro structures are fabricated by mainly two methods, such as laser rapid prototyping and lithography. Since it is a process that builds features layer by layer, rapid prototyping is a very slow process and is difficult to fabricate smaller objects. 1 On the other hand, the conventional lithographic technique requires an etching process that limits to build complicated figures. Recently, two-photon photopolymerization has attracted increasing attention as an innovative tool for micro- and nanofabrication due to its intrinsic multi-dimensional fabrication capability and subdiffraction limited spatial resolution. 2,3 Two-photon absorption probability strongly depends quadratically on excitation beam intensity confining the process at the vicinity of the focus. Thus, by using two-photon excitation one can activate chemical and physical processes only for a tightly focused spot in the bulk medium with high spatial resolution. This substantial increase in structural complexity was only possible by using chromophores with high two-photon absorption cross-sections (σ ). It is apparent that the synthesis of chromophores with even larger two-photon activity will unleash improvements in the capability and performance of a variety of two-photon absorption application including multi-dimensional nano- and microfabrication. In this paper, we describe the synthesis of newly designed highly efficient two-photon chromophore and fabrication of three-dimensional nano-precision PDMS replica using vacuum pressure difference technique (VPDT) and twophoton photopolymerization. The two-photon absorbing chromophore 3 with long alkyl chain for improved solubility was synthesized using palladium catalyzed coupling reaction designed by Heck 4 from compound 1 and 2. The compound 1 was obtained from Vilsmeier-Haack fomylation of triphenylamine followed by Wittig raction, and the 2,7dibromofluorene was reacted with excess amount of ethylhexylbromide to give compound 2. The resulting twophoton chromophore 3 was extensively purified before use as a light sensitizer/photoinitiator in two-photon photopolymerization. 5 The optical transparency of a chromophore at the wavelength of operation is crucial for successful 3D microfabrication with two-photonpolymerzation. As shown in steady-state absorption and emission spectra (Figure 1), the two-photon chromophore 3 has no absorption beyond 475 nm making itself ideal for two-photon application at the wavelength of 780 nm which is wavelength of our interest. Two-photon absorption cross-section of chromophore 3 at 780 nm was found to be σ = 4.7 × 10 −48 cm 4 s/photon with

Synthesis and Two‐Photon Absorption of Highly Soluble Three‐Branched Fluorenylene‐vinylene Derivatives.

Two new three-branched fluorenylene-vinylene derivatives were synthesized by triple Heck-type or Horner–Wadsworth–Emmons reactions. Their one-photon absorption and fluorescence as well as their two-photon absorption properties are reported. These compounds, which combine very high solubility in organic solvents, high fluorescence quantum yield and giant two-photon absorption cross-sections in the red-NIR region (up to 3660 GM, in the femtosecond regime) are promising candidates for both optical power limiting applications and two-photon laser scanning microscopy.

Synthesis and two-photon absorption of highly soluble three-branched fluorenylene-vinylene derivatives

Two new three-branched fluorenylene-vinylene derivatives were synthesized by triple Heck-type or Horner–Wadsworth–Emmons reactions. Their one-photon absorption and fluorescence as well as their two-photon absorption properties are reported. These compounds, which combine very high solubility in organic solvents, high fluorescence quantum yield and giant two-photon absorption cross-sections in the red-NIR region (up to 3660 GM, in the femtosecond regime) are promising candidates for both optical power limiting applications and two-photon laser scanning microscopy.

Synthesis and two-photon absorption of triphenylbenzene-cored dendritic chromophores

The synthesis and the characterization of triphenylbenzene-cored dendrimers of first- and second-generation are described. Their absorption, photoluminescence as well as their two-photon absorption properties have been investigated and compared to a quadrupolar counterpart. These molecules combine wide transparency in the visible range and high two-photon absorption cross-sections that increase with the generation, making these dendrimers promising systems for optical power limiting applications.

Study of Two-Photon Absorption Spectral Property of a Novel Nonlinear Optical Chromophore Using Femtosecond Continuum

The degenerate two-photon absorption (TPA) spectrum has been studied for a novel organic chromophore (AF389) that exhibits extremely high TPA cross-section values around the ∼800 nm range in both nanosecond and femtosecond domains. To measure the direct degenerate TPA spectrum of AF389 in the femtosecond regime, we have developed a new technique that is based on the use of a single continuum-generation beam as an intense coherent white-light source for TPA excitation. The different spectral components of the input continuum beam are spatially dispersed and then pass the sample through different pathways so that nondegenerate TPA processes among different spectral components can be avoided. Our results show that the TPA spectrum of AF389 is different from the linear absorption spectrum on the scale of absorbing photon energy. There is a significant blue shift of the absorption peak position for the TPA spectrum with respect to the linear absorption spectrum, indicating that the transition pathways are different for the TPA and linear absorption processes.

New technique for degenerate two-photon absorption spectral measurements using femtosecond continuum generation

We present a new technique for direct measurements of degenerate two-photon absorption (TPA) spectra of two-photon absorbing materials including non-fluorescent samples. This technique is based on the use of an intense single continuum-generation beam as the coherent whitelight source with specially flattened spectral distribution. The different spectral components of the continuum beam are spatially dispersed and then passed through the sample material along different pathways so that nondegenerate TPA processes among different input spectral components can be avoided. By comparing the input and transmitted continuum spectral distributions, the TPA spectrum for a given sample can be obtained. As an example, the continuous TPA spectrum (from 550 to 1000 nm) is measured for a novel two-photon-absorbing compound (AF-389) which exhibits an extremely high TPA cross-section value of ~1x10-20 cm4/GW, or ~249 GM, around ~800-nm spectral range in femtosecond regime.

Optimization of quadrupolar chromophores for molecular two-photon absorption

Multiphoton absorption is attracting considerable attention owing to applications in various fields including optical power limitation, and high resolution imaging of biological tissues. Within this framework, our aim has been the design of optimized NLO-phores with very high two-photon absorption (TPA) cross-sections in the visible and/or NIR region and high fluorescence quantum yield. Our strategy was based on the push–push or pull–pull functionalization of rigid conjugated cores built from a rigidified biphenyl or bithiophene moiety. A series of push–push and pull–pull elongated chromophores have been prepared and their nonlinear absorption properties investigated by determining their two-photon excited fluorescence (TPEF) characteristics. The TPA spectra of theses derivatives can be tuned and their TPA responses boosted by playing on the nature of the rigid core and electroactive end groups. As a result, quadrupolar molecules showing very large TPA cross-sections (up to 1.3×10 −47 cm 4 s photon −1 ) in the visible red and/or NIR region have been obtained. Such derivatives are promising for optical limitation applications as well as for TPEF imaging of cellular membranes.

Photoluminescence studies and read/write process of a strong two-photon absorbing chromophore

The optical properties of a fluorene-based chromophore exhibiting a high two-photon absorption cross section have been investigated both in the pure state and as a guest–host system in poly(N-vinylcarbazole). Upon irradiation with a helium cadmium (He–Cd) laser at 325 nm, the guest–host sample exhibits a blueshift with a maximum emission at 459 nm. Information written onto the samples in the blue can also be read using an Ar+ laser. The chromophore undergoes a chemical change upon irradiation in air, and has been found to no longer exhibit upconversion after this transformation. Infrared analysis of the sample (the chromophore) before and after irradiation was carried out, and the spectra suggest the formation of a new conjugated species. Other applications we have developed using this phenomenon include the successful writing of optical device structures in polymer films where the AF-50 is a guest material.

Propriétés de limitation optique du 1-(P-N,N-dimethylamino)-4-(P-cyanophenyl)-1,3-butadiene

The optical-limiting behavior of 1-(p-N,N-dimethylamino)-4-(p-cyanophenyl)-1,3-butadiene (DCB) solution was experimentally and theoretically studied at 532 nm with nanosecond and picosecond pulses. The transmissivity measurements were fitted using a three-level molecular model including two-photon absorption. The best fits were obtained with very high two-photon absorption cross-sections, indicating that two-photon absorption is the predominant mechanism of the strong optical limiting behavior [2,3].

Optical-limiting properties of a push–pull diphenyl-butadiene

The optical-limiting behavior of 1-( p- N, N-dimethylamino)-4-( p-cyanophenyl)-1,3-butadiene (DCB) solution in dichloromethane was experimentally and theoretically studied at 532 nm with nanosecond and picosecond pulses. Energy-dependent transmissivity measurements were fitted using a three-level molecular model including two-photon absorption. The best fits were obtained with very high two-photon absorption cross-sections, indicating that two-photon absorption is the predominant mechanism of the strong optical limiting behavior observed in a DCB solution.