Maximum Two-photon Absorption Cross-section Research Articles

Amplified Two-Photon Absorption inTrans-A2B2-Porphyrins Bearing Nitrophenylethynyl Substituents

We show that peripheral nitro groups enhance the maximum two-photon absorption cross-section of trans-A(2)B(2)-porphyrins bearing two phenylethynyl substituents by more than one order of magnitude. Maximum values as high as 1000 GM result from realization of suitable conditions for effective resonance enhancement along with a lowering of the energy and intensification of the two-photon allowed transitions in the Soret region.

Influence of rotational isomerism on two-photon absorption properties of FTC chromophores

The influence of rotational isomerism on the two-photon absorption (TPA) of FTC chromophores has been investigated using the quadratic response theory with the B3LYP functional. Eight rotamers induced by three rotatable single bonds in the molecule are fully optimized, and it is found that their conformational energies are nearly degenerate. Our calculations demonstrate that rotational isomerism has an important effect on the TPA cross sections. For a certain rotamer, the maximum TPA cross section is enhanced significantly. In addition, in the longer wavelength region, the rotational isomerism could lead to a large shift of the TPA position.

Synthesis and two-photon absorption properties of a red-emitting poly(2,6-anthracenevinylene) derivative with donor–acceptor–donor motif

A novel poly(2,6-anthracenevinylene) derivative (Pr) with donor–acceptor–donor motif was synthesized by Witting reaction of 9,10-dicyano-2,6-bis(diethylphosphoryl-methyl)anthracene and 4,6-bis(bis(2-ethylhexyl)amino)isophthalaldehyde, and its one- and two-photon properties were investigated. Pr showed a number-average molecular weight of 11,360 by end-group analysis and 15,300 by GPC, respectively. The Pr solution in toluene exhibited a maximal absorption wavelength peaked at 591nm with the onset wavelength of 690nm and emitted a red fluorescence centered at 665nm with a fluorescence quantum yield of 0.10. Pr exhibited the maximum two-photon absorption cross-section of 1430g per repeating unit at 920nm measured by two-photon-induced fluorescence method. The results indicate the polymers with large TPA cross sections can be obtained by employing effective TPA chromophores as the building blocks, and the wavelength of the maximal TPA for 2,6-anthracenevinylene-based polymers could be tuned by attaching appropriate donor and/or acceptor substituents.

Dipolar versus Octupolar Triphenylamine‐Based Fluorescent Organic Nanoparticles as Brilliant One‐ and Two‐Photon Emitters for (Bio)imaging

Two related triphenylamine-based dipolar and octupolar fluorophores are used to prepare aqueous suspensions of fluorescent organic nanoparticles (FONs) via the reprecipitation method. The obtained spherical nanoparticles (30-40 nm in diameter) are fluorescent in aqueous solution (up to 15% fluorescence quantum yield) and exhibit extremely high one- and two-photon brightness, superior to those obtained for quantum dots. Despite the two chromophores showing similar fluorescence in solution, the fluorescence of FONs made from the octupolar derivative is significantly red-shifted compared to that generated by the dipolar FONs. In addition, the maximum two-photon absorption cross section of the FONs made from the octupolar derivative is 55% larger than that of the dipolar derivative FONs. The experimental observations provide evidence that the different molecular shape (rodlike versus three-branched) and charge distribution (dipolar versus octupolar) of the two chromophores strongly affect the packing inside the nanoparticles as well as their spectroscopic properties and colloidal stability in pure water. The use of these FONs as probes for biphotonic in-vivo imaging is investigated on Xenopus laevis tadpoles to test their utilization for angiography. When using FONs made from the octupolar dye, the formation of microagglomerates (2-5 μm scale) is observed in vivo, with subsequent lethal occlusion of the blood vessels. Conversely, the nanoparticles of the dipolar dye allow acute imaging of blood vessels thanks to their suitable size and brightness, while no toxic effect is observed. Such a goal cannot be achieved with the dissolved dye, which permeates the vessel walls.

Benzothiazoles with Tunable Electron-Withdrawing Strength and Reverse Polarity: A Route to Triphenylamine-Based Chromophores with Enhanced Two-Photon Absorption

A series of dipolar and octupolar triphenylamine-derived dyes containing a benzothiazole positioned in the matched or mismatched fashion have been designed and synthesized via palladium-catalyzed Sonogashira cross-coupling reactions. Linear and nonlinear optical properties of the designed molecules were tuned by an additional electron-withdrawing group (EWG) and by changing the relative positions of the donor and acceptor substituents on the heterocyclic ring. This allowed us to examine the effect of positional isomerism and extend the structure-property relationships useful in the engineering of novel heteroaromatic-based systems with enhanced two-photon absorption (TPA). The TPA cross-sections (δ(TPA)) in the target compounds dramatically increased with the branching of the triphenylamine core and with the strength of the auxiliary acceptor. In addition, a change from the commonly used polarity in push-pull benzothiazoles to a reverse one has been revealed as a particularly useful strategy (regioisomeric control) for enhancing TPA cross-sections and shifting the absorption and emission maxima to longer wavelengths. The maximum TPA cross-sections of the star-shaped three-branched triphenylamines are ∼500-2300 GM in the near-infrared region (740-810 nm); thereby the molecular weight normalized δ(TPA)/MW values of the best performing dyes within the series (2.0-2.4 GM·g(-1)·mol) are comparable to those of the most efficient TPA chromophores reported to date. The large TPA cross-sections combined with high emission quantum yields and large Stokes shifts make these compounds excellent candidates for various TPA applications, including two-photon fluorescence microscopy.

The synthesis of tetrahedral bipyridyl metallo-octupoles with large second- and third-order nonlinear optical properties

Two new 4,4′-bis(donor)-6,6′-diphenyl- 2,2′-bipyridine ligands and their corresponding D 2d (Cu I, Ag I, Zn II) octupolar metal complexes were synthesized, and their linear and nonlinear optical properties were investigated. A single crystal X-ray structure was also determined for the bis[4,4′-bis(diethylaminostyryl)-6,6′-diphenyl-bipyridine]copper(I) complex, which revealed a distorded pseudo-tetrahedral geometry. Molecular second-order nonlinear optical properties were determined for the complexes using the Harmonic Light Scatterring technique at 1.91 μm. These metallo-chromophores display large first hyperpolarizabilities β 1.91 in the range of 211–340 × 10 −30 esu, which increase with the Lewis acidity of the metal ion. The two-photon absorption properties of the bipyridyl ligands and related complexes were determined using either the two-photon emission method for fluorescent compounds or the open aperture Z-scan technique for non emissive ones. The complexes display red-shifted two-photon absorption bands compared to their metal-ion free chromophores, as well as a large increase of the maximum two-photon absorption cross-sections.

A comparative study of one- and two-photon absorption properties of pyrene and perylene diimide derivatives

Two important classes of organic molecules, perylene diimide (PDI) and pyrene derivatives have been found to possess relatively excellent photophysical and photochemical properties and especially high two-photon absorption cross sections (δ(T)(max)). Herein, one-photon absorption (OPA) and two-photon absorption (TPA) properties of some novel PDI and pyrene derivatives were comparatively investigated by the density functional theory (DFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods. The calculated results indicate that with respect to PDI derivatives, the maximum TPA cross-sections for pyrene compounds increase obviously, the maximum peaks of OPA and TPA spectra are blue-shifted, the ΔE(H-L) (energy gaps between the highest occupied orbital and the lowest unoccupied orbital) increase. The different π-conjugated bridges (fluorene and pyrene) and terminal groups have slight effect on the OPA properties. Nevertheless, the molecules bearing 1,6-disubstituted pyrene as the π-conjugated bridge display the largest δ(T)(max) in both series of compounds 3 and 4. Moreover, the δ(T)(max) values of molecules with benzothiazole-substituted terminal groups are larger than those of the molecules with diphenylamine, which is attributed to benzothiazole groups stabilizing the planarity of the branch parts, extending the conjugated length and increasing the π-electron delocalized extent. Furthermore, the molecular size has marked effect on OPA and TPA properties. It is worthy to mention that cruciform 8 displays the largest δ(T)(max) among all the studied molecules in the range of 600-1100 nm. This research could provide a better understanding for the origin of the linear and nonlinear optical properties, and it would be helpful to gain more information about designing two-photon absorption materials with large δ(T)(max).

Neutral push-pull chromophores for nonlinear optical imaging of cell membranes

A new class of push-pull molecules was recently identified, based on pyridine dicarboxamide as an electron acceptor group and bearing a fluorenethynyl pi-conjugated bridge. The molecules present good second and third order nonlinear properties, with a static quadratic hyperpolarisability mubeta (at 1.907 microm) of 320 x 10(-48) esu (mubeta(0) = 249 x 10(-48) esu) and a maximum two-photon absorption cross-section of 1146 GM. Starting from this generic structure, we designed a series of eight amphiphilic nonlinear probes, varying the length of the lipophilic tail and the nature of the polar head, and tested their cell membrane affinity by nonlinear optical imaging. A good membrane affinity was observed with probes bearing short alkyl chains and carbohydrate moieties as the polar head, emphasizing the importance of the lipophilic-hydrophilic balance, as well as the role of the polar head. This original approach based on carbohydrate head groups is an important advancement in the design of membrane probes, since these highly versatile functional groups confer adequate hydrophilicity and yet conserve overall molecular neutrality.

Theoretical studies of one- and two-photon absorption properties for three molecules with different centers (B and N) and peripheral substituted groups [N(CH 3) 2 and CN

Three molecules with different centers (boron and nitrogen) and peripheral substituted groups [N(CH 3) 2 and CN] have been theoretically studied with B3LYP/6-31G(d) associated with ZINDO and sum-over-states methods. The maximum two-photon absorption cross-section δ max of the molecule with boron (B) center and N(CH 3) 2 peripheral group is larger than that of the molecule with nitrogen (N) center and N(CH 3) 2 peripheral group. As for the two molecules with N center, the δ max is obviously increased with the change from N(CH 3) 2 to CN group. This indicates that the large intramolecular charge transfer is in favor of the TPA response.

Theoretical study on two-photon absorption properties of novel multi-branched compounds

We have studied the one-photon absorption （OPA） and two-photon absorption （TPA） properties of the one-, two- and three-dimensional compounds with the same unit of （4-{2-［4-（2-pyridin-4-yl-vinyl）-phenyl］-vinyl}-phenyl）-amine moieties, using the response theory approach at the hybrid density functional theory level. The numerical simulation shows that the three organic molecules exhibit strong OPA and TPA capabilities. All chromophores present two linear absorption peaks in the ultra UV-visible region, which is in agreement with the experimental measurements. Strong broadband TPA properties from 780 to 1020 nm have been demonstrated in the near infrared region. The ratio of the largest TPA cross sections for three molecules DPVPA, BPVPA and TPVPA is 1.0∶2.3∶4.0, and the molecule TPVPA has the maximum TPA cross section 101.73×10-48 cm4·s. It is substantiated that the TPA cross section can be effectively enhanced with increasing molecular dimensionality. The charge-transfer process for the charge-transfer state is visualized in order to understand the enhancement of the TPA cross sections.

Two-Photon Absorption Properties of Two Kinds of Compounds with Fluorene as Centre

The two-photon absorption properties of two newly synthesized compounds containing fluorene as a π centre(denoted SK-G1 and NT-G1) were calculated using a response function method with density functional theory.Results show that both compounds have large one-photon and two-photon absorption abilities.In the low energy region,the maximum one-photon absorption strength of NT-G1 is twice as much as that of SK-G1 and its maximum absorption is red shifted compared to that for SK-G1.The maximum two-photon absorption cross section of NT-G1 is about five times as large as that of SK-G1 and those are found for the second excited states.Furthermore,NT-G1 has a wider two-photon absorption energy band.The optical properties of the molecules are closely related to their charge transfer processes when they are excited.The solvent effect on their one-photon absorption properties was calculated using the Onsager model.The numerical calculation is found to be in good agreement with experimental measurements.

新型双光子吸收生色分子的电化学、热性能和光物理性质

Electrochemical, thermal, and photophysical properties of novel two- (BPODPA), four- (BBPOPA), and six-branch (TBPOA) triphenylamine chromophores are studied. The decomposition temperature of chromophores reaches 373-412 C. The electrochemical properties is explored by cyclic voltammetry. The ionization potential of chromophores is in the range of 5.14-5.18 eV. Excitation at 400 nm reveals emission peaks at 483-487 nm and the fluorescence quantum yields are 0.73-0.75 in CH2Cl2 Two-photon absorption (TPA) properties of chromophores are measured by nonlinear transmission method. The maximum TPA cross-section values are measured at 758 nm to be 20369 GM (1 GM=10^{-50} cm4s/photon) for TBPOA, 7024 GM for BBPOPA, and 1227 GM for BPODPA, respectively. When pumped with 800-nm laser irradiation, chromophores show strong two-photon excited blue-green fluorescence at 502-518 nm. These results provide a basis for understanding the electronic and optical properties of the conjugated multi-branch chromophore in terms of the underlying molecular and electronic structures.

Theoretical study of the one- and two-photon absorption properties of two series of fluorene derivatives

A dipolar molecule and two series of fluorene derivatives have been theoretically studied with B3LYP/6-31G(d) associated with ZINDO–SOS method. The different peripheral groups and lengthening the bridge have effect on the one-photon absorption. The maximum two-photon absorption cross sections δmax for the fluorene derivative (1B) is more than three times as that of the dipolar counterpart (S1). The δmax are obviously increased as the conjugation length increases from the series 1 molecules to the series 2 counterparts. Meanwhile, the δmax are increased with the stronger electron-donating (accepting) capability.

Novel benzylidene cyclopentanone dyes for two-photon photopolymerization

Two novel benzylidene cyclopentanone dyes ( 1 and 2) containing coumarin moiety were synthesized. Their photophysical properties were investigated using UV–vis spectra, fluorescence spectra and two-photon excited spectra. The maximum two-photon absorption cross-sections ( δ max) of two compounds were determined as 939 GM and 1150 GM, respectively, with femtosecond laser pulses. Combined with commercial photoinitiator 4,4′-dimethyl-diphenyliodinium hexafluorophosphate (Omnicat 820), both of two dyes exhibited higher sensitizing photopolymerization efficiency than the common used high-efficient photosensitizer 2,5-bis-[4-(dimethylamino)-benzylidene]-cyclopentanone in one-photon photopolymerization experiments. Using 2 as sensitizer or initiator directly, 2D and 3D nanopatterns were successfully fabricated by two-photon initiated polymerization.

A two-photon absorption study of fluorene and carbazole derivatives. The role of the central core and the solvent polarity

The two-photon absorption (TPA) properties of a series of symmetrical fluorene and carbazole derivatives have been studied to determine the role of the central core and the solvent polarity. The molecules bear triphenylamine, oxadiazole and pyrene as electron donating, electron acceptor and π-conjugated edge substituents, respectively. Triphenylamine and pyrene substituents with fluorene-core as well as oxadiazole substituent with carbazole-core constitute the optimum selections for enhanced TPA properties. Studying the effect of the solvent polarity it is shown that maximum TPA cross-sections (as high as 1024 GM) are achieved in a solvent of intermediate polarity.

Theoretical Study of One- and Two-Photon Absorption Properties of Octupolar D2d and D3 Bipyridyl Metal Complexes

The molecular equilibrium structures, electronic structures, and one- and two-photon absorption (TPA) properties of C2v (Zn(II), Fe(II) and Cu(I)) dipolar and D2d (Zn(II) and Cu(I)) and D3 (Zn(II)) octupolar metal complexes featuring different functionalized bipyridyl ligands have been studied by the ZINDO-SOS method. The calculated results show that one- and two-photon absorption properties of metal complexes are strongly influenced by the nature of the ligands (donor end groups and pi linkers) and metal ions as well as by the symmetry of the complexes. The length of the pi-conjugated backbone, the Lewis acidity of the metal ions, and the increase of ligand-to-metal ratio result in a substantial enhancement of the TPA cross sections of metal complexes. Substitution of C=N and N=N for C=C plays an important role in altering the maximum TPA wavelengths and the maximum TPA cross sections of metal complexes. Of them, the C=N substituted metal complexes have relatively large TPA cross sections. Replacing styryl with thienylvinyl makes the one-photon absorption wavelength red shift and at the same time leads to a great decrease of the maximum TPA cross sections of metal complexes. The possible reason is discussed. In the range 500-1250 nm, octupolar metal complexes exhibit intense TPAs and therefore are promising candidates for TPA materials.

A comparative study of one- and two-photon absorption properties of meso– meso singly, meso-β doubly and meso– meso β–β β–β triply linked Zn II-porphyrin oligomers

The electronic structures, one-photon absorption (OPA) and two-photon absorption (TPA) properties of the meso– meso singly, the meso-β doubly and the meso– meso β–β β–β triply linked Zn II-porphyrin dimers and trimers have been comparatively studied by using the hybrid B3LYP functional combined with the 6-31G basis set and ZINDO-SOS methods. The results show that on going from the dimers to the trimers, due to the increased conjugation chain, the maximum TPA positions are red-shifted and the maximum TPA cross sections produce a remarkable enhancement. The calculated maximum TPA cross sections of the studied molecules are in the range of 25.4–616.3 × 10 −48 cm 4 s/photon. Compared with the meso– meso singly linked Zn II-porphyrin derivatives, the meso-β doubly and the meso– meso β–β β–β triply linked Zn II-porphyrin derivatives have larger TPA cross sections at 700–1000 nm. They are promising candidates for TPA materials.

Theoretical study of one- and two-photon absorption properties of olefin-linked paracyclophane oligomers

The electronic structures and the one- and two-photon absorption (TPA) properties of two series of the olefin-linked paracyclophane (pCp) oligomers have been studied using AM1 and ZINDO-SOS methods. The relationship between the TPA cross sections and the molecular chain length is obtained. The maximum TPA cross section increases in proportion to Nα (N denotes the number of repeat units) and the values of α depend on different molecular structures. The olefin-linked pCp oligomers, which have good transparency and large TPA cross sections, are promising candidates for TPA materials.Key words: two-photon properties, paracyclophane oligomer, AM1, ZINDO-SOS.

Fluorescence upconversion properties of a class of improved pyridinium dyes induced by two-photon absorption

We report the fluorescence upconversion properties of a class of improved pyridinium toluene- p-sulfonates having donor– π–acceptor (D– π–A) structure under two-photon excitation at 1064 nm. The experimental results show that both the two-photon excited (TPE) fluorescence lifetime and the two-photon pumped (TPP) energy upconversion efficiency were increased with the enhancement of electron-donating capability of the donor in the molecule. It is also indicated that an overlong alkyl group tends to result in a weakened molecular conjugation, leading to a decreased two-photon absorption (TPA) cross section. By choosing the donor, we can obtain a longest fluorescence lifetime of 837 ps, a highest energy upconversion efficiency of ∼6.1%, and a maximum TPA cross-section of 8.74×10 −48 cm 4 s/photon in these dyes.

Theoretical investigation on the one- and two-photon absorption properties of a series of porphyrazines with annulated 1,2,5-thiadiazole and 1,4-dimethyloxybenzene moieties

On the basis of equilibrium geometries optimized by B3LYP/6-31G(d) method, the one-photon absorption properties of a series of substituted porphyrazines have been investigated theoretically using time-dependent density functional theory and the semiempirical ZINDO method, respectively. The comparisons with the available experimental data confirmed that the reliability of the ZINDO method in predicting the electronic absorption properties. According to the one-photon absorption properties obtained from the ZINDO method, two-photon absorption properties of molecules have been studied, using ZINDO and sum-over-states methods. The results have showed that the molecule with symmetrically substituted with electron donors exhibits the maximum two-photon absorption cross-section (up to 5276.8 GM) in all the studied molecules. The molecular centrosymmetry has a positive effect on the enhancement of the two-photon absorption cross-section. For the molecules with multi two-photon absorption peaks, the cross-section in the region from 750 to 860 nm is enhanced by one order of magnitude compared with that in the region from 1050 to 1200 nm.