Maximum Two-photon Absorption Research Articles

Theoretical studies of one- and two-photon absorption properties for two series of three-branched fluorenylene–vinylene compounds with different centers (B, N) and peripheral substituted groups

Two series of three-branched fluorenylene–vinylene compounds with different centers (B, N) and peripheral substituted groups were investigated. The equilibrium geometries and electronic structures were obtained by using the density functional theory B3LYP and 6-31G basis set. The one- and two-photon absorption properties of all the molecules were studied theoretically with a ZINDO–SOS method in detail. It can be seen that the maximum one-photon absorption (OPA) intensities and the maximum two-photon absorption (TPA) cross sections values δ max are gradually increased with the stronger electron-donating capability [H < OH < N(CH 3) 2] or electron-accepting one (H < CHO < NO 2). This indicates that intramolecular charge transfer from the center to the peripheral substituted groups (or vice versa) plays a very important role on the TPA.

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.

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 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 in TeO2-PbO glasses excited at 532 and 590 nm

Degenerate two-photon absorption (TPA) in a binary glass with composition TeO2-PbO is reported. The TPA coefficient, α2, obtained with nanosecond laser pulses at 532 and 590 nm, increases when the relative amount of PbO is increased. The maximum TPA coefficient, α2= 12.6 cm/GW, is comparable to or larger than the values reported for crystalline semiconductors and other recently reported glasses.

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.

Two-Photon Transitions in Quadrupolar and Branched Chromophores: Experiment and Theory

A combined experimental and theoretical study is conducted on a series of model compounds in order to assess the combined role of branching and charge symmetry on absorption, photoluminescence, and two-photon absorption (TPA) properties. The main issue of this study is to examine how branching of quadrupolar chomophores can lead to different consequences as compared to branching of dipolar chromophores. Hence, three structurally related pi-conjugated quadrupolar chromophores symmetrically substituted with donor end groups and one branched structure built from the assembly of three quadrupolar branches via a common donor moiety are used as model compounds. Their photophysical properties are studied using UV-vis spectroscopy, and the TPA spectra are determined through two-photon excited fluorescence experiments using femtosecond pulses in the 500-1000 nm range. Experimental studies are complemented by theoretical calculations. The applied theoretical methodology is based on time-dependent density functional theory, the Frenkel exciton model, and analysis in terms of the natural transition orbitals of relevant electronic states. Theory reveals that a symmetrical intramolecular charge transfer from the terminal donating groups to the middle of the molecule takes place in all quadrupolar chromophores upon photoexcitation. In contrast, branching via a central electron-donating triphenylamine moiety breaks the quadrupolar symmetry of the branches. Consequently, all Frank-Condon excited states have significant asymmetric multidimensional charge-transfer character upon excitation. Subsequent vibrational relaxation of the branched chromophore in the excited state leads to a localization of the excitation and fluorescence stemming from a single branch. As opposed to what was earlier observed when dipolar chromophores are branched via the same common electron-donating moiety, we find only a slight enhancement of the maximum TPA response of the branched compound with respect to an additive contribution of its quadrupolar branches. In contrast, substantial modifications of the spectral shape are observed. This is attributed to the subtle interplay of interbranch electronic coupling and asymmetry caused by branching.

Platinum Acetylide Two-Photon Chromophores

To explore the photophysics of platinum acetylide chromophores with strong two-photon absorption cross-sections, we have investigated the synthesis and spectroscopic characterization of a series of platinum acetylide complexes that feature highly pi-conjugated ligands substituted with pi-donor or -acceptor moieties. The molecules (numbered 1-4) considered in the present work are analogs of bis(phenylethynyl)bis(tributylphosphine)platinum(II) complexes. Molecule 1 carries two alkynyl-benzothiazolylfluorene ligands, and molecule 2 has two alkynyl-diphenylaminofluorene ligands bound to the central platinum atom. Compounds 3 and 4 possess two dihexylaminophenyl substituents at their ends and differ by the number of platinum atoms in the oligomer "core" (one vs two in 3 and 4, respectively). The ligands have strong effective two-photon absorption cross-sections, while the heavy metal platinum centers give rise to efficient intersystem crossing to long-lived triplet states. Ultrafast transient absorption and emission spectra demonstrate that one-photon excitation of the chromophores produces an S1 state delocalized across the two conjugated ligands, with weak (excitonic) coupling through the platinum centers. Intersystem crossing occurs rapidly (Kisc approximately 1011 s-1) to produce the T1 state, which is possibly localized on a single conjugated fluorenyl ligand. The triplet state is strongly absorbing (epsilonTT > 5 x 104 M-1 cm-1), and it is very long-lived (tau > 100 micro s). Femtosecond pulses were used to characterize the two-photon absorption properties of the complexes, and all of the chromophores are relatively efficient two-photon absorbers in the visible and near-infrared region of the spectrum (600-800 nm). The complexes exhibit maximum two-photon absorption at a shorter wavelength than 2lambda for the one-photon band, consistent with the dominant two-photon transition arising from a two-photon-allowed gerade-gerade transition. Nanosecond transient absorption experiments carried out on several of the complexes with excitation at 803 nm confirm that the long-lived triplet state can be produced efficiently via a sequence involving two-photon excitation to produce S1, followed by intersystem crossing to produce T1.

Syntheses and nonlinear absorption properties of conjugated porphyrin supramolecules

Self-assemblies consisting of acetylene-linked bisporphyrins with a 4-nitrophenylethynyl substituent and with a phenylethynyl substituent were synthesized. The Q-band of the phenylethynyl-substituted compound appears at 762 nm whereas that of the 4-nitrophenylethynyl-substituted one was red-shifted to 784 nm and intensified. This may be attributed to the participation of the nitro group in the π-electronic communication system. HOMOs and LUMOs were calculated for these compounds using an INDO/S-CI method. The effective two-photon absorption cross-section values of these self-assemblies were measured by using a nanosecond open aperture Z-scan method. The maximum effective two-photon absorption cross-section values of 4-nitrophenylethynyl- and phenylethynyl-substituted bisporphyrins were obtained as 1.2 × 105 GM and 8.1 × 104 GM , respectively, at 890 nm. A 1.5 enhancement factor was obtained by introducing nitro groups, which was similar to the value previously reported for ferrocene- and fullerene-connected supramolecular porphyrin.

Theoretical study of the two-photon absorption properties of octupolar complexes with Cu(I), Zn(II) and Al(III) as centers and bis-cinnamaldimine as ligands

The equilibrium geometries, electronic structures, one- and two-photon absorption (TPA) properties of a series of octupolar complexes with the Cu(I), Zn(II) and Al(III) as coordinate centers and the bis-cinnamaldimine as ligands have been studied using the B3LYP/6-31G(d) and ZINDO-SOS methods. Compared with the dipolar metal complexes, all the octupolar metal complexes (including tetrahedral and octahedral complexes) have relatively large TPA cross-sections, indicating that building octupolar metal complex is an effective route to design of promising TPA material. Lewis acidity of metal center and molecular symmetry are two important factors for enhancement of TPA cross-section of metal complex. Due to the stronger Lewis acidity of Zn(II) than Cu(I) as well as Al(III) than Zn(II), the tetrahedral Zn(II) complex exhibits a TPA cross-section larger than that of the tetrahedral Cu(I) complex, the maximum TPA position of the octahedral Al(III) complex is red-shifted relative to the octahedral Zn(II) complex, and at the same time, the octahedral Al(III) complex has a large TPA cross-section. Compared with the tetrahedral complexes, the TPA cross-sections of the octahedral complexes are enhanced due to the increased number of ligands.

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.

Calculation on the one- and two-photon absorptions properties for two series of dimethylfluorene core derivatives

Two series of dimethylfluorene core derivatives, which have different conjugation length or different peripheral substituted groups, are theoretically investigated in the paper. Using the density functional theory B3LYP with 6-31G basis set, we have obtained the equilibrium geometries and electronic structures for all the studied molecules. On the basis of the geometrical and electronic structures, the one- and two-photon absorptions properties are studied theoretically with ZINDO-SOS method in detail. The computational results are in good agreement with the available experimental values. According to our calculations, from the series I molecule to the series II counterparts, the maximum one-photon absorption (OPA) intensities and the maximum two-photon absorption (TPA) cross sections values δ max are obviously increased as the conjugation length increases. And for both series the maximum OPA wavelength λ max ( 1 ) and δ max values are increased with the stronger electron-donating or electron-accepting capability. This demonstrates that the conjugation length and the different substituent groups play important roles in the OPA and the TPA cross section.

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.

SUBSTITUENT EFFECT ON TWO-PHOTON ABSORPTION PROPERTIES OF FLUORENE DERIVATIVES

Two novel fluorene derivatives having cationic substituents were synthesized. Two-photon absorption (TPA) properties of the derivatives were evaluated using the fluorescence-based technique with a femtosecond pulse emitted from a Ti:sapphire laser. Maximum TPA cross-sections of the compounds were estimated from the TPA spectra. Based on the results, the relationship between the TPA cross-sections and the substituent effects of the derivatives were discussed.