Two-photon Spectroscopic Properties Research Articles

Nonlinear Optical Chemosensor for Sodium Ion Based on Rhodol Chromophore

As part of a strategy to identify good fluorescent probes based on two-photon excited fluorescence (TPEF), the sensor for sodium cation has been designed bearing a rhodol chromophore linked with an aza-crown ether. An efficient synthetic route to rhodol derivatives possessing five-membered heterocycles at position 9 and their precursors that contain xanthylium salt has been developed. The synthesis involves condensation of xanthylium salts bearing vinamidinium moiety at position 9, with phenylhydrazine derivatives as the key step. To accomplish the synthesis of derivatives bearing 1-aza-15-crown-5 and 1,10-diaza-18-crown-6, the Buchwald-Hartwig reaction has been employed in the final stage. Electronic spectra of all prepared rhodols display strong absorption in the range of 450-550 nm with well-resolved vibronic bands, which maintains its fine structure in a wide range of solvents. The most intensive two-photon absorption (2PA) band in the rhodol spectrum (165 GM), located at shorter wavelengths, matches well with the short-wavelength absorption band in the linear electronic spectrum and is most probably related to the two-photon allowed electronic transition S0→S2. The influence of cation binding on one- and two-photon spectroscopic properties of rhodol linked with 1-aza-15-crown-5 via the phenylpyrazole bridge has been investigated. This probe exhibits high sensitivity and good selectivity for Na(+) in CH3CN. The mechanism involves the complexation of the Na(+) by 1-aza-15-crown-5 in the probe, which induces prominent fluorescence enhancement via quenching of electron-transfer. Interestingly, the complexation with Na(+) led to a significant increase of the 2PA band in the 750-800 nm region (corresponding to a two-photon allowed, one-photon forbidden transition) for rhodol bearing 1-aza-15-crown-5, which led to the overall enhancement of the TPEF signal (approximately an order of magnitude). Thus, a turn-on fluorescent probe for sodium ion, which does not respond to many other metal species, has been constructed.

Facile Synthesis and Systematic Investigations of a Series of Novel Bent‐Shaped Two‐Photon Absorption Chromophores Based on Pyrimidine

The synthesis, structure, and single- and two-photon spectroscopic properties of a series of pyrimidine-based (bent-shaped) molecules are reported. All these stable heterocyclic compounds are fully characterized, and exhibit intense single- and two-photon excited fluorescence (SPEF and TPEF) over a wide spectral range from blue to red, with the spectral peak position of the SPEF being basically the same as that of the TPEF. The well-conjugated pi-systems, observed from the crystal structure, indicate the charge transfer feature of the ground state. Meanwhile, the theoretical and experimental studies indicate that the charge transfer from donor to acceptor is greatly enhanced in the excited states and the different substituted donor groups on the pyrimidine have a large effect on the optical and electrochemical properties. Based on typical structure data and comprehensive spectral data, the following structure-property relationships can be determined: for such bent-shaped chromophores, the absorption and the fluorescence wavelength maximum of the SPEF and TPEF, and two-photon absorption cross sections show a similar trend with increasing electron-donating strength of the corresponding terminal group and the number of branches, while the average bond lengths of the pi-linkage and HOMO-LUMO energy levels show an inverse trend. Experimental data and theoretical calculation provide a coherent picture. With these findings, bent-shaped quadrupolar chromophores combining peak TPA cross sections (up to 2280 GM), broad TPA bands throughout the whole 700-900 nm range, and high fluorescence quantum yields could, thus, be obtained. Such compounds are of particular interest for TPEF microscopy, as well as optical data storage in the visible and NIR regions. A data recording experiment proved the potential application of these materials.

Tetrastyrylarene Derivatives: Comparison of One- and Two-Photon Spectroscopic Properties with Distyrylarene Analogues

The one-photon and two-photon absorption properties of cross-shaped chromophores consisting of four donor-substituted styryl branches linked to an aromatic core (benzene or pyrazine) have been investigated and compared with those of linear analogues with only two branches (donor−π−donor distryrylarenes). The areas of the lowest energy two-photon absorption bands of the compounds with four branches were less than twice those of analogues with two branches. The spectral features observed in these chromophores suggest that electronic coupling between the branches is effective but does not lead to significant enhancement of the two-photon cross section when the branches extend in more than one dimension. In a chromophore with two donor-substituted and two acceptor-substituted branches the two-photon cross section is smaller than in the corresponding linear analogues. The main characteristics of both the one-photon and two-photon spectra of multibranched compounds of the type discussed here can be explained qualitatively within the molecular exciton description. In contrast to the case of one-photon absorptivities, the model shows that pure additivity of the two-photon absorption cross section should not be expected when two monomer units are coupled and that the cross section of the dimer depends on the relative orientation of the constituent units and on the strength and sign of the coupling interaction. In particular, the type of coupling effective in the four-branch chromophores presented here should result in a subadditivity of two-photon cross section of the monomers, in agreement with the experimental findings.

Metal induced enhancement of fluorescence and modulation of two-photon absorption cross-section with a donor–acceptor–acceptor–donor receptor

A metal ion sensing fluorophore L that exhibits a large two-photon absorption cross-section has been synthesized in good yields. The influences of different metal ion inputs, on the one- and two-photon spectroscopic properties of L, have been investigated. The ligand itself does not show any fluorescence although in presence of a metal ion like Zn(II), Cd(II), Mg(II) or Ca(II), a ∼25 time enhancement of fluorescence is observed. The ligand with symmetrical “donor–acceptor–acceptor–donor” characteristics exhibits a large two-photon absorption cross-section measured by femtosecond open-aperture Z-scan technique at 880 nm. However, presence of any of the above metal ions lowers its two-photon absorption cross-section ( δ) to different extents at 880 nm. Theoretical calculation carried out in DFT formalism on the ligand and its Zn(II) complex corroborate experimental results.

Novel pyrimidine-based amphiphilic molecules: synthesis, spectroscopic properties and applications in two-photon fluorescence microscopic imaging

This paper reports the synthesis, single- and two-photon spectroscopic properties of a series of pyrimidine-based monosubstituted D–π–A and disubstituted D–π–A–π–D type (Y shaped) molecules. Their potential applications in two-photon fluorescence microscopic imaging are also evaluated. The two-photon absorption cross-sections, measured by two-photon induced fluorescence method using a femtosecond Ti : sapphire laser as excitation source, were found to increase significantly (up to 12 times) when changing from monosubstituted molecules to their disubstituted counterparts. In addition, no significant difference in the single- and two-photon spectroscopic properties of these molecules can be observed when comparing the hydrophobic molecules (ethyl ester, 1a–4a) to the corresponding amphiphilic molecules (carboxylic acid salt, 1b–4b). However, single- and two-photon fluorescence microscopic imaging experiments revealed that the disubstituted amphiphilic molecules can efficiently stain the cytoplasmic region of Hep-G2 cells, while little or no dye uptake happened when incubating those cells with the hydrophobic molecules under the same experimental conditions.

Synthesis and spectroscopic properties of symmetrically substituted two-photon absorbing molecules with rigid elongated π-conjugation

A series of symmetrical molecules with substituted acetylene as central rigid elongated conjugation have been designed and synthesized. These molecules consist of a typical D-π-D structure, where N, N-dihexylamino and substituted acetylene are employed as donor (D) and π-conjugated center (π), respectively. Single and two-photon spectroscopic properties of these molecules were investigated systematically. One derivative with great enhancement on the two-photon absorption cross-section in 820 nm, which is among the best output wavelength range of a typical Ti:Sapphire femtosecond laser, could be obtained by inserting an anthracene ring into the rigid elongated π-conjugation. Such kind of structure modification is expected to be helpful in designing better organic nonlinear optical materials for biological imaging.

Two‐Photon Dyes Containing Heterocyclic Rings with Enhanced Photostability

A series of donor-pi-donor derivatives containing phenyl, naphthyl, and anthryl groups as the pi-center and heterocyclic rings as the conjugation bridge have been synthesized and their one- and two-photon spectroscopic properties and photostability were determined. These compounds show bathochromic shifts in the absorption and emission spectra, larger two-photon cross-section, and enhanced photostability in comparison to their open-chain analogues. In addition, a convenient method for the qualitative photostability measurement is proposed.

Strong, Low-Energy Two-Photon Absorption in Extended Amine-Terminated Cyano-Substituted Phenylenevinylene Oligomers

Three quadrupolar oligophenylenevinylenes with five rings in the conjugated backbone, terminal donor groups, and various acceptors and/or donors along the backbone were synthesized and their two-photon spectroscopic properties investigated. These chromophores exhibit large two-photon absorption cross sections over a wide wavelength range and two distinct peaks, the strongest of which (deltamax > 3600 GM) is observed at 960-970 nm, a wavelength close to twice the value of the linear absorption maximum (2lambda(1)max). The findings on these chromophores are compared with those for analogous molecules with shorter conjugation length, for which the main two-photon band is at significantly shorter wavelength than 2lambda(1)max.

Metal-ion sensing fluorophores with large two-photon absorption cross sections: aza-crown ether substituted donor-acceptor-donor distyrylbenzenes.

Chromophores based on a donor-acceptor-donor structure possessing a large two-photon absorption cross section and one or two mono-aza-15-crown-5 ether moieties, which can bind metal cations, have been synthesized. The influence of Mg(2+) binding on their one- and two-photon spectroscopic properties has been investigated. Upon binding, the two-photon action cross sections at 810 nm decrease by a factor of up to 50 at high Mg(2+) concentrations and this results in a large contrast in the two-photon excited fluorescence signal between the bound and unbound forms, for excitation in the range of 730 to 860 nm. Experimental and computational results indicate that there is a significant reduction of the electron donating strength of the aza-crown nitrogen atom(s) upon metal ion binding and that this leads to a blue shift in the position as well as a reduction in the strength of the lowest-energy two-photon absorption band. The molecules reported here can serve as models for the design of improved two-photon excitable metal-ion sensing fluorophores.

Two-photon spectroscopic properties of a new chlorin derivative photosensitizer

We report on the two-photon-excited (TPE) fluorescence spectrum and lifetime of a new chlorin derivative photosensitizer (CDP) in 0.9% NaCl solution with femtosecond laser pulses at 800 nm. The TPE fluorescence spectrum is similar to that obtained by one-photon excitation (OPE). The lifetimes of TPE and OPE fluorescence of CDP are of the order of 4.7 and 5.0 ns, respectively. The two-photon absorption (TPA) cross-section is σ 2 ′≈33.6×10 −50 cm 4 s photon −1 at 800 nm. Our results indicate that the TPE and OPE photodynamic processes of CDP are basically similar. The lifetime and TPA cross-section suggest CDP may be a potential agent for two photon fluorescent microscopy and imaging as well as a photosensitizer in photodynamic therapy.

One- and Two-Photon Spectroscopy of Donor−Acceptor−Donor Distyrylbenzene Derivatives: Effect of Cyano Substitution and Distortion from Planarity

The one- and two-photon spectroscopic properties of four symmetrically substituted donor−acceptor−donor distyrylbenzenes with either di-n-butyl- or diphenylamino donor groups and cyano acceptor groups are reported. It has been found that the position of the substitution of the electron-withdrawing cyano groups on the central phenylene ring as compared to the vinylene bond strongly affects the observed properties. In particular, the molecules with cyano substitution on the α-carbon of the vinylene linkage are characterized by weak fluorescence, short fluorescence lifetimes, and two-photon cross sections (δ) that are comparable to analogous molecules with no acceptor groups. In contrast, the molecules with acceptor substitution on the central phenylene ring are strongly fluorescent and have δ values roughly twice those of the vinyl-substituted molecules. These results are discussed in terms of the larger deviation of the conjugated backbone from planarity and the smaller distance between the donors and acce...

Ab initio study of multiphoton absorption properties of methane, ethane, propane, and butane

The low-lying electronic excited states of methane, ethane, propane, and n-butane, accessed by multiphoton absorption, have been investigated at ab initio level according to quantum electrodynamical formalisms, by utilizing RPA vertical transition energies and amplitudes. For all four alkanes, two-photon spectroscopic properties which could be detected with various experimental arrangements have been reported. For methane, the transition probability coefficients and polarization ratios for two-, three-, and four-photon single-colour absorption from plane and circularly polarized light have been evaluated. All the low-lying excitations in methane and its higher homologues are found to bear Rydberg rather than valence nature.

Ab initio calculations on the one- and two-photon electronic transitions of cyclopentadiene, spirononatetraene, 1,4-cyclo-hexadiene, Dewar benzene, norbornadiene, and barrelene

Ab initio RPA calculations have been carried out on the low-lying singlet intravalence and Rydberg electronic states, accessed by one-and two-photon absorption, of representative cyclic systems. Two-photon spectroscopic properties that could be detected under various experimental arrangements have been reported. The relative displacements of the transitions brought about by spiroconjugation and bridge insertion are correctly accounted for. Information on the nature of the first valencelike excited states has also been achieved by CI-SD treatments.

A b i n i t i o study of multiphoton absorption properties of formaldehyde, acetaldehyde, and acetone

The low-lying Rydberg and intravalence excited states of formaldehyde, acetaldehyde, and acetone, accessed by multiphoton absorption, have been investigated at ab initio level according to quantum electrodynamical formalisms, by utilizing random-phase-approximation vertical transition energies and amplitudes. For all three carbonyls, two-photon spectroscopic properties which could be detected with various experimental arrangements have been reported. For formaldehyde, an exhaustive overview on spectroscopic observables associated with multiphoton absorption is presented. The transition probability coefficients and polarization ratios for two-, three-, and four-photon single-color absorption from plane polarized, circularly polarized, and unpolarized light have been evaluated. The molecular response to concerted absorption of two and three photons from two laser beams under various polarization conditions has been investigated as a function of the photon energies. An attempt has also been made to estimate the magnitude and direction of the electrochromic changes in two-photon spectroscopic properties brought about by an external static electric field.