A superfluorescent fluorenyl probe with efficient two-photon absorption

The linear photophysical, excited state absorption (ESA), superfluorescence, and two-photon absorption (2PA) properties of 4,4'-(1E,1'E)-2,2'-(7,7'(1E,1'E)2,2'(4,4'-sulfonylbis(4,1-phenylene))bis(ethane-2,1-diyl)bis(9,9-didecy-9H-fluorene7,2-diyl))bis(ethane-2,1-diyl)bis(N,N-diphenylaniline) (1) were investigated in organic and aqueous media with respect to its potential application in biological imaging. The analysis of linear photophysical properties revealed a rather complex nature of the main one-photon absorption band, strong solvatochromic effects in the steady-state fluorescence spectra, single-exponential fluorescence decay, and high fluorescence quantum yields in organic solvents (≈1.0). The ESA spectra of 1 suggested potential for light amplification in nonpolar media while efficient superfluorescence in cyclohexane was demonstrated. The degenerate 2PA spectra of 1 were obtained over a broad spectral range (640-900 nm), using a standard two-photon induced fluorescence method under 1 kHz femtosecond excitation. Two well defined 2PA bands with maximum 2PA cross sections up to 1700 GM in the higher energy, short wavelength band and ≈1200 GM in the lower energy, long wavelength band of 1 were shown. The potential use of 1 in bioimaging was demonstrated via one- and two-photon in vitro fluorescence imaging of HCT 116 cells.     

Design of dipicolinic acid ligands for the two-photon sensitized luminescence of europium complexes with optimized cross-sections

The multistep synthesis of an extensive series of push-pull donor-pi-conjugated dipicolinic acid ligands is described. The charge transfer character of the ligand can be tuned by changing the donor group (CH 2R, OR, SR, or NR 2) or the nature of the conjugated backbone (phenyl, phenylethynyl, naphtylethynyl, bis(phenylethynyl), or chalcone). The photophysical properties of related D 3 symmetric europium complexes (absorption and luminescence) were measured. Experiments using two-photon sensitized luminescence of a Eu (III) complex reveal large two-photon absorption (TPA) cross-section values (775 GM at 740 nm) in dichloromethane. Furthermore, some structure-property relationships can be derived from this systematic study, allowing an optimization of TPA properties of lanthanide complexes.     

Transient excited-state absorption and gain spectroscopy of a two-photon absorbing probe with efficient superfluorescent properties

The synthesis, linear photophysical properties, two-photon absorption (2PA), excited-state transient absorption, and gain spectroscopy of a new fluorene derivative tert-butyl 4,4'-(4,4' (1E,1'E)-2,2'-(9,9-bis(2- (2-ethoxyethoxy)ethyl)-9H-fluorene-2,7-diyl)bis(ethene-2,1-diyl)bis(4,1 phenylene)]dipiperazine-1-carboxylate (1) are reported. The steady-state linear absorption and fluorescence spectra, along with excitation anisotropy, fluorescence lifetimes, and photochemical stability of 1 were investigated in a number of organic solvents at room temperature. The 2PA spectra of 1 with a maximum cross-section of ~ 300 GM were obtained with a 1 kHz femtosecond laser system using open-aperture Z-scan and two-photon-induced fluorescence methods. The transient excited-state absorption (ESA) and gain kinetics of 1 were investigated by a femtosecond pump-probe methodology. Fast relaxation processes (~1-2 ps) in the gain and ESA spectra of 1 were revealed in ACN solution, attributable to symmetry-breaking effects in the first excited state. Efficient superfluorescence properties of 1 were observed in a nonpolar solvent under femtosecond excitation. One- and two-photon fluorescence microscopy imaging of HCT 116 cells incubated with probe 1 was accomplished, suggesting the potential of this new probe in two-photon fluorescence microscopy bioimaging.     

The synthesis and photophysical studies of cyclometalated Pt(II) complexes with C,N,N-ligands containing imidazolyl donors

Two new C,N,N-type ligands (HL(2) and HL(3)), containing a C(phenyl), a N(pyridyl), and a N(imidazolyl) donor, and their cycloplatinated complexes, [Pt(L(2))Cl] (1), [Pt(L(3))Cl] (2), [Pt(L(2))(PPh(3))](+) (3) and [Pt(L(3))(PPh(3))](+) (4), have been successfully synthesized and characterized. Spectroscopic and (3)MLCT luminescent properties of these Pt(II) cyclometalated complexes were found to be pH dependent. This was attributed to the protonation/deprotonation of the acidic 1-imidazolyl-NH moieties on the ligands. All the cycloplatinated complexes (both protonated and deprotonated forms) possessed two-photon excitability with two-photon absorption cross-sections ranging from 6.0 to 30.0 GM (protonated forms) and from 16.2 to 24.9 GM (deprotonated forms).     

双光子激发的超分子聚合物纳米颗粒生物成像研究

将具有双-2-脲基-4[1H]-嘧啶酮（bisUPy）的β-二羰基氟硼类衍生物（BF₂-bisUPy）及卟啉衍生物（Por（Pt）-bisUPy）通过四重氢键作用组装成超分子聚合物,通过微乳液法制备成在水中均匀分散的超分子聚合物纳米颗粒（SPNP）。扫描电子显微镜形貌表征表明获得的纳米颗粒粒径约为60 nm。紫外-可见吸收光谱、荧光发射光谱及寿命衰减实验均证明纳米颗粒内BF₂-bisUPy与Por（Pt）-bisUPy可发生高效的能量传递。具有双光子吸收的BF₂-bisUPy作为能量供体,可通过荧光共振能量传递（FRET）增强双光子激发下Por（Pt）-bisUPy的发光。双光子激发荧光强度与激光功率测试表明所制备的超分子聚合物纳米颗粒具有强烈的双光子激发下的荧光及磷光双发射,这种纳米材料可进入细胞,具有优秀的生物相容性,并在双光子激发时表现出强烈的荧光和磷光双发射生物成像。     

Structural, photophysical, and nonlinear absorption properties of trans-di-arylalkynyl platinum(II) complexes with phenyl and thiophenyl groups

Optical power limiting and luminescence properties of two Pt(II) complexes with thiophenyl and phenyl groups in the ligands, trans-Pt(P(n-Bu)3)2(C[triple bond]C-Ar)2, where Ar = -C4H2S-C[triple bond]C-p-C6H4-n-C5H11 (1) and -p-C6H4-C[triple bond]C-C4H3S (2), have been investigated. The fluorescence lifetimes were found to be on the sub-nanosecond time scale, and the quantum yields were low, in accord with fast intersystem crossing from the excited singlet to triplet manifold. The phosphorescence lifetimes of 1 and 2 were shorter than that of a Pt(II) complex having two phenyl groups in the ligands. In order to elucidate the C-Pt bonding nature in the ground state, the 13C NMR chemical shift of the carbon directly bonded to Pt, the coupling constants 1JPtC, 2JPtC, and 1JPtP, and IR nuC[triple bond]C wavenumbers were obtained for 1, 2, and three other trans-diarylalkynyl Pt(II) complexes. X-ray diffraction data of 1 and 2 and density functional theory calculated geometries of models of 1, 2, and trans-Pt(P(n-Bu)3)2(C[triple bond]C-p-C6H4-C[triple bond]C-C6H5)2 (3) show that 1 preferably exists in a different conformation from that of 2 and 3. The variations in photophysical, NMR, and IR data can be rationalized by differences in geometry and pi-backbonding from Pt to the alkynyl ligand.     

Temperature effect on the optical properties of two different triphenylamine-based organic dyes

In this paper, we present the absorption and photoluminescence (PL) spectra of conjugated, metal-free organic dyes, triphenylamine derivatives 3-(4-(bis(4-(5-(4-(hexyloxy)phenyl)thiophenyl)phenyl)amino)phenyl)-2-cyanoacrylic acid (OD3) and (E)-3-(5′-(4-(bis(4-(5-(4-hexyloxy)phenyl)thiophen-2-yl)phenyl)amino)phenyl)-2,2′-bithiophen-5-yl)-2-cyanoacrylic acid (OD3DT), with and without a π-conjugated bridge, respectively, in film at a temperature range from 13 to 400 K. We find that the intensities of absorption and PL of OD3 decrease gradually beyond 200 K, as well as the ratios of integral areas of absorption to PL spectra. However, the other compound, OD3DT, shows a very different behavior. An increase is discovered in the ratio of the absorption to PL integral area when the temperature is higher than 200 K. A π-conjugated bridge gives this compound a higher degree of symmetry, and therefore, a better alignment of the molecules in the film, which causes a stacking aggregation such that the temperature effect on this compound is different than OD3.     

Synthesis and characterizations of star-shaped octupolar triazatruxenes-based two-photon absorption chromophores

A series of star-shaped octupolar triazatruxenes (TATs, 1-6) with intramolecular "push-pull" structure were synthesized and their photophysical properties have been systematically investigated. These chromophores showed obvious solvatochromic effect, i.e., significant bathochromic shift of the emission spectra and larger Stokes shifts were observed in more polar solvents mainly due to photoinduced intramolecular charge transfer (ICT). The two-photon absorption (2PA) cross-section values were determined by two-photon excited fluorescence (2PEF) measurements in toluene and THF. These chromophores exhibited large two-photon absorption cross-sections ranging from 280 to 1620 GM in the near-infrared (NIR) region. Compound 6 showed the largest 2PA action cross-section (σ(2)Φ) of 564 GM and could be a potential two-photon fluorescent (2PF) probe. In addition, compounds 1-6 all displayed good thermal stability and photostability.     

Modulating the photophysical properties of azamacrocyclic europium complexes with charge-transfer antenna chromophores

Two europium complexes with bis(bipyridine) azamacrocyclic ligands featuring pendant arms with or without π-conjugated donor groups are synthesized and fully characterized by theoretical calculations and NMR spectroscopy. Their photophysical properties, including two-photon absorption, are investigated in water and in various organic solvents. The nonfunctionalized ligand gives highly water-stable europium complexes featuring bright luminescence properties but poor two-photon absorption cross sections. On the other hand, the europium complex with an extended conjugated antenna ligand presents a two-photon absorption cross section of 45 GM at 720 nm but is poorly luminescent in water. A detailed solvent-dependent photophysical study indicates that this luminescence quenching is not due to the direct coordination of O-H vibrators to the metal center but to the increase of nonradiative processes in a protic solvent induced by an internal isomerization equilibrium.     

Single- and two-photon properties of a dye-derivatized Roussin's red salt ester (Fe2(mu-RS)2(NO)4) with a large TPA cross section

The synthesis, characterization, photochemistry, and two-photon photophysical properties of a new dye-derivatized iron sulfur nitrosyl cluster Fe2(mu-RS)2(NO)4 (AFX-RSE, RS = 2-thioethyl ester of N-phenyl-N-(3-(2-ethoxy)phenyl)-7-(benzothiazol-2-yl)-9,9-diethyl-fluoren-2-yl-amine) were investigated. Under continuous photolysis, AFX-RSE decomposes with modest quantum yields (Phi(diss) = (4.9 +/- 0.9) x 10(-3) at lambda(irr) = 436 nm) as measured from the loss of the nitrosyl bands in the IR absorbance spectrum. Nitric oxide (NO) was qualitatively demonstrated to be photochemically produced via single-photon excitation through the use of an NO-specific electrode. Steady-state luminescence measurements have shown that AFX-RSE fluorescence is about 88% quenched relative to the model compound AF-tosyl. This is attributed to a relatively efficient energy transfer from the excited states of the antenna chromophores to the dinuclear metal center, with the subsequent production of NO. In addition, the two-photon absorption (TPA) cross sections (delta) were measured for the AF-chromophores via the two-photon excitation (TPE) photoluminescence technique using a femtosecond excitation source. The TPA cross section of AFX-RSE was found with this technique to be delta = 246 +/- 8 GM (1 GM = 10(-50) cm4 s photon(-1) molecule(-1)).     

吡啶星型分子的双光子上转换荧光特性

用飞秒Ti:sapphire激光测定了一种星型吡啶分子2,5-二{4-{4-[N,N-二(4-吡啶乙烯基)苯基氨基]苯乙烯基}苯基}-1,3,4-噁二唑(PyPASPO)的双光子吸收截面及上转换荧光光谱.采用非线性透过率法测得二氯甲烷和四氢呋喃溶液中的其双光子吸收截面分别为412.5 和288.8 GM. 系统研究了吡啶星形分子PyPASPO的线性吸收和透过、单光子荧光、荧光寿命及激发-发射三维荧光谱和前线轨道能级. 在800 nm和150 fs钛宝石激光器激发下PyPASPO在二氯甲烷和四氢呋喃溶液中的双光子上转换荧光发射波长分别位于571和 525 nm,在二氯甲烷溶液中单光子荧光峰位于532 nm,荧光寿命为1.24 ns. HOMO和LUMO能级分别为-5.21 eV和-2.92 eV.增大分子内电荷转移有效增强了吡啶星形分子的双光子吸收和双光子上转换荧光发射能力     

两个具有强双光子荧光的有机硼化合物

以二米基硼为电子受体, 苯乙烯基噻吩为共轭桥, 合成了两个新的稳定的有机硼化合物: 反式,反式-2-二米基 硼-5-{2-[4-(2-噻吩乙烯基)苯基]乙烯基}噻吩(1)和反式,反式-1,4-二-[2-(5-二米基硼噻吩)乙烯基]苯(2). 前者为不对称结构的偶极分子, 后者为对称的A-π-A型四极分子. 对称性不同的化合物表现出不同的双光子吸收性质. 对于偶极分子1, 单双光子吸收达到的激发态能级接近, 而对于四极分子2, 双光子吸收达到的激发态则比单光子吸收所达到的激发态高出0.35 eV. 在波长为710到 900 nm范围的飞秒脉冲激光激发下, 化合物1和2在THF溶液中都可以发出很强的绿色上转换荧光 (1, λ_max＝505 nm; 2, λ_max＝513 nm). 用双光子荧光法测得A-π-A型化合物2在775 nm处的双光子吸收截面达1340 GM.     

Theoretical investigation of one- and two-photon absorption properties of platinum acetylide chromophores

In this paper, we have theoretically investigated bis((4-phenylethynyl)phenyl) ethynyl)bis(trimethylphosphine)platinum(II) (PE2) and its analogs three platinum acetylide complexes (1-3) that feature highly pi-conjugated ligands (alkynyl-dimethylfluorene substituted with electron-donating or -withdrawing moieties). The geometrical and electronic structures are calculated at the ECP60MWB//6-31G*(H, C, P, N, S) basis set level by the density functional theory (DFT) method; one-photon absorption properties have been calculated by using time-dependent DFT (TDDFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods, and two-photon absorption (TPA) properties are obtained with the ZINDO/sum-over-states method. The values of beta(sp) and beta(d) for Pt are adjusted to -1 eV and -28.5 eV, respectively, to make one-photon absorption spectra calculated by ZINDO closest to the experimental data and TDDFT results. The calculated results indicate that all molecules in this work (involving cis isomers of molecules 1-3) take on two TPA peaks in the 600-800 nm region. The peak at 700-750 nm should not be simply attributed to the appearance of noncentrosymmetric cis isomers in solution, although trans and cis isomers adhere to a different selection rule. Every TPA peak results from its transition character. Molecules 1-3 show greater two-photon absorption strength compared with PE2 and retain good transparency.     

Synthesis and properties of tribranched chromophores with triazine and fluorene units

Two tribranched chromophores,1,3,5-triazine as electron deficient core,9,9-dimethylfluorene asπ-conjugated bridge, diphenylamino(4a) and naphthylamino(4b) as electron-donating end-groups,were successfully prepared via Buchwald-Hartwig coupling reaction.Their linear photophysical and two-photon absorption(TPA) properties were investigated by absorption, fluorescence and nonlinear transmission method,respectively.The absorption cut-offs of the chromophores are below 550 nm and both chromophores have strong fluorescence emission.The compound 4a(206.3 GM) exhibits larger TPA cross-section than 4b (57.8 GM) in the femtosecond regime at 800 nm.     

High-resolution electronic spectra of ethylenedioxythiophene oligomers

The photophysical properties of a series of 3,4-ethylenedioxythiophene oligomers (OEDOT) with up to five repeat units are studied as function of conjugation length using absorption, fluorescence, phosphorescence, and triplet-triplet absorption spectroscopy at low temperature in a rigid matrix. At 80 K, a remarkably highly resolved vibrational fine structure can be observed in the all electronic spectra which reveals that the electronic structure of the oligomers strongly couples to two different vibrational modes (approximately 180 and approximately 50 meV). The energies of the 0-0 transitions in absorption, and fluorescence, phosphorescence, and triplet-triplet absorption all show a reciprocal dependence on the inverse number of repeat units. The triplet energies inferred from the phosphorescence spectra are accurately reproduced by quantum chemical DFT calculations using optimized geometries for the singlet ground state (S0) and first excited triplet state (T1). Using vibrational IR and Raman spectroscopy and quantum chemical DFT calculations for the normal modes in the ground state, we have been able to assign the vibrations that couple to the electronic structure to fully symmetric normal modes. The high-energy mode is associated with the well-known carbon-carbon bond stretch vibration, and the low-energy mode involves a deformation of the bond angles within the thiophene rings and a change of C-S bond lengths. Experimentally obtained Huang-Rhys parameters and theoretical normal mode deformations are used to analyze the geometry changes between T1 and S0 and to semiexperimentally predict the geometry in the S1 state for 2EDOT.     

Phosphorescent Cu(I) complexes of 2-(2'-pyridylbenzimidazolyl)benzene: impact of phosphine ancillary ligands on electronic and photophysical properties of the Cu(I) complexes

Four mononuclear Cu(I) complexes of 2-(2'-pyridyl)benzimidazolylbenzene (pbb) with four different ancillary phosphine ligands PPh(3), bis[2-(diphenylphosphino)phenyl]ether (DPEphos), bis(diphenylphosphino)ethane (dppe), and bis(diphenylphosphinomethyl)diphenylborate (DPPMB) have been synthesized. The crystal structures of [Cu(pbb)(PPh(3))(2)][BF(4)] (1), [Cu(pbb)(dppe)][BF(4)] (2), [Cu(pbb)(DPEphos)][BF(4)] (3), and the neutral complex [Cu(pbb)(DPPMB)] (4) were determined by single-crystal X-ray diffraction analyses. The impact of the phosphine ligands on the structures of the copper(I) complexes was examined, revealing that the most significant impact of the phosphine ligands is on the P-Cu-P bond angle. The electronic and photophysical properties of the new complexes were examined by using UV-vis, fluorescence, and phosphorescence spectroscopies and electrochemical analysis. All four complexes display a weak MLCT absorption band that varies considerably with the phosphine ligand. At ambient temperature, no emission was observed for any of the complexes in solution. However, when doped into PMMA polymer (20 wt %), at ambient temperature, all four complexes emit light with a color ranging from green to red-orange, depending on the phosphine ligand. The emission of the new copper complexes has an exceptionally long decay lifetime (>200 micros). Ab initio MO calculations established that the lowest electronic transition in the copper(I) complexes is MLCT in nature. The electronic and photophysical properties of the new mononuclear Cu(I) complexes were compared with those of the corresponding polynuclear Cu(I) complexes based on the 2-(2'-dipyridyl)benzimidazolyl derivative ligands and the previously extensively studied phenanthroline-based Cu(I) complexes.     

Altering the emission behavior with the turn of a thiophene ring: the photophysics of condensed ring systems of alternating benzenes and thiophenes

Six aromatic compounds with embedded thiophenes differing in the number of rings (2-5) and thiophene orientation along the long axis of the molecule (syn, anti) were investigated. Photophysical properties, steady-state absorption, fluorescence, phosphorescence, lifetimes, quantum yields, and a comprehensive time-resolved spectroscopic analysis (femtosecond and nanosecond transient absorption spectroscopy) have been studied as a function of molecular structure.     

9-戊基咔唑-3,6-双-(炔苯基-4-甲酸乙酯)的合成与双光子特性研究

采用钯催化的碳碳偶合反应合成了9-戊基咔唑-3,6-双-(炔苯基-4-甲酸乙酯)(I).进一步研究了化合物I在四氢呋喃和40%四氢呋喃水溶液中的光物理性质,结果显示,化合物I在40%四氢呋喃水溶液中的紫外吸收峰位置与其四氢呋喃溶液相比没有发生明显移动,它在40%四氢呋喃水溶液中的单光子荧光发射峰出现在453 nm,较其在四氢呋喃溶液的发射有42 nm红移,其荧光量子效率为0.44.用波长为660 nm飞秒激光激发时,化合物I在40%四氢呋喃水溶液中的双光子荧光发射最大峰红移至489 nm,其双光子吸收截面值为251GM,比其在四氢呋喃溶液中的截面(151 GM)增强了60%.     

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.     

Application of density functional theory for studies of excited states and phosphorescence of platinum(II) acetylides

The electronic states of different conformations of platinum acetylides Pt(PH3)2(C[triple bond]C-Ph)2 and Pt(PH3)2(C[triple bond]C-PhC[triple bond]C-Ph)2 (PE1 and PE2) were calculated with density functional theory (DFT) using effective core potential basis sets. Time dependent DFT calculations of UV absorption spectra showed strong dependence of the intense absorption band maxima on mutual orientation of the phenyl rings with respect to the P-Pt-P axis. Geometry optimization of the first excited triplet state (T1) indicates broken symmetry structure with the excitation being localized in one ligand. This splits the two substitution ligands into a nondistorted aromatic ring with the C[triple bond]C-Ph bonds for one side and into a quinoid structure with a cumulenic C=C=C link on the other side. Quadratic response (QR) calculations of spin-orbit coupling and phosphorescence radiative lifetime (tauR) indicated a good agreement with experimental tauR values reported for solid PE1 and PE2 and PE2 capped with dendrimers in tetrahydrofuran solutions. The QR calculations reproduced an increase of tauR upon prolongation of pi chain of ligands and concommittant redshift of the phosphorescence. Moreover, it is shown how the phosphorescence borrows intensity from sigma-->pi* transitions localized at the C[triple bond]C-Pt-P fragments and that there is no intensity borrowing from delocalized pi-->pi* transitions.