Quantum-sized gold clusters as efficient two-photon absorbers

The two-photon absorption properties of Au25 cluster has been investigated with the aid of two-photon excited fluorescence in the communication wavelength region with a cross-section of 2700 GM at 1290 nm. Additional visible fluorescence has been discovered for small gold clusters which is two-photon allowed (after excitation at 800 nm), and the absolute cross-section has been determined for gold clusters with number of gold atoms varying from 25 to all the way up to 2406 using one and two-photon excited time-resolved fluorescence upconversion measurements. Record high TPA cross-sections have been measured for quantum sized clusters making them suitable for two-photon imaging as well as other applications such as optical power limiting and lithography.     

1,2,3,4-四氢喹啉-4-酮衍生物的线性及非线性光学性质

合成了一系列具有刚性结构的推拉型1,2,3,4-四氢喹啉-4-酮衍生物: 1-苄基-1,2,3,4-四氢喹啉-4-酮(BTHQ)、2-(1,2,3,4-四氢喹啉-4-叶立德)丙二腈(THQM)、1,6-二羰基久洛尼定(DOJ)和1,6-二(二氰甲烯基叶立德)久洛尼定(BDCJ).测定了其吸收光谱、单光子荧光光谱和双光子上转换荧光光谱. 这类化合物的单双光子荧光参数都存在着很强的、规则的溶剂效应, 表明分子激发态可能存在较大的极性. 它们的二氯甲烷溶液在800 nm飞秒激光(150 fs)照射下, 能够发射出很强的双光子上转换荧光. 采用非线性透过率法测得四个化合物的双光子吸收截面在0.83～23.95×10－50 cm4•s•photon－1之间. 这类化合物的激发态存在有效的分子内电荷转移, 对双光子吸收和双光子荧光发射有较大贡献.     

Metal ion sensing novel calix[4]crown fluoroionophore with a two-photon absorption property

1,3-Alternate calix[4]arene-based fluorescent chemosensors bearing two-photon absorbing chromophores have been synthesized, and their sensing behaviors toward metal ions were investigated via absorption band shifts as well as one- and two-photon fluorescence changes. Free ligands absorb the light at 461 nm and weakly emit their fluorescence at 600 nm when excited by UV-vis radiation at 461 nm, but no two-photon excited fluorescence is emitted by excitation at 780 nm. Addition of an Al(3+) or Pb(2+) ion to a solution of the ligand causes a blue-shifted absorption and enhanced fluorescence due to a declined resonance energy transfer (RET) upon excitation by one- and two-photon processes. Addition of a Pb(2+) ion to a solution of 1.K(+) results in a higher fluorescence intensity than the original 1.Pb(2+) complex regardless of one- or two-photon excitation, due to the allosteric effect induced by the complexation of K(+) with a crown loop.     

三苯胺-噁二唑超支化共轭聚合物的多光子泵浦绿色荧光

采用钯催化Heck反应制备了一种新型三苯胺-噁二唑超支化荧光聚合物PI. 用飞秒Ti:sapphire激光研究了PI的三光子和双光子上转换荧光光谱, 激发波长位于近红外区(800~1350 nm). 在1280 nm和80 fs激光激发下, PI的三光子上转换荧光发射波长分别为525 nm(THF), 534 nm(CH2Cl2)和578 nm(DMF). 在800 nm和150 fs激光激发下, PI的双光子上转换荧光发射波长分别为527 nm(THF), 532 nm(CH2Cl2)和573 nm(DMF). 采用非线性透过率法测定荧光聚合物PI的三光子和双光子吸收系数. 系统研究了PI的线性吸收和透过、单光子荧光、荧光寿命、前线轨道能级及热稳定性. 实验结果表明, 三苯胺-噁二唑超支化共轭聚合物的多光子吸收和上转换荧光发射性能比树型分子或线型聚合物更为优异.     

Synthesis and photophysical properties of three (multi)branched planar molecules

Three thiophenevinyl substituted one-, two-, and three-branched truxene π-conjugated compounds TS1, TS2 and TS3 have been prepared using a Heck reaction. Their linear absorption, single- and two-photon excited fluorescence were examined. The three analogues emit blue fluorescence at 420 nm. The number of branches has no influence on the position of the absorption maxima of the charge transfer band and fluorescence emitting maxima. However, the molar extinction coefficients of charge transfer band increase almost linearly with the number of branches. The two-photon absorption cross-section of the octupolar three-branched compound TS3 is several times that of the two-branched compound TS2 and one-branched compound TS1.     

Synthesis and Ultrafast Broadband Optical Limiting Properties of a Two-Branched Twistacene

A novel two-branched twistacene (PyDN) has been designed and synthesized for application on ultrafast optical limiting. This twistacene exhibits excellent two photon absorption and two photon absorption-induced excited singlet state absorption, which was systematically investigated with a femtosecond Z-scan experiment, transient absorption spectrum, and two-photon excited fluorescence experiments. The admirable two photon absorption is attributed to the high degree of π electron delocalization in twistacene which is caused by introduction of two strong donors. The excited singlet state absorption cooperates with two-photon absorption to provide an excellent ultrafast optical limiting behavior with high linear transmittance, where the thresholds are 2.3–5.3 mJ/cm² in the spectral region of 532–800 nm of femtosecond laser and 133 mJ/cm² for picosecond pulse at 532 nm. These thresholds are lower than that of most of the optical limiters reported previously, which indicates PyDN is a promising candidate for ultrafast optical limiting.     

1,3,4-噁二唑衍生物的双光子吸收和双光子泵浦荧光

依据“推电子基-共轭中心-拉电子基-共轭中心-推电子基”的模型将电荷传输型1,3,4-噁二唑环嵌入芳香共轭体中, 通过Wittig-Horner反应合成了2种对称型强双光子吸收和双光子诱导荧光分子2,5-二[4-(2-芳基乙烯基)苯基]-1,3,4-噁二唑. 它们的氯仿溶液在锁模Nd: YAG激光器800 nm激光照射下, 发射出很强的双光子上转换荧光, 其最强荧光分别在波长507和475 nm. 采用非线性透过率法测得其双光子吸收截面分别为1.07×10^－46和6.6×10^－47 cm⁴•s•photon^－1. 这2个对称型D-π-A-π-D生色分子从激发端基到π共轭桥的有效能量传输, 对双光子吸收和双光子荧光发射能力贡献较大.     

Excited-state symmetry and reorientation dynamics of perylenes in liquid solutions: time-resolved fluorescence depolarization studies using one- and two-photon excitation

The excited-state symmetry and molecular reorientation of perylene, 1,7-diazaperylene, and 2,5,8,11-tetra- tert-butylperylene have been studied by different fluorescence depolarization experiments. The first excited electronic singlet state was reached through one-photon excitation (OPE) and two-photon excitation (TPE). A 400 and 800 nm femtosecond laser pulse was used for this purpose, and data were collected by means of the time-correlated single-photon counting technique. It is found that the rotational correlation times for each perylene derivative are very similar in the OPE and TPE depolarization experiments. For the determination of the two-photon absorption tensor, a recently described theoretical model has been applied (Ryderfors et al. J. Phys. Chem. A 2007, 111, 11531). It was found that the two-photon process can be described by a 2 x 2 absorption tensor for which the components are solvent dependent and exhibit mixed vibronic character. In the dipole approximation this is compatible with a parity-forbidden two-photon absorption into the first excited singlet state.     

多支结构的吡嗪衍生物的合成及其双光子吸收性质

合成了一系列含有双支、三支和四支的吡嗪衍生物, 测定了它们的线性吸收和发射性质以及双光子吸收和发射性质. 随着吡嗪环上侧链数目的增加(支链数目从2到4), 吸收光谱(吸收峰位于290～390 nm)、荧光谱(发射峰位于400～510 nm)和双光子荧光谱(激发波长720 nm)都发生红移, 荧光量子产率也逐渐增强(从0.13增大到0.25). 另外, 从双支到四支结构, 双光子吸收截面σ按照1∶2.8∶3.7的比例增加, 接近于支链数目的平方之比(1∶2.25∶4), 表明多支结构的双光子吸收存在显著的增强效应, 其中四支结构的σ值为1007 GM. 实验中还发现, 对于具有相同支链数目的化合物, 邻、对位的取代模式比间位取代模式具有更强的单光子和双光子荧光性质.     

Competition between photodissociation and photoionization in methyl iodide

CH₃I has a number of 5pπ → 6p Rydberg states which can be excited by two-photon absorption from the ground state. These two-photon absorptions have been previously detected by molecular ionization with a third photon. They can also be studied by observation of the VUV fluorescence from neutral photofragments (excited iodine atoms) following absorption of a third photon. Similarly it is found that absorption of one photon at 118 nm (10.5 eV) is followed by dissociation into excited iodine atoms as well as ionization. Iodine atom VUV emission is 2–10 times stronger from CD₃I than from CH₃I.     

The symmetry of two-photon excited states as determined by time-resolved fluorescence depolarization experiments

A new experimental and theoretical approach is presented for the quantitative determination and assignment of the two-photon absorption tensor of fluorophores dissolved in liquid solutions. Two linearly independent time-resolved fluorescence anisotropies and the two-photon polarization ratio were determined from experiments based on using the time-correlated single photon counting technique. The data were analyzed in a global manner under the assumption of prevailing diffusive molecular reorientations and when accounting for the influence of rapid unresolved reorientations. The method has been applied in fluorescence studies of perylene, two-photon excited at 800 nm. The analysis suggests that the two-photon transition is mediated via vibronic coupling including at least two vibrations of different symmetry, and also that the first singlet excited electronic state acts as a dominating intermediate state.     

Fluorescence of proteins induced by two-photo absorption

At room temperature, the UV fluorescence of trypsin, thyroglobulin, hemoglobin and ablumin are observed; these molecules undergo two-photon absorption when they are excited with the radiation of a frequency-duplicated Q-switched Nd:YAG laser. It is shown that the fluorescence of these proteins comes from the tryptophan residues and that it has a red shift of about 20 nm relative to the one-photon fluorescence. We suggest that the weak emission from tyrosine arises from the forbidden two-photon transition. The influence of concentration on the fluorescence of hemoglobin and tryptophan is discussed. The two-photon absorption cross-sections are estimated.     

Singlet oxygen generation via two-photon excited FRET

A new approach to two-photon excited photodynamic therapy has been developed. A dendritic array of eight donor chromophores capable of two-photon absorption (TPA) was covalently attached to a central porphyrin acceptor. Steady-state fluorescence measurements demonstrated that the donor chromophores transfer excited-state energy to the porphyrin with 97% efficiency. Two-photon excitation of the donor chromophores at 780 nm resulted in a dramatic increase in porphyrin fluorescence relative to a porphyrin model compound. Enhanced singlet oxygen luminescence was observed from oxygen-saturated solutions of the target compound under two-photon excitation conditions.     

Fluorescence of proteins induced by two-photon absorption

At room temperature, the UV fluorescence of trypsin, thyroglobulin, hemoglobin and albumin are observed; these molecules undergo two-photon absorption when they are excited with the radiation of a frequency-duplicated Q-switched Nd:YAG laser. It is shown that the fluorescence of these proteins comes from the tryptophan residues and that it has a red shift of about 20 nm relative to the one-photon fluorescence. We suggest that the weak emission from tyrosine arises from the forbidden two-photon transition. The influence of concentration on the fluorescence of hemoglobin and tryptophan is discussed. The two-photon absorption cross-sections are estimated.     

Synthesis, Characterization and Non-linear Optical Properties of a New Organic Dye： DEAHAS

Two-photon absorption (TPA) is a process in which two photons are simultaneously absorbed to an excited state via a virtual state. The synthesis of organic optical materials with large TPA cross section has become a subject of great interest in recent years due to various application such as three-dimensional fluorescence imaging1, optical data storage2,3 and lithographic microfabrication4-6. Recently we have synthesized a new organic dye DEAHAS that is a symmetrically substituted stilbe…     

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.     

Novel Y-type two-photon active fluorophore: synthesis and application in fluorescent sensor for cysteine and homocysteine

A novel Y-shaped two-photon active material FD3 based on the imidazole core has been synthesized and exhibited intense two-photon excited fluorescence with two-photon absorption cross-section of more than 9000 GM. Importantly, FD3 could be used as a potential two-photon excited fluorescent sensor for cysteine and homocysteine.     

Photophysical properties of octupolar chromophore based on triazine core and fluorene divinylene conjugated bridge

A novel octupolar chromophore with 1,3,5-triazine as core,2,7-divinylene-9,9-dimethylfluorene as extendedπ-conjugated bridge,triarylamine as the electron-donating end-groups was successfully synthesized and characterized.Their linear photophysical and two-photon absorption(TPA) properties were investigated by UV absorption,excited fluorescence(SPEF) spectra and nonlinear transmission method,respectively.The absorption cut-off of the chromophore is below 520 nm and it has stronger fluorescence emission in a nonpolar solvent.In addition,the chromophore exhibits larger TPA cross-section(226.0 GM) in the femtosecond regime at 800 nm.     

Dipicolinate as acceptor in D-π-A chromophores: synthesis, characterization and fluorescence following single- and two-photon excitation

Three novel donor-π-acceptor type compounds with dipicolinate as acceptor have been synthesized. Their absorption, photoluminescence as well as their two-photon absorption properties have been investigated. Two of them show strong two-photon absorption and two-photon excited up-conversion fluorescence.     

Blue two-photon excited fluorescence of several D-π-D, A-π-A, and D-π-A compounds featuring dimesitylboryl acceptor

Several donor-π-donor (D-π-D), acceptor-π-acceptor (A-π-A), and donor-π-acceptor (D-π-A) types of organic compounds with fluorene as π bridge and dimesitylboryl group as electron acceptor, which show strong two-photon excited blue fluorescence, have been synthesized and structurally investigated. The symmetric A-π-A type of compound exhibits the shortest wavelength of two-photon excited fluorescence (TPEF) at λ_em=405 nm under the excitation of λ_ex=730 nm; the unsymmetric D-π-A type of compound with diphenylamino as donor exhibits the most intense TPEF at blue region (λ_em=484 nm) with a two-photon absorption cross-section of 425 GM under λ_ex=800 nm.