Strong two photon absorption and photophysical properties of symmetrical chromophores with electron accepting edge substituents

Two photon absorption (TPA) and photophysical properties of three new symmetrical chromophores with electron accepting phthalimide edge substituents have been studied. The three chromophores contain fluorene, alcoxy-substituted divinyl benzene, and carbazole moieties as central cores, respectively. The femtosecond time-resolved fluorescence upconversion spectroscopy and two photon excited fluorescence technique have been carried out. The effect of solvent polarity on TPA and on photophysics has also been determined. Ultrafast fluorescence dynamics, with decay times ranging from 1 to 13 ps, are revealed in polar solvents. This is attributed to the relaxation of the chromophores to the intramolecular charge transfer state. The chromophore bearing fluorene central core, being of the type A-pi-A, is the most efficient concerning TPA. Strong TPA, with a cross section value as high as 2100 GM at an excitation wavelength of 770 nm is found in acetophenone which is a solvent of intermediate polarity. The TPA spectra were also reproduced using a sum over states three-state model. A study of the TPA induced photobleaching of the fluorene molecule, doped in a solid poly(methyl-methacrylate) film, has shown that this material is very promising for efficient TPA optical data storage.     

From Graftable Biphotonic Chromophores to Water‐Soluble Organic Nanodots for Biophotonics: The Importance of Environmental Effects

The photophysical and two‐photon absorption (TPA) properties of biphotonic chromophores with one or two phenol pendant units were studied and compared with that of a model biphotonic quadrupolar chromophore. A water‐soluble dendritic structure was then synthesized by using the pendant moieties as starting points for the construction of dendritic branches. We show that the polarity of the environment significantly modulates both the fluorescence and the TPA responses of the different chromophoric derivatives. This extends to more subtle effects that involve phenol pendant moieties that were found to act as discrete solvating units and to modify both the photophysics and the TPA response of the chromophore. This demonstrates the high sensitivity of the TPA response of quadrupolar derivatives to minute alterations in the environment. Moreover, the dendritic branches were found to behave as a peculiar cybotactic environment that was able to tune the fluorescence and TPA response of the inner chromophore by creating a polar environment. This reveals a new direction for exploiting such effects by playing on the dendritic architecture (e.g., the nature and shape of the building blocks, the geometry and position of the chromophore) to modulate the TPA responses.     

Ultrafast dynamics in multibranched structures with enhanced two-photon absorption

The understanding of the mechanism of the enhanced two-photon absorption (TPA) in multibranched chromophore systems is of importance to the design of materials with the large TPA cross-sections and for future applications. In this communication, the mechanism of enhanced TPA properties is investigated. For a dendritic model system, the excited-state dynamics for both population (T1-process) and phase relaxation (T2-process) processes involved are investigated by a combination of time-resolved spectroscopic techniques. The results of time-resolved fluorescence anisotropy are compared with previous results obtained from other branched chromophore systems. It is found that the PRL-701 trimer system, which possesses the large enhancement of two-photon absorption cross-section, gives a faster anisotropy decay (fluorescence upconversion and transient absorption), a longer population relaxation time (fluorescence lifetime), and a weaker coupling to the solvent (a larger photon echo peak shift initial value). New strategies for rational design of large TPA materials can be achieved based on a better understanding of the mechanism of the enhancement.     

氧芴三苯胺多枝分子的双光子吸收与电化学行为

研究了3个氧芴/三苯胺衍生物: E-2,8-双(4-二苯胺基苯乙烯基)氧芴(简称OT-G1)、E-2,8-双[4-(二苯基氨基-二苯乙烯基)(4’-溴苯基)氨基-苯乙烯基]氧芴(简称OT-G1.5)和E-2,8-双-[4’,4″-二-(二苯胺基苯乙烯基)-4-二苯胺基苯乙烯基]氧芴(简称OT-G2)的双光子吸收和电化学行为. 研究结果表明, 分子“代数”从1→1.5→2增高, 氧芴三苯胺多枝分子的HOMO能级升高、双光子荧光强度和双光子吸收截面明显增大. 由于HOMO能级的升高有利于分子的电荷转移, 因而分子表现出强的双光子吸收能力, 这表明可通过电化学行为来推断出分子的双光子吸收性能.     

Two-photon excitation of substituted enediynes

Electronic spectroscopy of nine benzannelated enediynes and a related fulvene was studied under one-photon and two-photon excitation conditions. We utilize measured absorbance and emission spectra and time-resolved fluorescence decays of these molecules to calculate their radiative lifetimes and fluorescence quantum yields. The fluorescence quantum yields for the other compounds were referenced to the fluorescence quantum yield of compound 3 and used to determine relative two-photon absorption cross-sections. Further insight into experimental studies has been achieved using time-dependent density functional (TD-DFT) computations. The probability of two-photon absorption (TPA) increases noticeably for excitation to the higher excited states. The photophysical properties of benzannelated enediynes are sensitive to substitutions at both the core and the periphery of the enediyne chromophore. Considerably enhanced two-photon absorption is observed in an enediyne with donor substitution in the middle and acceptor substitution at the termini. Excited states with B symmetry are not active in TPA spectra. From a practical point of view, this study extends the range of wavelengths applicable for activation of the enediyne moiety from 350 to 600 nm and provides a rational basis for future studies in this field. Our theoretical computations confirmed that lowest energy TPA in benzannelated enediynes involves different orbitals than lowest energy one-photon absorbance and provided further support to the notion that introduction of donor and acceptor substituents at different ends of a molecule increases TPA.     

外围带咔唑基的联苯桥联二聚对苯乙烯撑的双光子吸收性能

报道了十字形结构对荧光生色团的双光子吸收(TPA)作用横截面积的影响. 1,4-二(9'-乙基咔唑基)- 3'-乙烯基苯(R1)是经典的具有D-π-D结构的TPA生色团. 通过一个联苯桥将两个双光吸引(TPA)链连接在一起得到的十字形分子(1)显示出比单链分子明显增大的双光子吸收作用横截面积(σ'). 在10-4 mol/L 的甲苯溶液中, 十字结构分子1的σ'值为491.0×10-50 cm4·s, 而R1的σ'值仅为137.5×10-50 cm4·s. σ'的放大可以归结为十字结构使TPA 生色团的偶极呈交叉排列, 抑制了浓溶液中的荧光猝灭.     

Synthesis,Photophysical Properties of Tribranched Chromophores Based on 1,3,5‐Triazine Core and Different Electro‐donating End‐groups

Three two‐photon absorption (TPA) tribranched chromophores were successfully prepared, in which 1,3,5‐triazine is been as electron deficient core, 1,4‐phenylenedivinylene as conjugated bridge, 3,4‐ethylenedioxythiophene (EDOT) ( T1 ), N‐methylpyrrole ( T2 ) or triphenylamine ( T3 ) as electron‐donating end‐groups. Their photophysical properties were studied by absorption, one‐ and two‐photon fluorescence and TPA cross‐section determination. The nonlinear transmission (NLT) measurement in femtoseconds (fs) regime at 800 nm indicates that TPA cross‐section (₂ values of T1 , T2 and T3 with extended Π‐conjugated bridge are much larger than the corresponding chromophore T4 with a short length bridge, and TPA cross‐section of T1 with end‐groups EDOT exhibits a remarkable enhancement compared with T2 and T3 having the same length Π‐system. The chromophores T1 , T2 and T3 show also remarkable up‐converted luminescence and optical limiting activity.     

以N为耦合中心多枝分子的双光子上转换荧光

采用非线性透过率法研究了以N为耦合中心的多枝化合物N-[4-{2-(3,5-二-[5-(4-叔丁基苯基)-1,3,4-噁二唑-2-]苯基}-1-乙烯基}苯基}-N,N-二苯胺(BPODPA), N,N-双[4-{2-(3,5-二-[5-(4-叔丁基苯基)-1,3,4-噁二唑-2-]苯基}-1-乙烯基}苯基}-N-苯胺(BBPOPA)和N,N,N-三[4-{2-(3,5-二-[5-(4-叔丁基苯基)-1,3,4-噁二唑-2]苯基}-1-乙烯基}苯基}胺(TBPOA)的双光子吸收性质, 测定了化合物的单光子荧光光谱和双光子上转换荧光光谱, 研究了多枝化对三苯胺分子双光子吸收和双光子激发荧光性质的影响.在800 nm波长的激光激发下,化合物BPODPA、BBPOPA和TBPOA在二氯甲烷溶液中发出很强的蓝绿色双光子上转换荧光, 荧光峰分别位于502、515 和518 nm. 这些多枝结构化合物的双光子吸收截面较大, 双光子吸收增强来源于多枝分子中扩展的π共轭体系和重复单元的协同效应.     

Water‐Soluble Triarylborane Chromophores for One‐ and Two‐Photon Excited Fluorescence Imaging of Mitochondria in Cells

Three water‐soluble tetracationic quadrupolar chromophores comprising two three‐coordinate boron π‐acceptor groups bridged by thiophene‐containing moieties were synthesised for biological imaging applications. Compound 3 containing the bulkier 5‐(3,5‐Me₂C₆H₂)‐2,2′‐(C₄H₂S)₂‐5′‐(3,5‐Me₂C₆H₂) bridge is stable over a long period of time, exhibits a high fluorescence quantum yield and strong one‐ and two‐photon absorption (TPA), and has a TPA cross section of 268 GM at 800 nm in water. Confocal laser scanning fluorescence microscopy studies in live cells indicated localisation of the chromophore at the mitochondria; moreover, cytotoxicity measurements proved biocompatibility. Thus, chromophore 3 has excellent potential for one‐ and two‐photon‐excited fluorescence imaging of mitochondrial function in cells.     

Hidden electronic excited state of enhanced green fluorescent protein

Precise two-photon absorption spectra of the green fluorescent protein (GFP) and the mutants sapphire-GFP (T203I) and enhanced GFP (S65T/F64L), as well as a model compound for the chromophore, 4'-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI) were measured by multiplex two-photon absorption spectroscopy. The observed TPA bands of the anionic forms of enhanced GFP and HBDI were significantly shifted to the higher energy compared with the lowest-energy bands in one-photon absorption spectra. This result indicated the existence of a hidden electronic excited state in the vicinity of the lowest excited singlet (S1) state of the anionic form of the GFP chromophore, which is the origin of the blue shift of the two-photon absorption spectra as well as two-photon fluorescence excitation spectra.     

一个新的具有大的吸收截面的双光子引发剂的合成和非线性光学性质

E,E-1,4-Bis（4＇-N,N-diphenylaminostyryl）-2,5-dimethoxybenzene （DPAMOB） has been synthesized by a simple and effective solid phase Wittig reaction and characterized by 1^H NMR spectra and elemental analysis, Linear absorption, single-photon induced fluorescence and two-photon induced fluorescence spectra were experimentally studied. The new dye has a large two-photon absorption （TPA） cross-section of σr= 1007,2 GM [1 GM= 1 × 10^-50 cm^4·s/（photon molecule）] at 800 nm measured by the two-photon induced fluorescence method. The experimental results confirm that DPAMOB is a good TPA chromophore and can successfully initiate two-photon photopolymerization of ethoxylated trimethylolpropane triacrylate esters （SR454）. Finally, a microstructure has been fabricated by use of DPAMOB as initiator.     

Fusing three perylenebisimide branches and a truxene core into a star-shaped chromophore with strong two-photon excited fluorescence and high photostability

A novel star-shaped chromophore, Tr-PBI, was constructed by fusing three perylenebisimide branches and a truxene core. Tr-PBI exhibits high photostability and excellent two-photon properties: the maximum of δ(TPA) is 11,000 GM at 990 nm and fluorescence quantum efficiency Φ is 0.40 in THF.     

Synthesis and Nonlinear Optical Properties of a New A-π-A Two-Photon Compound Utilizing Dibenzothiophene as Center

A new two‐photon material, 3E,6E‐bis(2‐pyrid‐4′‐ylvinyl)dibenzothiophene (BPVDBT), has been firstly synthesized by an efficient Pd‐catalyzed Heck coupling route. The single‐ and two‐photon fluorescence, quantum yields, lifetimes, solvent effects of the chromophore were studied in detail and the compound exhibited solvent‐sensitivity. The fluorescence intensity (I_out) and input excitation intensity (I_in) can fit in well with the quadratic parabolas, which indicates that the up‐converted fluorescence was induced by the two‐photon absorption (TPA). TPA cross‐section of BPVDBT has been measured using the two‐photon‐induced fluorescence method, whose value is 14.24×10^?50 cm⁴·s·photon^?1·molecule^?1 at 750 nm. The experimental results confirm that BPVDBT is a good two‐photon absorbing chromophore with an A‐π‐A type.     

POLARIZED PHOTO ACOUSTIC SPECTRA OF PHYCOBILISOMES IN POLYVINYL ALCOHOL FILMS

Abstract— Phycobilisomes from Porphyridium cruentum , suspended in polyvinyl alcohol were found to be highly stable, and had normal absorption and fluorescence spectra. Intact phycobilisomes had a major emission peak at 680 nm, whereas upon partial dissociating the major emission was at 580 nm. Incorporation of phycobilisomes in thin polyvinyl alcohol films facilitated examination by photoacoustic spectroscopy. The photoacoustic spectra had a broad absorption maximum at 545–565 nm (phycoerythrin), which resolved as two peaks (545 and 563 nm) in absorption spectra. Stretching of films resulted in apparent chromophore reorientation in partially dissociated, but not in intact phycobilisomes. Only in dissociated phycobilisomes was observed a differential chromophore orientation at 685 nm by polarized fluorescence, which is attributed to a change in orientation of the terminal phycobilisome pigment relative to phycoerythrin.     

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.     

含有三苯胺单元的萘酰亚胺化合物的合成及其荧光调控研究

通过在1,8-萘酰亚胺发光单元上引入三苯胺单元, 合成了含三苯胺单元的萘酰亚胺化合物(TNP和TNM). 吸收光谱、稳态及瞬态的荧光光谱证实了该体系不仅存在着Förster-type单线态能量转移, 同时存在着光诱导电荷转移(PIET), 正是由于PIET导致目标化合物TNP和TNM的荧光发生严重淬灭, 其淬灭超过99%. 通过加入酸将三苯胺中心氮原子进行质子化, 切断其PIET过程, 可实现荧光的淬灭与恢复的可逆性荧光调控. 该体系的荧光切断与恢复的过程可用于荧光开关的设计.     

Evidence for the isomerization and decarboxylation in the photoconversion of the red fluorescent protein DsRed

Recently, it has been shown that the red fluorescent protein DsRed undergoes photoconversion on intense irradiation, but the mechanism of the conversion has not yet been elucidated. Upon irradiation with a nanosecond-pulsed laser at 532 nm, the chromophore of DsRed absorbing at 559 nm and emitting at 583 nm (R form) converts into a super red (SR) form absorbing at 574 nm and emitting at 595 nm. This conversion leads to a significant change in the fluorescence quantum yield from 0.7 to 0.01. Here we demonstrate that the photoconversion is the result of structural changes of the chromophore and one amino acid. Absorption, fluorescence, and vibrational spectroscopy as well as mass spectrometry suggest that a cis-to-trans isomerization of the chromophore and decarboxylation of a glutamate (E215) take place upon irradiation to form SR. At the same time, another photoproduct (B) with an absorption maximum at 386 nm appears upon irradiation. This species is assigned as a protonated form of the DsRed chromophore. It might be a mixture of several protonated DsRed forms as there is at least two ways of formation. Furthermore, the photoconversion of DsRed is proven to occur through a consecutive two-photon absorption process. Our results demonstrate the importance of the chromophore conformation in the ground state on the brightness of the protein as well as the importance of the photon flux to control/avoid the photoconversion process.     

利用聚合物自组装实现绿色荧光蛋白生色团的荧光增强

根据绿色荧光蛋白的发光原理,采用聚乙二醇与聚甲基丙烯酸甲酯的两亲性两嵌段聚合物通过自组装包覆生色团的方式,模拟了绿色荧光蛋白发光,考察了组装行为对光学性能的影响,并将其用于细胞成像.通过核磁共振、高分辨质谱、傅里叶变换红外光谱、凝胶渗透色谱、紫外-可见吸收光谱及荧光光谱等表征了生色团分子和聚合物的结构及性能.生色团紫外最大吸收在371 nm,荧光最大发射峰在428 nm.聚合物和生色团进行组装后,其紫外吸收消失,而最大荧光发射峰强度大大增强,且发生了约70 nm的红移,这是因为组装使得生色团的自由旋转受到了限制,且生色团共平面性增加.动态光散射(DLS)和透射电镜(TEM)证明了纳米粒子的结构和尺寸.由于尺寸适合且具有较好的荧光性能,纳米粒子成功应用于细胞成像.这种绿色荧光蛋白生色团的简单自组装方式在生物成像领域具有良好应用前景.     

Experimental and Theoretical Studies of Quadrupolar Oligothiophene‐Cored Chromophores Containing Dimesitylboryl Moieties as π‐Accepting End‐Groups: Syntheses,Structures, Fluorescence,and One‐ and Two‐Photon Absorption

Quadrupolar oligothiophene chromophores composed of four to five thiophene rings with two terminal (E)‐dimesitylborylvinyl groups ( 4 V – 5 V ), and five thiophene rings with two terminal aryldimesitylboryl groups ( 5 B ), as well as an analogue of 5 V with a central EDOT ring ( 5 VE ), have been synthesized via Pd‐catalyzed cross‐coupling reactions in high yields (66–89 %). Crystal structures of 4 V , 5 B , bithiophene 2 V , and five thiophene‐derived intermediates are reported. Chromophores 4 V , 5 V , 5 B and 5 VE have photoluminescence quantum yields of 0.26–0.29, which are higher than those of the shorter analogues 1 V – 3 V (0.01–0.20), and short fluorescence lifetimes (0.50–1.05 ns). Two‐photon absorption (TPA) spectra have been measured for 2 V – 5 V , 5 B and 5 VE in the range 750–920 nm. The measured TPA cross‐sections for the series 2 V – 5 V increase steadily with length up to a maximum of 1930 GM. We compare the TPA properties of 2 V – 5 V with the related compounds 5 B and 5 VE , giving insight into the structure–property relationship for this class of chromophore. DFT and TD‐DFT results, including calculated TPA spectra, complement the experimental findings and contribute to their interpretation. A comparison to other related thiophene and dimesitylboryl compounds indicates that our design strategy is promising for the synthesis of efficient dyes for two‐photon‐excited fluorescence applications.     

PHOTOREACTIVATING ENZYME FROM STREPTOMYCES GRISEUS—III. EVIDENCE FOR THE PRESENCE OF AN INTRINSIC CHROMOPHORE

Evidence is presented that DNA photoreactivating enzyme from Streptomyces griseus consists of a high molecular protein part and a low molecular chromophore which is released by denaturation. The free chromophore is highly fluorescent and has an absorption maximum at 420 nm. In native photoreactivating enzyme the chromophore fluorescence is almost completely quenched and there is an additional absorption band at 445 nm. Native photoreactivating enzyme spontaneously looses its chromophore following first order kinetics as measured by the increase of fluorescence intensity. A good correlation was found between the increase of fluorescence intensity and the decrease of biological activity, stressing the importance of the chromophore-protein bond. The presence of DNA greatly retards the spontaneous release of chromophore, and with UV-irradiated DNA the photoreactivating enzyme is almost completely stable. In five different chromatographic systems, cochromatography of biological activity and enzyme-bound chromophore was found, thus ruling out the possibility that the observed chromophore belongs to a contamination in the enzyme preparation. Photoreactivating enzyme binds very strongly to Blue-Sepharose indicating the presence of a positive charge in the polynucleotide binding site.