Multichromophoric π‐Conjugation: Modular Design for Gated and Cascade Energy Transfer

Multichromophore arrays allow for cascade energy transfer. As an isoelectronic analogue of indacenyl, bis(triazolo)benzene features a fused tricyclic skeleton that rigidly places two π‐extended triazoles in close proximity. Such triazole‐based fluorophores behave as electronically independent modules in the ground states, but become tightly coupled upon photoexcitation for highly efficient excitation energy transfer (EET) that can be gated by external stimuli. Taking this donor–acceptor fluorophore system a step further, we have designed and implemented a cascade EET. Here, the initial excitation takes part in a circular relay to arrive at the longest‐wavelength emitting site as the final destination. Modularly constructed triazoloarenes should serve as versatile platforms for chemically controlled optical signaling.     

Synthesis of Symmetrical Multichromophoric Bodipy Dyes and Their Facile Transformation into Energy Transfer Cassettes

Multichromophoric boron‐dipyrromethene (Bodipy) dyes synthesized on phenylene‐ethynylene platforms have been be converted to energy transfer cassettes in a one‐step chemical transformation. Excitation energy transfer processes in these highly symmetrical derivatives were studied in detail, including time‐resolved fluorescence spectroscopy techniques. Excitation spectra and the emission lifetimes suggest efficient energy transfer between the donor and acceptor chromophore. These novel energy transfer cassettes, while highlighting a short‐cut approach to similar energy transfer systems, could be useful as large pseudo‐Stokes shift multichromophoric dyes with potential applications in diverse applications.     

Remote Sensitized Photoisomerization via Through‐Bond Triplet–Triplet Energy Transfer Mediated by a Salt Bridge in a Supramolecular Dyad

A supramolecular dyad, BP‐(amidinium‐carboxylate)‐NBD is constructed, in which benzophenone (BP) and norbornadiene (NBD) are connected via an amidinium‐carboxylate salt bridge. The photophysical and photochemical properties of the assembled BP‐(amidinium‐carboxylate)‐NBD dyad are examined. The phosphorescence of the BP chromophore is efficiently quenched by the NBD group in BP‐(amidinium‐carboxylate)‐NBD via the salt bridge. Time‐resolved spectroscopy measurements indicate that the lifetime of the BP triplet state in BP‐(amidinium‐carboxylate)‐NBD is shortened due to the quenching by the NBD group. Selective excitation of the BP chromophore results in isomerization of the NBD group to quadricyclane (QC). All of these observations suggest that the triplet–triplet energy transfer occurs efficiently in the BP‐(amidinium‐carboxylate)‐NBD salt bridge system. The triplet–triplet energy transfer process proceeds with efficiencies of approximately 0.87, 0.98 and the rate constants 1.8×10³ s^?1, and 1.3×10⁷ s^?1 at 77 K and room temperature, respectively. The mechanism for the triplet–triplet energy transfer is proposed to proceed via a “through‐bond” electron exchange process, and the non‐covalent bonds amidinium‐carboxylate salt bridge can mediate the triplet–triplet energy transfer process effectively for photochemical conversion.     

Delayed Fluorescent Emission from Pyrene Doped Phenanthrene Nanoparticles Based on Triplet-triplet Energy Transfer

Doped nanoparticles were prepared from pyrene and phenanthrene using a facile reprecipitation method. The doped nanoparticles presented unique delayed fluorescent emissions of pyrene under the unprotected condition. The ratio of the intensity of delayed fluorescence (I_DF) to that of phosphorescence (I_P) is about 4:1, which almost keeps unchanged with the decrease of pyrene content at room temperature. The intensity of the delayed fluorescence emissions is dependent on the relative content of pyrene, as well as the aggregation degree of nanoparticles. The delayed emissions are contributed to efficient triplet‐triplet energy transfer from phenanthrene (donor) to pyrene (acceptor). Steady fluorescence measurement have proved that the singlet‐singlet energy transfer process was also existent dominated by the radiation energy transfer mechanism.     

Excitation Energy Transfer in Dendritic Host–Guest Donor–Acceptor Systems

We report on a study of a physically formed host–guest system, which was designed to be investigated by fluorescence energy transfer. All donor and acceptor molecules used were cyanine dyes. Investigation was performed at the ensemble level as well as at the single‐molecule level. The ensemble measurements revealed a distribution of binding sites as well for the donor as for the acceptor. Accordingly, we found a distribution of the energy transfer efficiency. At the single‐molecule level, these distributions are still present. We could discriminate entities that show very efficient energy transfer, some that do not show any energy transfer and systems whose energy transfer efficiency is only about 50 %. The latter allowed the time‐resolved detection of energy transfer of single entities through the acceptor decay. Finally, we discuss the observation that the energy transfer efficiency fluctuates as a function of time.     

Synthesis and Photophysical Properties of Multichromophoric Carbonyl‐Bridged Triarylamines

The synthesis and photophysical properties of two novel multichromophoric compounds is presented. Their molecular design comprises a carbonyl‐bridged triarylamine core and either naphthalimides or 4‐(5‐hexyl‐2,2′‐bithiophene)naphthalimides as second chromophore in the periphery. The lateral chromophores are attached to the core via an amide linkage and a short alkyl spacer. The synthetic approach demonstrates a straightforward functionalization strategy for carbonyl‐bridged triarylamines. Steady‐state and time‐resolved spectroscopic investigations of these compounds, in combination with three reference compounds, provide clear evidence for energy transfer in both multichromophoric compounds. The direction of the energy transfer depends on the lateral chromophore used. Furthermore, the compound bearing the lateral 4‐(bithiophene)naphthaimides is capable of forming fluorescent gels at very low concentrations in the sub‐millimolar regime whilst retaining its energy transfer properties.     

合成双分子膜多元体系的激发态能量转移

发现在４－（４－癸氧基联苯－４－氧基三甲基）溴化铵双分子膜体系内，从联苯给体通过结合在膜表面上的达旦黄传递到罗丹明Ｂ受体的三元激发态的能量转移效率较高．探讨了囊泡在此能量转移过程中的特殊功能作用和能量转移的机制．同时还观察到了在此体系内通过静电相互作用，组织在囊泡表面上的达旦黄、荧光黄、罗丹明Ｂ和四苯基卟啉间的多元能量转移，这种能量转移可改善光的输出，扩展光波的覆盖范围．     

Photoisomerization of norbornadiene group in a rigid bichromophoric compound initiated by remote keto chromophore: long-distance through-bond triplet energy transfer

A diad compound 3β(bicyclo[2,2,1]hepta-2,5-diene-2-methylcarboxylate-3-carboxy)-an-drost-5-en-17-one (NBD-S-ONE) was synthesized and its photochemistry was examined. Irradiation of NBD-S-ONE in acetonitrile at λ > 300 nm selectively excited the keto chromophore. After intersystem crossing, the triplet energy of the keto group was transferred to the NBD group with 18.6% efficiency via a through-bond mechanism, resulting in the isomerization of the latter group to the quadricyclane group.     

Excitation Energy Transfer and Exchange-Mediated Quartet State Formation in Porphyrin-Trityl Systems

Photogenerated multi-spin systems hold great promise for a range of technological applications in various fields, including molecular spintronics and artificial photosynthesis. However, the further development of these applications, via targeted design of materials with specific magnetic properties, currently still suffers from a lack of understanding of the factors influencing the underlying excited state dynamics and mechanisms on a molecular level. In particular, systematic studies, making use of different techniques to obtain complementary information, are largely missing. This work investigates the photophysics and magnetic properties of a series of three covalently-linked porphyrin-trityl compounds, bridged by a phenyl spacer. By combining the results from femtosecond transient absorption and electron paramagnetic resonance spectroscopies, we determine the efficiencies of the competing excited state reaction pathways and characterise the magnetic properties of the individual spin states, formed by the interaction between the chromophore triplet and the stable radical. The differences observed for the three investigated compounds are rationalised in the context of available theoretical models and the implications of the results of this study for the design of a molecular system with an improved intersystem crossing efficiency are discussed.     

Competitive Excimer Formation and Energy Transfer in Zr‐Based Heterolinker Metal–Organic Frameworks

The spectroscopy and dynamics of a series of Zr‐based MOFs in dichloromethane suspension are reported. These Zr‐NADC MOFs were constructed by using different mixtures of 2,6‐naphthalenedicarboxylate (NDC) and 4‐amino‐2,6‐naphthalenedicarboxylate (NADC) as organic linkers. The fraction of NADC relative to NDC in these heterolinker MOFs ranges from 2 to 35 %. The results indicate two competitive photoprocesses: NDC excimer formation and an energy transfer (ET) from excited NDC linkers to NADC linkers. Increasing the fraction of NADC linkers in the Zr‐NADC nanostructure decreases the mean time constant of NDC excimer formation, while the NADC emission intensity experiences a drop at the highest fraction of this linker in the MOF. The first observation is explained by an increase in the energy‐transfer probability between the two linkers, and the second by emission quenching in the NADC linkers due to ultrafast charge transfer assisted by the amino group. Femtosecond time‐resolved emission studies showed that the ET process (recorded as decaying and rising components) from excited NDC to NADC takes place in 1.2 ps. Direct excitation of the NADC linkers (at 410 nm) shows a decaying, but not rising, component of 250–480 fs, which could reflect the formation of a nonemissive charge‐separation state. The results show that by using MOFs having heterolinkers it is possible to trigger and tune excimer formation and ET processes.     

基于激发态能量转移机理比率型荧光探针的研究进展

激发态能量转移(Excitation Energy Transfer,EET)作为一类重要的光物理现象,被广泛用于比率型荧光探针和分子灯标的设计以及DNA检测等多个领域.影响EET效率的两个重要因素是供受体间的空间距离和光谱交盖,通过调节供受体间的空间距离或光谱重叠程度来调控能量转移过程,实现对目标客体的双波长比率检测.综述了基于不同供受体荧光团的EET体系、供受体间的连接方式对能量转移效率的影响,以及通过调控供受体间光谱重叠程度或空间距离,获得识别不同客体的比率型荧光探针,并对EET机理的比率型荧光探针的设计以及未来在生物成像和医学检测等领域的应用进行了展望.     

基于共振能量转移的生物传感器在食品安全检测中的应用研究进展

共振能量转移(Resonance energy transfer,RET)是一种发生在供体和受体之间的非辐射能量转移过程。RET的能量转移效率对供体和受体间的距离变化非常敏感,可被用于开发新型的光学生物传感器。与传统光学生物传感器相比,基于RET的生物传感器无需洗涤及分离过量标记物等步骤,可大幅简化检测流程。因RET具有灵敏度高、操作简便及速度快等优点,近年来,在医学诊断、生命科学研究、环境监控以及食品安全检测等领域备受关注。该文根据能量供体的不同,将RET分为3种类型：荧光共振能量转移(Fluorescence resonance energy transfer,FRET)、生物发光共振能量转移(Bioluminescence resonance energy transfer,BRET)和化学发光共振能量转移(Chemiluminescence resonance energy transfer,CRET)。并分别对基于上述3种RET类型的生物传感器在食品安全检测中的应用研究进展进行了综述,同时对其应用前景和发展趋势进行了展望。     

Progresses of Single Molecular Fluorescence Resonance Energy Transfer in Studying Biomacromolecule Dynamic Process

Biomacromolecules participate in various kinds of vital processes. Observing and analyzing their structural dynamic and the dynamic processes of intermolecular interaction at molecular level are important for understanding the action mechanism. Since its advent, single molecular fluorescence resonance energy transfer (SM-FRET) has demonstrated its great potential in studying conformational change and interaction process of biomacromolecules, and a series of new mechanisms have been revealed. This review summarized recent progresses of SM-FRET in studying protein structural dynamic, nucleic acid structural dynamic, protein-protein and protein-nucleic acid interactions.     

Characterization of the Mode of Incorporation of Lipophilic Compounds in Solid Dispersions at the Nanoscale Using Fluorescence Resonance Energy Transfer (FRET)

Summary: Efficient engineering of solid dispersions stagnates by the current inability to establish the mode of drug distribution on a molecular level at a low drug load. This study describes the application of fluorescence resonance energy transfer (FRET) to characterize the mode of incorporation of dispersed lipophilic molecules in a solid matrix. Two different lipophilic fluorophores (donor and acceptor) were used as model substances and were incorporated in polyvinylpyrrolidone to form solid dispersions using two different production processes: lyophilization and fusion. The efficiency of the resonance energy transfer from donor to acceptor was measured by confocal microscopy. We show that the method can be used to compare the modes of drug incorporation of solid dispersions at the nanoscale.

Absorption and emission spectra of Bodipy R6G (donor) and Bodipy 650/665 (acceptor).     

Homogeneous Detection of Trypsin in Protein Mixtures Based on Fluorescence Resonance Energy Transfer between Anionic Conjugated Polymer and Fluorescent Probe

Herein we describe a novel and simple conjugated polymer‐fluorescent probe based platform for trypsin detection from protein mixtures in homogeneous solution. This platform takes advantage of specific interaction between the probe and the active site of trypsin and the electrostatic interaction between the polymer and the protein to mediate energy transfer between the polymer and the probe. This method does not require any separation steps, which should facilitate high‐throughput protease screening and drug discovery.

     

Enhancement of Förster Energy Transfer within a Microspherical Cavity

Energy transfer from pyrene to perylene molecules co-doped within a poly(methyl methacrylate) latex microsphere was drastically accelerated relative to free space. Fluorescence spectra of the microspheres showed that the relative emission intensities of pyrene and perylene changed with the sphere diameter. Analyses of emission decay profiles clarified that F?rster-type energy-transfer processes were induced and that the transfer rates increased within the microspherical cavity. This enhancement can be ascribed not only to the quantum electrodynamic effects on the pyrene emission rate, but also the cavity effect of increasing the overlapping factor between donor emission and acceptor absorption spectra.     

刚性溶液中分子间能量传递的研究

本文应用了荧光光谱和时间分辨的荧光光谱技术研究了1,4-二苯乙烯基苯(给体)与吖啶黄(受体)在乙醇的刚性溶液中分子间能量传递的行为,探讨了分子的浓度、给体、受体分子间的实际距离 R、临界距离 R_0与能量传递效率 E_T、能量传递速率常数 K_T 之间的关系。     

Ultrafast Nonadiabatic Photoisomerization Dynamics Mechanism for the UV Photoprotection of Stilbenoids in Grape Skin

Natural UV photoprotection plays a vital role in physiological protection. It has been reported that UVC radiation can make resveratrol (RSV) and piceatannol (PIC) accumulate in grape skin. In this work, we demonstrated that RSV and PIC could significantly absorb UVA and UVB, and confirmed their satisfactory photostability. Furthermore, we clarified the UV photoprotection mechanism of typical stilbenoids of RSV and PIC for the first time by using combined femtosecond transient absorption (FTA) spectroscopy and time‐dependent density functional theory (TD‐DFT) calculations. RSV and PIC can be photoexcited to the excited state after UVA and UVB absorption. Subsequently, the photoisomerized RSV and PIC quickly relax to the ground state via nonadiabatic transition from the S₁ state at a conical intersection (CI) position between potential energy surfaces (PESs) of S₁ and S₀ states. This ultrafast trans‐cis photoisomerization will take place within a few tens of picoseconds. As a result, the UV energy absorbed by RSV and PIC could be dissipated by an ultrafast nonadiabatic photoisomerization process.     

稀土配合物发光中的能量传递研究

就稀土发光的能量传递开展了3个方面的初步研究。首先,研究了稀土镧和铕掺杂后共发光的现象和机制;其次是研究了稀土铽配合物作为能量传递桥可以将能量从导电高分子聚乙烯咔唑（PVK）有效地传递给铕配合物;第三,发现通过物理掺杂的方法可以改变稀土铕配合物的激发光谱的形状,使其向着长波长方向移动,这样可以使铕配合物的激发光谱和PVK的发射光谱发生更大的重叠,从而增强它们之间的能量传递效率。