三分子激基复合物的研究

本文证实了苊与1,4-二氰基苯(DCB)可以形成激基复合物,同时当苊的浓度较大时,也可以生成三分子的激基复合物。此外还证明了聚苊可以生成非相邻的激基缔合物,聚苊与DCB也可以生成三分子激基复合物。通过光物理过程的动力学推导,证明在聚苊体系中,先生成(DA)^*,然后再形成(DDA)^*三分子激基复合物。     

N-n-butyl-N,N-di(2-naphthylmethyl)amine: A compound exhibiting intramolecular excimer and exciplex formation

The dinaphthylamine (3) is unique in that it exhibits both intramolecular excimer and exciplex formation. The relative amounts of each is dependent upon the solvent polarity. Highly polar solvents, e.g. methanol, lead to the emission being entirely that of the exciplex but addition of acid to these solutions prevents exciplex formation and only excimer is observed.     

激基缔合物和激基复合物的形成及溶剂效应的研究

测试了ω-对联苯基多亚甲基羧酸4-[5′-对联苯基-1,3,4-(口恶)二唑基-2′-]苄酯及其模型化合物2-对甲苯基-5-联苯基-1,3,4-,(口恶)二唑在不同极性溶剂中的荧光发射光谱。它们既能形成分子间的激基缔合物又能形成分子内的激基复合物和三分子激基复合物。实验结果表明,溶剂极性的增加,有利于分子内激基复合物和三分子激基复合物的形成。     

N,N′-双-β-萘甲基哌嗪分子内激发态复合物形成的混合溶剂效应

本文测定了N,N′-双-β-萘甲基哌嗪(DMNP)在苯与乙腈混合溶剂中的荧光光谱。在乙腈含量<5(mol·dm^-3)时,乙腈猝灭DMNP苯溶液的荧光符合Stern-Volmer方程,表明极性溶剂分子乙腈与DMNP分子内激基复合物存在着相互作用。随着乙腈含量的增加,DMNP分子内激基复合物(exci-plex)荧光的猝灭与红移以及分子内激基缔合物(excimer)的逐步形成则仅与体系的极性有关。文中还讨论了DMNP激发态复合物形成的机理。     

Intramolecular exciplex and intermolecular excimer formation of 1,8-naphthalimide-linker-phenothiazine dyads

Steady-state fluorescence spectra were measured for 1,8-naphthahlimide-linker-phenothiazine dyads (NI-L-PTZ, where L = octamethylenyl ((CH2)8) and 3,6,9-trioxaundecyl ((CH2CH2O)3C2H4)), NI-C8-PTZ and NI-O-PTZ, as well as the NI derivatives substituted on the nitrogen atom with various linker groups without PTZ as the reference NI molecule in n-hexane. Normal fluorescence peaks were observed at 367-369 nm in all NI molecules together with a broader emission around 470 nm, which is assigned to the excimer emission between the NI in the singlet excited state (1NI*) and the NI moiety of another NI molecule (1[NI/NI]*). In addition, a broad peak around 600 nm was observed only for NI-L-PTZ, which is assigned to an intramolecular exciplex emission between donor (PTZ) and acceptor (NI) moieties in the excited singlet state, 1[NI-L-NI]*. The formation of an intramolecular exciplex corresponds to the existence of a conformer with a weak face-to-face interaction between the NI and PTZ moieties in the excited state because of the long and flexible linkers. The excited-state dynamics of the NI molecules in n-hexane were established by means of time-resolved fluorescence spectroscopy.     

Photophysical processes of a copolymer containing naphthalene and carbazole rings

The photophysical processes of copolymer formed by copolymerization of beta-naphthyl-methacrylate (NMA) with vinylcarbazole (VCZ) were studied. The results show that when the solution of copolymer (NMA-VCZ) in THF is located in a low concentration range (about 10(-8) mol/l), the fluorescence emission is in good agreement with that of NMA monomer and the excimer is formed with gradual increase in concentration of copolymer (NMA-VCZ). The fluorescence of copolymer (NMA-VCZ) can be efficiently quenched both by electron donors and acceptors where the quenching effects follow the Stern-Volmer equation. The dimolecular exciplex between copolymer (NMA-VCZ) and N,N-dimethylaniline (DMA) is formed and the triple exciplex is also observed in the same system.     

Photoluminescent mechanism of a proton-transfer laser dye in highly doped polymer films

Photoluminescent properties in thin films of the proton-transfer laser dye, 2-(2-hydroxyphenyl)benzothiazole (HBT) were investigated, when it was doped into hole-transport polymer, poly(N-vinylcarbazole) and when it was codoped with hole-transport small molecule, N,N′-di(m-tolyl)-N,N′-diphenylbenzidine (TPD) into polystyrene. The more the doping concentration of HBT was raised up to about 40 wt%, the more its photoluminescent intensity was enhanced without showing excimer or exciplex emissions. The mechanism for such phenomena was discussed in connection with the excited-state intramolecular proton-transfer reaction of HBT.     

双-β-萘甲基二胺及其衍生物的荧光光谱及分子内激发态复合物的形成

我们合成了N,N'-二甲基-二-β-萘甲基乙二胺(Ⅰ),N,N'-二甲基-二-β-萘甲基丙二胺(Ⅱ),N,N'-二-β-萘甲基哌嗪(Ⅲ)三个化合物,并测定了它们的荧光光谱。结果表明,它们既能形成分子内激基缔合物(excimer),又能形成分子内激基复合物(exciplex),与溶剂极性有关。在极性较大的溶剂如乙腈和甲醇中,由于激基复合物几乎完全解离因而不发射荧光,这时观察到的荧光峰蓝移而且强度增加,可以认为,这是激基缔合物存在的证明。这三个化合物的分子内激基缔合物形成的难易程度按Ⅱ>Ⅰ>Ⅲ的次序依次递降。     

外围萘修饰PAMAM树枝形聚合物的合成及其质子化过程研究

合成了外围修饰有萘基团的0～3代聚酰胺-胺树枝形聚合物GnN (n＝0～3), 化合物通过了IR, 1H NMR, 13C NMR和MALDI TOF的表征. 稳态光物理研究表明, 甲醇溶液中GnN外围萘基团与骨架胺之间发生电子转移过程, 形成最大发射峰在450 nm的激基复合物, 萘的荧光被明显猝灭; 当GnN骨架被质子化, 分子内光致电子转移过程和萘与骨架胺基间激基复合物的形成被抑制, 萘单体荧光发射大大增强; 由于质子化后树枝形聚合物骨架趋于伸展构象, 外围萘基团间相互作用增强, 部分形成最大发射峰在400 nm的激基缔合物.     

新型三嗪桥连的双1,8-萘酰亚胺衍生物的合成及其光物理行为

以1,8-萘酰亚胺和三聚氯氰为主要原料, 合成了两种由三嗪环桥连的双1,8-萘酰亚胺化合物3 和5. 采用紫外-可见光谱和荧光光谱等手段考察了两种化合物在不同溶剂中的光物理行为. 与参比化合物N-丁基-1,8-萘酰亚胺相比, 在二氯甲烷、三氯甲烷和甲醇等极性溶剂中, 化合物3和5除了在短波区(λ<400 nm)存在1,8-萘酰亚胺的特征荧光发射峰外, 在长波区(>450 nm)均产生一个较强的新荧光发射峰, 表现出分子内激基缔合物的光物理行为. 与化合物5相比, 由于化合物3特殊的构象异构, 其荧光强度发生严重的猝灭. 在非极性溶剂甲基环己烷中, 化合物5 由于存在较强的分子间氢键作用而聚集, 受激后形成了较稳定的分子间激基缔合物, 但未观察到明显的分子内激基缔合物的形成. 在甲苯溶剂中, 化合物3和5与甲苯分子形成了激基复合物, 并未形成分子内激基缔合物. 进一步研究3和5的固态激发态性质, 发现化合物3和5的固体薄膜受激后分别在465和469 nm处出现激基缔合物的特征荧光发射峰.     

Exciplex and excimer molecular probes: detection of conformational flip in a myo-inositol chair

2-O-tert-Butyldimethylsilyl-4,6-bis-O-pyrenoyl-myo-inositol-1,3,5-orthoformate (6) and 2-O-tert-butyldimethylsilyl-4-O-[4-(dimethylamino)benzoyl]-6-O-pyrenoyl-myo-inositol-1,3,5-orthoacetate (10) adopt conformationally restricted unstable chairs with five axial substituents. In the symmetrical diester 6, the two pi-stacked pyrenoyl groups are electron acceptor-donor partners, giving a strong intramolecular excimer emission. In the mixed ester 10, the pyrenoyl group is the electron acceptor and the 4-(dimethylamino)benzoyl ester is the electron donor, giving a strong intramolecular exciplex emission. The conformation of the mixed ester 10 was assessed using 1H NMR spectroscopy (1H-NOESY) and computational studies. which showed the minimum inter-centroid distance between the two aromatic systems to be approximately 3.9 A. Upon addition of acid, the orthoformate/orthoacetate trigger in 6 and 10 was cleaved, which caused a switch of the conformation of the myo-inositol ring to the more stable penta-equatorial chair, leading to separation of the aromatic ester groups and loss of excimer and exciplex fluorescence, respectively. This study provides proof of principle for the development of novel fluorescent molecular probes.     

Excitation conversion in excimers and exciplexes of aromatic hydrocarbons

Flurorescence spectra of a number of aromatic hydrocarbons, their excimers and exciplexes with diethylaniline have been measured in n-hexane under aerobic conditions. It has been found that the value of the red shift of the structureless excimer or exciplex band in reference to the monomer fluorescence band is about 4200 or 3000 cm⁻¹, respectively. For indole—ethanol exciplexes the red shift was about 3700 cm⁻¹. It is suggested, that the shift depends on the intramolecular vibrations in the quencher accepting the vibrational energy from the electronically excited donor molecule. It has been proposed that excimer and exciplex fluorescence occurs due to the donor emission of a number of quanta from the virtual levels.     

Photophysical processes of a copolymer containing 1,1'-binaphthyl-2,2'-diamino and carbazolyl units

The photophysical processes of copolymer formed by copolymerization of 2,2'-dimethacrylamido-1,1'-binaphthyl (DMBN) with vinylcarbazole (VCZ) have been carefully studied. The results show that when the solution of copolymer (DMBN-VCZ) in THF located in low concentration range (< 10(-3) mg/ml), the fluorescence emission is in good agreement with that of DMBN monomer and the excimer is formed with gradual increase in concentration of copolymer (DMBN-VCZ). The fluorescence of copolymer (DMBN-VCZ) can be quenched both by electron donors and acceptors where the quenching effects follow the Stern-Volmer equation. The dimolecular exciplex between copolymer (DMBN-VCZ) and N,N-dimethylaniline (DMA) are formed and the triple exciplexes are also observed in the same system.     

Short-chain model studies on emission properties of poly(9-vinylphenanthrene-co-p-N,N-dimethylaminostyrene): Exciplex quenching and subsequent formation of another fluorescent exciplex

The emission properties of 1-(4-dimethylaminophenyl)-3-(9-phenanthryl)propane, Ph(CH₂)₃ DMA, and 1,3-di-(9-phenanthyrl)propane, Ph(CH₂)₃Ph, were studied in comparison with those of poly(9-vinylphenanthrene-co-p-N,N-dimethylaminostyrene). Ph(CH₂)₃DMA showed an intense intramolecular exciplex fluorescence in dioxane. Ph(CH₂)₃Ph did not exhibit a clear intramolecular excimer fluorescence. The quenching of the intramolecular exciplex by several electron acceptors was studied. As a result moderate electron acceptors, such as cyanobenzene, methyl benzoate, and acrylonitrile, selectively quenched the intramolecular exciplex, and in the case of cyanobenzene the subsequent formation of another fluorescent exciplex was observed. The results were discussed in terms of the reduction potentials of electron accepting quenchers.     

Determination of the barrier to intramolecular exciplex formation in a jet-cooled, bichromophoric molecule

The emissive properties of a bichromophor molecule (1) are reported. This contains an anilino group as an electron donor (D) and a 1-cyanonaphthalene group as an electron acceptor (A) interconnected by a saturated hydrocarbon bridge of limited flexibility, which holds D and A far apart in the electronic ground state. The emission spectrum of 1, both in solution and in the gas phase, indicates that quantitative formation of an intramolecular exciplex between D and A occurs. This exciplex formation was studied as a function of excitation energy in molecules of 1 isolated in a supersonic free jet. A barrier of 1700 ± 200 cm⁻¹ was found between the Franck-Condon excited conformation and the conformation of the exciplex. Although this value is significantly higher than that reported earlier for exciplex formation between chromophores connected by a simple polymethylene chain (≈ 900 cm⁻¹) it is much lower than the barrier predicted for folding the bridge in 1 sufficiently to bring D and A in close contact. A tentative explanation of this discrepancy is given.     

A novel fluorescence probe for micellization of amphiphilic molecules in water based on intramolecular exciplex formation

A novel friction‐sensitive fluoresence probe based on intramolecular exciplex formation, (9‐anthrylmethyloxymethyl)pyrene (AMOP), was used to study the micellization of amphiphilic molecules such as sodium dodecyl sulfate (SDS) and hydrocarbon‐modified polyethylene glycol (HM‐PEG) in water. Results demonstrate that AMOP can serve as a sensitive probe for micellization of both SDS and HM‐PEG. In addition, AMOP reveals information about the microviscosity of SDS and HM‐PEG micelles, which is in good agreement with the results obtained from other fluorescence probes based on intramolecular excimer such as dipyrenylpropane (Py(CH₂)₃Py) and bis(1‐pyrenylmethyl) ether (dipyme, PyCH₂OCH₂Py).     

Review: fluorescent cyclodextrins for molecule sensing

Cyclodextrins (CDs), which are spectroscopically inert, were converted into fluorescent CDs by modification with one or two fluorophores. Many fluorescent CDs changed the fluorescent intensities upon addition of guest compounds, causing the locational change of the fluorophore mostly from inside to outside of the CD cavities. On this basis, the fluorescent CDs were used as fluorescent chemosensors for molecule recognition. Modified CDs bearing two naphthalene or pyrene moieties exhibit intramolecular excimer emission and their guest-responsive excimer intensity variations were used for molecule sensing. Fluorescent CDs bearing a dansyl moiety decreased the fluorescence intensity upon guest addition, reflecting the environmental change around the fluorophore from the hydrophobic interior of the CD cavities to bulk water solution. Modified CDs bearing a p-N,N-dimethylaminobenzoyl (DMAB) moiety exhibit dual emissions from nonpolar planar (NP) and twisted intramolecular charge transfer (TICT) excited states, and the TICT emission intensity was useful for sensing molecules. A biotin-bound DMAB system was also constructed, and the presence of the protein (avidin) was found to enhance the NP fluorescence. This avidin-bound DMAB system showed higher sensitivities and stronger binding ability for guest species than the system without avidin.     

Tuning emissive states in electrogenerated chemiluminescence

Electrogenerated chemiluminescence (ECL) arising from the reaction of radical ions has previously be shown to arise from a variety of states including excited singlets, triplets, excimers, and exciplexes. In this work we describe two systems that form emissive states in ECL with different properties than those when formed with photoluminescence. The first system involves the reaction of the anthracene radical anion with the radical cation of 4,N,N-trimethylaniline. ECL from this system exhibited an exciplex whose energy and intensity relative to the emission from the anthracene singlet could be tuned by adjusting the solvent permittivity and ionic strength. Under conditions considered extreme for electrochemical experiments, no added electrolyte in dimethoxyethane, the relative intensity of the anthracene-related exciplex, formed from the encounter complex, was 8 times greater and red-shifted from that generated by photoluminescence in the same solution with 100-fold exciplex partner added. In the second system examined, the benzophenone radical anion reacted with the radical cation of either phenoxathiin or 4-methoxythioanisole; the ECL emission was from the benzophenone triplet state and an excimer. The excimer, a species not seen with photoluminescence, predominated as the benzophenone concentration was elevated into the low millimolar range. The results from these two simple systems clearly demonstrate that the radical ion annihilation pathway of ECL can generate different emissive states than those formed following photoexcitation.     

Electronic energy trapping in a crystal due,to a dopant of higher excitation energy than the host

An excimer emitting crystal (9-cyanoanthracene) doped with a guest molecule (9-methoxyanthracene) having its first singlet level ca. 2000 cm^?1 above the host singlet exciton band exhibits efficient energy trapping as demonstrated by host sensitized, red-shifted emission and hetero-photodimerization. It is considered that the trapping is due to exciplex formation between host and guest molecules.     

Quenching of exciplex and charge-transfer complex fluorescence of poly(N-vinylcarbazole) – benzanthrone system

When benzanthrone (Bt), a weak electron acceptor, is doped into poly(N-vinylcarbazole) (PVCz) solution or film, an excited carbazole chromophore (D*) interacts with Bt to form a new exciplex state, which gives a broad fluorescence band (λ_max = 440 nm) in solution and a new state, which gives broad fluorescence (λ_max = 550 nm) in the film. In order to elucidate the origin of these new states, we have studied the results of experiments for absorption, concentration dependence of the excimer and exciplex fluorescence quenching, both in solution and in the film, and electric field-induced fluorescence quenching in the film. Taking into account that (i) the new state formation in the PVCz film containing small amounts of Bt enhances the photocurrent in the absorption region, where the photon energy is insufficient to excite polymer molecules directly into the conduction state, (ii) the 550 nm fluorescence of the PVCz - Bt system in film is only partly quenched by electric field, (iii) the appearance of structureless tail in the fluorescence excitation spectrum, the charge transfer interaction model of the PVCz - Bt system in film is proposed.