有机发光二极管中三重态激子的单重态转换

在OLED的研究中如何充分利用三重态激子以提高器件的电-光转换效率一直是人们关注的问题,近年来出现的经热激活逆向上转换过程获得延迟荧光的办法,使OLED的研究出现了一派崭新的前景。本文综合前人的工作对有关这一领域的研究基础,如：电子跃迁、激发态的分裂、单重态/三重态的交换能量、载流子的重合和激子的形成,以及在纯有机化合物与有机-过渡金属配合物中的电荷转移（CT）问题等,进行了较详细的讨论。     

有机分子三重激发态的调控与应用

对近期有机分子三重激发态调控的研究进展进行了总结评述。控制分子的三重激发态性质,可以制备多种具有新颖性质的分子,如用于可激活光动力治疗(PDT)的光敏剂、磷光分子探针与生物标识试剂,以及可控的三重态湮灭上转换等。但目前对三重态控制方面的研究相对较少,其中的规律也很不明确。近期有文献陆续报道了使用超分子方法和共价修饰法进行的三重态调控,利用的光物理过程有单重态能量转移、三重态能量转移、电子转移等等。现有研究结果表明,三重态的调控规律与单重态的调控规律有所不同,例如:发色团的单重激发态(荧光)往往可以被光诱导电子转移(PET)所猝灭,但是在多个例子中已发现,相同发色团的三重态并不能被PET所猝灭。本文总结的研究结果及所作的分析,将对该领域的分子结构设计及后续研究起到一定的促进作用。     

Macrocycle-Based Crystalline Supramolecular Assemblies Built with Intermolecular Charge-Transfer Interactions

Synthetic macrocycles have served as principal tools for supramolecular chemistry, have greatly extended the scope of organic charge transfer (CT) complexes, and have proved to be of great practical value in the solid state during the past few years. In this Minireview, we summarize the research progress on the macrocycle-based crystalline supramolecular assemblies primarily driven by intermolecular CT interactions (a.k.a. macrocycle-based crystalline CT assemblies, MCCAs for short), which are classified by their donor–acceptor (D-A) constituent elements, including simplex macrocyclic hosts, heterogeneous macrocyclic hosts, and host–guest D-A pairs. Particular attention will be focused on their diverse functions and applications, as well as the underlying CT mechanisms from the perspective of crystal engineering. Finally, the remaining challenges and prospects are outlined.     

离子液体[Bmim][BF_4]中卟啉的三线态动力学

室温离子液体由于其几乎不挥发、稳定性突出、良好的电化学性能以及结构与性能的可设计性等优点,在诸多领域得到了深入的研究和广泛的应用。与传统的普通溶剂不同,离子液体的本质特点之一是其内部的微观结构具有微不均匀性。本文通过对四苯基卟啉(TPP)分子在离子液体[Bmim][BF_4]中的三线态动力学研究,发现在激光作用下,TPP的三线态寿命由2.95μs显著增加到184μs。进一步分析表明,这一现象很可能是由于离子液体的微结构在激光诱导下发生变化,被激光场或者离子诱导极化的氧气分子在离子液体微不均匀性环境中发生重新分布而引起的。     

Intermolecular Charge-Transfer Luminescence by Self-Assembly of Pyridinium Luminophores in Solutions

Designing a luminophore for application both in solution and in the solid state is a highly challenging task given the distinct nature of intermolecular interactions in these phases. In this context, we demonstrate that self-assembly of non-emissive charged pyridinium luminophores enables luminescence in solutions through a mechanism that is characteristic for the crystal state. Specifically, protonation of pyridine luminophore subunits in a solution promotes oligomer formation through intermolecular π⁺-π interactions, leading to an intermolecular charge-transfer type luminescence. The luminescence turn-on by protonation is utilized for a highly efficient solution-state luminescent sensing of hydrogen chloride and sulfonic acids (TfOH, TsOH and MsOH) with detection limits spanning the range from 0.06 to 0.33 ppm. The protonation followed by self-assembly results in a bathochromic shift of the emission from 420 nm to 550 nm.     

Aromaticity Reversal in the Lowest Excited Triplet State of Archetypical Möbius Heteroannulenic Systems

The aromaticity reversal in the lowest triplet state (T₁) of a comparable set of Hückel/Möbius aromatic metalated expanded porphyrins was explored by optical spectroscopy and quantum calculations. In the absorption spectra, the T₁ states of the Möbius aromatic species showed broad, weak, and ill‐defined spectral features with small extinction coefficients, which is in line with typical antiaromatic expanded porphyrins. In combination with quantum calculations, these results indicate that the Möbius aromatic nature of the S₀ state is reversed to Möbius antiaromaticity in the T₁ state. This is the first experimental observation of aromaticity reversal in the T₁ state of Möbius aromatic molecules.     

Stacking Effects on Anthraquinone/DNA Charge-Transfer Electronically Excited States

The design of more efficient photosensitizers is a matter of great importance in the field of cancer treatment by means of photodynamic therapy. One of the main processes involved in the activation of apoptosis in cancer cells is the oxidative stress on DNA once a photosensitizer is excited by light. As a consequence, it is very relevant to investigate in detail the binding modes of the chromophore with DNA, and the nature of the electronically excited states that participate in the induction of DNA damage, for example, charge-transfer states. In this work, we investigate the electronic structure of the anthraquinone photosensitizer intercalated into a double-stranded poly(dG-dC) decamer model of DNA. First, the different geometric configurations are analyzed by means of classical molecular dynamics simulations. Then, the excited states for the most relevant poses of anthraquinone inside the binding pocket are computed by an electrostatic-embedding quantum mechanics/molecular mechanics approach, where anthraquinone and one of the nearby guanine residues are described quantum mechanically to take into account intermolecular charge-transfer states. The excited states are characterized as monomer, exciton, excimer, and charge-transfer states based on the analysis of the transition density matrix, and each of these contributions to the total density of states and absorption spectrum is discussed in terms of the stacking interactions. These results are relevant as they represent the footing for future studies on the reactivity of anthraquinone derivatives with DNA and give insights on possible geometrical configurations that potentially favor the oxidative stress of DNA.     

Photosensitized Thymine Dimerization via Delocalized Triplet Excited States

A new mechanism of photosensitized formation of thymine (Thy) dimers is proposed, which involves generation of a delocalized triplet excited state as the key step. This is supported by chemical evidence obtained by combining one benzophenone and two Thy units with different degrees of freedom, whereby the photoreactivity is switched from a clean Paternò–Büchi reaction to a fully chemo‐, regio‐, and stereoselective [2+2] cycloaddition.     

吩噻嗪衍生物的分子内电荷转移激发态的特性

A series of N-bonded donor-acceptor derivatives of phenothiazine containing benzene (PHPZ), anisole (ANPZ), pyridine (PYPZ), naphthalene (NAPZ), acetophenone (PEPZ), and benzonitrile (BNPZ) as an electron acceptor was synthesized. Their photophysical properties were investigated in solvents of different polarities by absorption and emission techniques. These studies clearly reveals the existence of an intramolecular charge transfer (ICT) excited state in the latter four compounds. The solvent dependent Stokes shift values were analyzed by the modified Lippert-Mataga equation to obtain the excited state dipole moment values. The large excited state dipole moment suggests that the full electron transfer takes place in the A-D systems. The obtained values of redox potentials indicate that both subunits of all the A-D molecules studied interact very weakly in the ground states. The results obtained from the analysis of the CT fluorescence spectra confirm that the small conformational changes accompanying excited state charge transfer, the twist angle between the donor and acceptor moieties in the excited 1CT state seems to be similar to that in the ground state.     

Tuning the Triplet Excited State of Bis(dipyrrin) Zinc(II) Complexes: Symmetry Breaking Charge Transfer Architecture with Exceptionally Long Lived Triplet State for Upconversion

Zinc(II) bis(dipyrrin) complexes, which feature intense visible absorption and efficient symmetry breaking charge transfer (SBCT) are outstanding candidates for photovoltaics but their short lived triplet states limit applications in several areas. Herein we demonstrate that triplet excited state dynamics of bis(dipyrrin) complexes can be efficiently tuned by attaching electron donating aryl moieties at the 5,5′-position of the complexes. For the first time, a long lived triplet excited state (τ_T=296 μs) along with efficient ISC ability (Φ_Δ=71 %) was observed for zinc(II) bis(dipyrrin) complexes, formed via SBCT. The results revealed that molecular geometry and energy gap between the charge transfer (CT) state and triplet energy levels strongly control the triplet excited state properties of the complexes. An efficient triplet–triplet annihilation upconversion system was devised for the first time using a SBCT architecture as triplet photosensitizer, reaching a high upconversion quantum yield of 6.2 %. Our findings provide a blueprint for the development of triplet photosensitizers based on earth abundant metal complexes with long lived triplet state for revolutionary photochemical applications.     

The Reaction of Triplet State Benzophenone with Acetylacetone

Irradiation of benzophenone in acetic acid containing acetylacetone resulted in regiospecific addition to form cis-2,2-dihpenyl-3-hydroxy-3-methyl-4-acetyloxetane and the rearrangement products therefrom. In the co-presence of copper ions, the regiospecificity is scrambled to give these products and a small amount of 1,1-diphenyl-1-buten-3-one, the secondary decomposition product of the other oxetane arising from the alternative orientation of the addition.     

Intramolecular Excited State Electronic Coupling Along an alpha-Helical Peptide

Several families of peptides composed of alternating L-alanine (Ala) and alpha-aminoisobutyric acid (Aib) residues with an appended N,N-dimethylanilino and/or 2-naphthalenyl group exist in MeOH and CDCl(3) as alpha-helices. Steady state and time-resolved fluorescence measurements show that the distance and dihedral angle between the appended donor and acceptor and the alignment of the vectors for intramolecular charge transfer interaction (from donor to acceptor) with or against that of the helical dipole moment significantly influence the efficiency of photoinduced electronic coupling and, hence, of intramolecular fluorescence quenching.     

Coherent Vibration and Femtosecond Dynamics of the Platinum Complex Oligomers upon Intermolecular Bond Formation in the Excited State

Femtosecond time-resolved absorption and picosecond time-resolved emission measurements were carried out for highly concentrated aqueous solutions of K₂[Pt(CN)₄] to investigate excited-state dynamics of the [Pt(CN)₄²⁻] oligomers formed with metallophilic interactions. Time-resolved absorption spectra exhibit complicated dynamics that are represented with five time constants. Among them, the 90-ps and 400-ps dynamics were assigned to the S₁ → T₁ intersystem crossing of the trimer and tetramer coexisting in the solution by comparison with the fluorescence decays. Clear oscillations of transient absorption were observed in the first few picoseconds, and the frequency-detected-wavelength 2D analysis revealed that the 135-cm⁻¹ and 65-cm⁻¹ oscillations arise from the Pt–Pt stretch motions of the S₁ trimer and S₁ tetramer, respectively. The obtained time-resolved spectroscopic data provide a clear view of the excited-state dynamics of the [Pt(CN)₄²⁻] oligomers in the femto-/picosecond time region.