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。     

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.     

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.     

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.     

Tuning Ground States of Bis(triarylamine) Dications: From a Closed‐Shell Singlet to a Diradicaloid with an Excited Triplet State

Three bis(triarylamine) dications were isolated by using weakly coordinating anions. Their electronic structures in the ground state were investigated by various experiments in conjunction with theoretical calculations. The ground‐state electronic structures of these species were tunable by substituent effects, with two of them as closed‐shell singlets and one of them as an open‐shell singlet in the solid state. The excited state of the latter is thermally accessible, indicated by EPR and SQUID measurements. The work provides a new and stable diradicaloid structure motif with an excited triplet sate.     

On the Apparent Lack of Oxygen Quenching of Triplet Excited States

The early observation that excited triplet states obtained chemically from trimethyldioxetane (and subsequent energy transfers) appeared not to be quenched by oxygen is now shown to be an artifact; acetaldehyde is a product of the reaction and via chemical reactions it scavenges oxygen present in the medium; the attendant extended lifetime of the triplet states then permits their employment in photochemical-type reactions. The effect of the aldehyde can be over-ridden through an efficient introduction of an excess of oxygen into the liquid reaction phase.