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.     

酸酐—吩噻嗪电荷转移络合物的热力学测定

测定了７种酸酐与吩噻嗪在２８８１５、２９８１５、３０８１５和３１８１５Ｋ时形成电荷转移络合物的平衡常数Ｋ值，并计算出了它们对应的△Ｈ、△Ｓ值和酸酐的电子亲核能（ＥＡ）值，以此表征了这类电荷转移络合物，结果表明△Ｈ－ＥＡ和Ｋ－ＥＡ呈线性关系。     

两种吩噻嗪衍生物的合成，光学性质及其电化学性质

The synthesis, luminescence and electrochemical properties of two novel phenothiazine derivatives were presented, which exhibit good one-photon fluorescence emission. The quantum yields and solvent effects of them were studied in detail. Compound 3,7-bis（2-4＇-imidazolylbenzylidenehydrazonoethyl）-（0-ethylphenothiazine） （5） was used as an effective initiator, of which two-photon fluorescence spectra were investigated under 800 nm fs laser pulse and the measured two-photon absorption cross-section was 18 × 10^-50 cm^4·s per photon. Two-photon initiated polymerization microfabrication experiments were carried out. X-ray diffraction analyses revealed that the shape of the compound 3,7-bis（2-pyrid-4＇-ylmethylidenehydrazonoethyl）-（0-ethylphenothiazine） （4） looks like a butterfly with nearly planar wings. The dihedral angle of the two benzene rings is 37.6° and there is an obvious π-π stacking interaction between the molecules in the crystal.     

吩噻嗪、N-甲基吩噻嗪及其自由基正离子的结构和电子光谱的理论研究

用INDO系列方法对吩噻嗪、N-甲基吩噻嗪及其自由基正离子进行了几何构型优化,中性分子为蝶状折叠形,自由基正离子为平面构型.以优化构型为基础,计算了上述四种分子、离子的电荷密度、自旋密度、键序和电子光谱,对光谱进行理论指认的同时,讨论了从中性分子到离子谱带红移的原因.所有理论计算值均与实验值一致.     

不饱和酸酐—吩噻嗪电荷转移络合物结构的探讨

用ＩＲ和ＵＶ两种方法首次研究了吩噻嗪与７个酸酐形成的电荷转移络合物，测定了它们的组成和溶剂效应，并推测出酸酐与吩噻嗪形成电荷转移络合物时相互作用的方式（结构）。     

N—乙基吩噻嗪及其自由基正离子的结构和电子光谱的理论研究

用ＩＮＤＯ系列方法对Ｎ－乙基吩噻嗪及其自由基正离子进行了几何构型优化，得到中性分子为蝶状折叠形，自由基正离子为平面构型，以优化构型为基础计算其电荷密度，自旋密度键序和电子光谱。对光谱进行理论指认并讨论了从中性分子到离子谱带红移的原因，理论计算结果法与实验结果一致。     

吩噻嗪、N-甲基吩噻嗪及其自由基正离子的结构和电子光谱的理论研究

用INDO系列方法对吩噻嗪、N-甲基吩噻嗪及其自由基正离子进行了几何构型优化, 中性分子为蝶状折叠形, 自由基正离子为平面构型。以优化构型为基础,计算了上述四种分子、离子的电荷密度、自旋密度、键序和电子光谱, 对光谱进行理论指认的同时, 讨论了从中性分子到离子谱带红移的原因。所有理论计算值均与实验值一致。     

含吩噻嗪氧化物的N-丙烯酰基吩噻嗪氧化物的合成及其荧光行为

含吩噻嗪氧化物的Ｎ 丙烯酰基吩噻嗪氧化物的合成及其荧光行为刘向前杜福胜李子臣李福绵（北京大学化学与分子工程学院北京１００８７１）关键词Ｎ 丙烯酰基吩噻嗪氧化物，荧光光谱，荧光结构自猝灭我们曾报道过含给电子性生色基团的丙烯酰类单体及其聚合物的荧光行为...     

Synthesis of 2-Azastilbene Derivatives with Intramolecular Charge Transfer

The condensation reaction of 2-cyanomethyl-5-nitropyridine with aromatic aldehydes has been carried out with the aim of preparing 2-azastilbene derivatives having intramolecular charge transfer. The yield of the condensation products can be increased if the reaction is carried out in the medium used for obtaining the starting 2-cyanomethyl-5-nitropyridine without separating or purifying it. The electronic absorption spectra of the compounds show a charge-transfer band, the energy of which increases and the intensity falls with lowering of the electron-donor properties of the substituent in the 4-position. Introduction of the heteroatom into the acceptor part when changing from the stilbene to the 2-azastilbene system is accompanied by a decrease in the energy and increase in the intensity of the charge-transfer electronic transition.     

Influence of Sulfur Atoms on TADF Properties from Through-Space Charge Transfer Excited States

The harnessing of heavy atom effect of chalcogen elements offers a way for boosting the thermally activated delayed fluorescence (TADF) of purely organic luminescent materials that can harvest triplet excitons. However, the conformational and electronic variations induced by the heavy and large atoms may also have adverse effects on the TADF properties. Herein, the design, synthesis, and structures of a new type of through-space charge transfer (TSCT) emitters containing benzothiazino[2,3,4-kl]phenothiazine (DPTZ) as the donor unit are reported. The influences of S atoms on the emission properties have been systematically investigated by means of theoretical simulations, electrochemical and spectroscopic studies. Although the presence of π-stacking interactions and calculated spin-orbit coupling (SOC) values are beneficial for TSCT-TADF properties, the triplet TSCT states are uplifted to above the locally excited (LE) state of the acceptor moieties. As a result, the new emitters display longer delayed fluorescence lifetimes (τ_DF) of 255.0–114.3 μs and lower PLQYs of 45–61 % in comparison with the O-containing congeners (τ_DF=26.9–6.8 μs; PLQYs=74–71 %). This work highlights that a full consideration of various effects is essential when making use of heavy chalcogen atoms for the design of TADF emitters.     

黄芩素激发态分子内质予转移耦合电荷转移反应的实验和理论研究

通过稳态光谱实验和量子化学计算相结合,研究了黄芩素激发态质子转移耦合电荷转移的反应. 实验和计算中S1态吸收峰的缺失表明S1态是暗态. S1暗态导致在实验中观察不到黄芩素在乙醇溶液中的荧光峰,且固体的荧光峰很弱. 黄芩素分子的前线分子轨道和电荷差异密度表明S1态是电荷转移态,然而S2态是局域激发态. 计算的黄芩素分子的势能曲线在激发态只有一个稳定点,这表明了黄芩素激发态分子内质子转移的过程是一个无能垒的过程.     

Molecular Dynamics of Excited State Intramolecular Charge Transfer in Solution by Coherent Nuclear Wave Packets

Revealing a proper reaction coordinate in a chemical reaction is the key step towards elucidation of the molecular reaction dynamics. In this report, we investigated the dynamics of intramolecular charge transfer (ICT) of 8-aminopyrene-1,3,6-trisulfonic acid (APTS) occurring in the excited state by time-resolved fluorescence (TF) and TF spectra. Accurate reaction rates and rate-dependent nuclear wave packets in the product state allow detailed investigation of the molecular reaction dynamics. The ICT rate is solvent dependent: (34 fs)⁻¹, (87 fs)⁻¹, and (∞)⁻¹ in water, formamide, and dimethylformamide, respectively. By recording spectra of the nuclear wave packets for different reaction rates, chemical species responsible for the emission spectra can be positively identified. The origin of the wave packets can be deduced from the amplitude change of the wave packets at different reaction rates, and the vibrational modes that are associated with the reaction coordinate could be identified. Theoretical calculations of the vibrational reorganization energies reproduce the experimental spectrum of the nuclear wave packets and corroborate the conclusions.     

Photoinduced Intramolecular Charge Transfer in Donor-acceptor Dyad and Donor-bridge-acceptor Triad

The ground and excited state properties of the 60fullerene, diphenylbenzothiadiazole-triphenylamine (PBTDP-TPA) dyad and fullerene-diphenylbenzothiadiazole-triphenylamine (fullerene-PBTDP-TPA) triad were investigated theoretically using density functional theory with B3LYP functional and 3-21G basis et and time-dependent density functional theory with B3LYP functional and STO-3G basis set as well as 2D and 3D real space analysis methods. The 2D site representation reveals the electron-hole coherence on excitation. The 3D transition density shows the orientation and strength of the transition dipole moment, and the 3D charge difference density gives the orientation and result of the intramolecular charge transfer. Also, photoinduced intermolecular charge transfer (ICT) in PBTDP-TPA-fullerene triad are identified with 2D and 3D representations, which reveals the mechanisms of ICT in donor-bridge-acceptor triad on excitation. Besides that we also found that the direct superexchange ICT from donor to acceptor (tunneling through the bridge) strongly promotes the ICT in the donor-bridge-acceptor triad.     

Solvent-Induced Symmetry-Breaking Charge Transfer in an Octupolar Triphenylamine Derivative Resolved with Transient Fluorescence Spectroscopy

The excited-state symmetry-breaking charge transfer (SBCT) dynamics in quadrupolar or octupolar molecules without clear infrared markers is usually hard to be tracked directly. In this work, on the basis of the evolution of instantaneous emission dipole moment obtained by femtosecond transient fluorescence spectroscopy, we presented a real-time characterization of the solvent-induced SBCT dynamics in an octupolar triphenylamine derivative. While the emission dipole moment of the octupolar trimer in weakly polar toluene changes little during the excited-state relaxation, it exhibits a fast reduction in a few picoseconds in strongly polar tetrahydrofuran. In comparison with the uorescence dynamics of dipolar monomer, we deduced that the emitting state of the octupolar trimer in strongly polar solvent, which undergoes solvent-induced structural uctuation, changes from exciton-coupled octupolar to excitation localized dipolar symmetry. In weakly polar solvent, the octupolar symmetry of the trimer is largely preserved during the solvation stabilization.     

Synthesis and Cyclization-Induced Charge Transfer of Rectangular Bisterthiophenesiloxanes

Cyclization-modified terthiophene displays the change of emission behavior from locally excited (LE) to the intramolecular charge transfer (ICT) state. The rectangular bisterthiophenesiloxanes (DSiTh) was successfully prepared by π–π-stacking-aided hydrogen-bonding interactions. Cyclization-induced ICT in DSiTh could be observed, which was confirmed by absorption spectra, fluorescence spectra, and quantum chemistry analysis. The cyclization produces a strong intramolecular electron redistribution of a highly packed π-conjugated terthiophene. Thus, a distinctive variation of the dipole moment and a through-space ICT happen.     

Indolizino[5,6‐b]quinoxaline Derivatives: Intramolecular Charge Transfer Characters and NIR Fluorescence

Indolizino[5,6‐b]quinoxaline derivatives ( 1 a and 1 b ) with a push–pull structure were prepared to show intramolecular charge‐transfer properties. Compounds 1 a and 1 b are strongly fluorescent in aprotic solvents while symmetrical derivatives ( 2 a and 2 b ) were non‐fluorescent. The π‐expanded α–α linked dimer ( 10 ) of indolizino[5,6‐b]quinoxaline 1 b was serendipitously obtained to show NIR absorption over 800 nm and the fluorescence edge reached to 1400 nm.     

Fluorescent Probes Based on Charge and Proton Transfer for Probing Biomolecular Environment

Fluorescent probes for sensing fundamental properties of biomolecular environment, such as polarity and hydration, help to study assembly of lipids into biomembranes, sensing interactions of biomolecules and imaging physiological state of the cells. Here, we summarize major efforts in the development of probes based on two photophysical mechanisms: (i) an excited-state intramolecular charge transfer (ICT), which is represented by fluorescent solvatochromic dyes that shift their emission band maximum as a function of environment polarity and hydration; (ii) excited-state intramolecular proton transfer (ESIPT), with particular focus on 5-membered cyclic systems, represented by 3-hydroxyflavones, because they exhibit dual emission sensitive to the environment. For both ICT and ESIPT dyes, the design of the probes and their biological applications are summarized. Thus, dyes bearing amphiphilic anchors target lipid membranes and report their lipid organization, while targeting ligands direct them to specific organelles for sensing their local environment. The labels, amino acid and nucleic acid analogues inserted into biomolecules enable monitoring their interactions with membranes, proteins and nucleic acids. While ICT probes are relatively simple and robust environment-sensitive probes, ESIPT probes feature high information content due their dual emission. They constitute a powerful toolbox for addressing multitude of biological questions.