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1.
Synthetic Control of Spectroscopic and Photophysical Properties of Triarylborane Derivatives Having Peripheral Electron‐Donating Groups 下载免费PDF全文
Dr. Akitaka Ito Kazuyoshi Kawanishi Dr. Eri Sakuda Prof. Dr. Noboru Kitamura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):3940-3953
The spectroscopic and photophysical properties of triarylborane derivatives were controlled by the nature of the triarylborane core (trixylyl‐ or trianthrylborane) and peripheral electron‐donating groups (N,N‐diphenylamino or 9H‐carbazolyl groups). The triarylborane derivatives with and without the electron‐donating groups showed intramolecular charge‐transfer absorption/fluorescence transitions between the π orbital of the aryl group (π(aryl)) and the vacant p orbital on the boron atom (p(B), π(aryl)–p(B) CT), and the fluorescence color was tunable from blue to red by the combination of peripheral electron‐donating groups and a triarylborane core. Detailed electrochemical, spectroscopic, and photophysical studies of the derivatives, including solvent dependences of the spectroscopic and photophysical properties, demonstrated that the HOMO and LUMO of each derivative were determined primarily by the nature of the peripheral electron‐donating group and the triarylborane core, respectively. The effects of solvent polarity on the fluorescence quantum yield and lifetime of the derivatives were also tunable by the choice of the triarylborane core. 相似文献
2.
In Hwan Jung Jinyoung Yu Eunjae Jeong Jinseck Kim Sooncheol Kwon Hoyoul Kong Kwanghee Lee Prof. Han Young Woo Prof. Hong‐Ku Shim Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(12):3743-3752
We have synthesized four types of cyclopentadithiophene (CDT)‐based low‐bandgap copolymers, poly[{4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl}‐alt‐(2,2′‐bithiazole‐5,5′‐diyl)] ( PehCDT‐BT ), poly[(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl)‐alt‐(2,2′‐bithiazole‐5,5′‐diyl)] ( PocCDT‐BT ), poly[{4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl}‐alt‐{2,5‐di(thiophen‐2‐yl)thiazolo[5,4‐d]thiazole‐5,5′‐diyl}] ( PehCDT‐TZ ), and poly[(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl)‐alt‐{2,5‐di(thiophen‐2‐yl)thiazolo[5,4‐d]thiazole‐5,5′‐diyl}] ( PocCDT‐TZ ), for use in photovoltaic applications. The intramolecular charge‐transfer interaction between the electron‐sufficient CDT unit and electron‐deficient bithiazole (BT) or thiazolothiazole (TZ) units in the polymeric backbone induced a low bandgap and broad absorption that covered 300 nm to 700–800 nm. The optical bandgap was measured to be around 1.9 eV for PehCDT‐BT and PocCDT‐BT , and around 1.8 eV for PehCDT‐TZ and PocCDT‐TZ . Gel permeation chromatography showed that number‐average molecular weights ranged from 8000 to 14 000 g mol?1. Field‐effect mobility measurements showed hole mobility of 10?6–10?4 cm2 V?1 s?1 for the copolymers. The film morphology of the bulk heterojunction mixtures with [6,6]phenyl‐C61‐butyric acid methyl ester (PCBM) was also examined by atomic force microscopy before and after heat treatment. When the polymers were blended with PCBM, PehCDT‐TZ exhibited the best performance with an open circuit voltage of 0.69 V, short‐circuit current of 7.14 mA cm?2, and power conversion efficiency of 2.23 % under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW cm?2). 相似文献
3.
Adjusting the Proportion of Electron‐Withdrawing Groups in a Graft Functional Polymer for Multilevel Memory Performance 下载免费PDF全文
Linxin Wu Peng Wang Chunyu Zhang Dr. Jinghui He Dr. Dongyun Chen Jiang Jun Prof. Qingfeng Xu Prof. Jianmei Lu 《化学:亚洲杂志》2016,11(1):102-111
A polymer containing aldehyde active groups (PVB) was synthesized by atom transfer radical polymerization (ATRP), acting as a polymer precursor to graft a functional moiety via nucleophilic addition reaction. DHI (2‐(1,5‐dimethyl‐hexyl)‐6‐hydrazino‐benzo[de]isoquinoline‐1,3‐dione) and NPH (nitrophenyl hydrazine) groups, which contain naphthalimides that act as narrow traps and nitro groups that act as deep traps, were anchored onto the PVB at different ratios. A series of graft polymers were obtained and named PVB‐DHI, PVB‐DHI4‐NPH, PVB‐DHI‐NPH4, and PVB‐NPH. The chemical composition of the polymers was analyzed by 1H‐NMR spectroscopy and X‐ray photoelectron spectroscopy (XPS). Memory devices were prepared from the polymers, and I–V characteristics were measured to determine the performance. By adjusting the ratio of different electron acceptors (DHI and NPH) to 4:1, ternary memory behavior was achieved. The relationship between memory behavior of PVB‐DHIxNPHy and acceptor groups as well as their conduction mechanism were studied in detail. 相似文献
4.
meso‐Free BIII 5,10‐bis(p‐dimethylaminophenyl)subporphyrins were synthesized. They display red‐shifted absorption and fluorescence spectra, bathochromic behaviors in polar solvents, a high fluorescence quantum yield (ΦF=0.57), and a small HOMO–LUMO gap mainly due to destabilized HOMO as compared with meso‐free BIII 5,10‐diphenylsubporphyrin. This subporphyrin serves as a nice precursor of various meso‐substituted BIII subporphyrins such as BIII meso‐nitrosubporphyrin, BIII meso‐aminosubporphyrin, and meso‐meso’ linked BIII azosubporphyrin dimer. Reactions of meso‐free BIII subporphyrins with NBS or bis(2,4,6‐trimethylpyridine)bromonium hexafluorophosphate gave meso‐meso′ linked subporphyrin dimers, often as a major product along with meso‐bromosubporphyrins. 相似文献
5.
Sha Zhou Tao Yan Sha Zhou Xuewen Hua Baolei Wang Yucheng Gu Lixia Xiong Yongqiang Li Zhengming Li 《中国化学》2014,32(7):567-572
Due to a novel mode action, low toxicity to mammals and low residue characteristics, phthalic acid diamides have aroused considerable interests in agricultural chemistry. With introduction of N‐cyano, N‐trifluoroacetyl, N‐carbamoylsulfiliminyl and sulfoximinyl substituents into phthalamides, 12 novel derivatives containing trifluoromethyl moiety were designed and synthesized. All title compounds were characterized by 1H NMR and high‐resolution mass spectrometry. The preliminary results of biological activity assessment indicated that some title compounds exhibited moderate to good insecticidal activities against oriental armyworm (Pseudaletia separata Walker). In particular, Va gave higher activity against oriental armyworm and diamondback moth. The present work reported that the new trifluoromethylated diamides incorporating N‐trifluoroacetylsulfoximinyl moieties are potential lead compounds for further structure optimization, providing some insight into the relating structure‐activity relationship. 相似文献
6.
Dr. Yusuke Kinoshita Dr. Yuichi Kitagawa Prof. Dr. Hitoshi Tamiaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):9996-10001
The enhancement of the light absorption ability of synthetic chlorophyll derivatives is demonstrated. Chlorophyll derivatives directly conjugated with a difluoroboron 1,3‐diketonate group at the C3 position were synthesized from methyl pyropheophorbide‐d through Barbier acylmethylation of the C3‐formyl moiety, oxidation of the C3‐carbinol, and difluoroboron complexation of the diketonate. Electronic absorption spectra in a diluted solution showed that the synthetic conjugates gave an absorption band at λ=400–500 nm, with a Qy band shifted to a longer wavelength of λ≈700 nm. DFT calculations demonstrated that the absorption bands and redshifts were ascribable to the coupling of the LUMO of chlorin with that of the difluoroboron diketonate moiety. The introduction of a pyrenyl group at the C33‐position of the conjugate afforded an additional charge‐transfer band over λ=500 nm, producing a pigment that bridged the green gap in standard chlorophylls. 相似文献
7.
Rhodium‐Catalyzed Stereoselective Amination of Thioethers with N‐Mesyloxycarbamates: DMAP and Bis(DMAP)CH2Cl2 as Key Additives 下载免费PDF全文
Prof. Dr. Hélène Lebel Henri Piras Johan Bartholoméüs 《Angewandte Chemie (International ed. in English)》2014,53(28):7300-7304
A stereoselective Rh‐catalyzed intermolecular amination of thioethers using a readily available chiral N‐mesyloxycarbamate to produce sulfilimines in excellent yields and diastereomeric ratio is described. A catalytic mixture of 4‐dimethylaminopyridine (DMAP) and bis(DMAP)CH2Cl2 proved pivotal in achieving high selectivity. The X‐ray crystal structure of the (DMAP)2?[Rh2{(S)‐nttl}4] complex was obtained and mechanistic studies suggested a RhII‐RhIII complex as the catalytically active species. 相似文献
8.
Giseop Kwak Hong‐Qing Wang Kyu‐Han Choi Kyu‐Ho Song Soon‐Hak Kim Hyeok‐Soo Kim Sam‐Jong Lee Ho‐Young Cho Eon‐Ju Yu Hyo‐Jeong Lee Eun‐Jung Park Lee‐Soon Park 《Macromolecular rapid communications》2007,28(12):1317-1324
New poly(diphenylacetylene)s with alkoxy and fluoroalkyl groups as electron‐donating and electron‐withdrawing groups, respectively, were synthesized by using a WCl6‐n‐Ph4Sn catalyst. The polymer solutions emitted strong, bluish‐green lights when photo‐excited. The polymers that contained the electron‐donating alkoxy groups showed longer fluorescence‐maximum peaks when compared to the polymers that contained the electron‐withdrawing fluoroalkyl groups. However, such an effect of the substituent on the absorption property was not clearly seen. The emission bands of the solid films did not show any significant red shift, relative to that of the dilute solution.
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10.
Chipeng Xie Xiuli Hu Zhaoyong Guan Xiaodong Li Fuhua Zhao Yuwei Song Yuan Li Xiaofang Li Ning Wang Changshui Huang 《Angewandte Chemie (International ed. in English)》2020,59(32):13542-13546
The properties of graphdiyne (GDY), such as energy gap, morphology, and affinity to alkali metals, can be adjusted by including electron‐withdrawing/donating groups. The push–pull electron ability and size differences of groups play a key role on the partial property adjusting of GDY derivatives MeGDY, HGDY, and CNGDY. Cyano groups (electron‐withdrawing) and methyl groups (electron‐donating) decrease the band gap and increase the conductivity of the GDY network. The cyano and methyl groups affects the aggregation of GDY, providing a higher number of micropores and specific surface area. These groups also endow the original GDY additional advantages: the stronger electronegativity of cyano groups increase the affinity of GDY frameworks to lithium atoms, and the larger atomic volume of methyl groups increases the interlayer distance and provides more storage space and diffusion tunnels. 相似文献
11.
Corentin Rinfray Dr. Guillaume Izzet Prof. Dr. Jean Pinson Dr. Sarra Gam Derouich Dr. Jean‐Jacques Ganem Dr. Catherine Combellas Dr. Frédéric Kanoufi Prof. Dr. Anna Proust 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(41):13838-13846
Polyoxometalates (POMs) are attractive candidates for the rational design of multi‐level charge‐storage materials because they display reversible multi‐step reduction processes in a narrow range of potentials. The functionalization of POMs allows for their integration in hybrid complementary metal oxide semiconductor (CMOS)/molecular devices, provided that fine control of their immobilisation on various substrates can be achieved. Owing to the wide applicability of the diazonium route to surface modification, a functionalized Keggin‐type POM [PW11O39{Ge(p‐C6H4‐C?C‐C6H4‐${{\rm N}{{+\hfill \atop 2\hfill}}}$ )}]3? bearing a pending diazonium group was prepared and subsequently covalently anchored onto a glassy carbon electrode. Electron transfer with the immobilised POM was thoroughly investigated and compared to that of the free POM in solution. 相似文献
12.
trans/cis‐Isomerization of Fluorene‐Bridged Azo Chromophore with Significant Two‐Photon Absorbability at Near‐Infrared Wavelength 下载免费PDF全文
Prof. Dr. Chih‐Chien Chu Ya‐Chi Chang Bo‐Kai Tsai Prof. Dr. Tzu‐Chau Lin Prof. Dr. Ja‐Hon Lin Prof. Dr. Vincent K. S. Hsiao 《化学:亚洲杂志》2014,9(12):3390-3396
Azo‐containing materials have been proven to possess second‐order nonlinear optical (NLO) properties, but their third‐order NLO properties, which involves two‐photon absorption (2PA), has rarely been reported. In this study, we demonstrate a significant 2PA behavior of the novel azo chromophore incorporated with bilateral diphenylaminofluorenes (DPAFs) as a π framework. The electron‐donating DPAF moieties cause a redshifted π–π* absorption band centered at 470 nm, thus allowing efficient blue‐light‐induced trans‐to‐cis photoisomerization with a rate constant of 2.04×10?1 min?1 at the photostationary state (PSS). The open‐aperture Z‐scan technique that adopted a femtosecond (fs) pulse laser as excitation source shows an appreciably higher 2PA cross‐section for the fluorene‐derived azo chromophore than that for common azobenzene dyes at near‐infrared wavelength (λex=800 nm). Furthermore, the fs 2PA response is quite uniform regardless of the molecular geometry. On the basis of the computational modeling, the intramolecular charge‐transfer (ICT) process from peripheral diphenylamines to the central azo group through a fluorene π bridge is crucial to this remarkable 2PA behavior. 相似文献
13.
Roberto Martín Liliana B. Jiménez Dr. Mercedes Álvaro Dr. J. C. Scaiano Prof. Dr. Hermenegildo García Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(35):8751-8759
2‐Azaxanthone, a nitrogenated derivative of the well‐studied organic chromophore xanthone, has been covalently bound through 2‐(ethylthio)ethylamido linkers to the carboxylic acid groups of short, soluble single‐walled carbon nanotubes (CNTs) of 450 nm average length, and the resulting azaxanthylium‐functionalized CNTs (AZX‐CNT, 8.5 wt % AZX content) characterized by solution 1H NMR, Raman and IR spectroscopy and thermogravimetric analysis. Comparison of the quenching of the triplet excited state of AZX (steady‐state and time‐resolved) and of the transient optical spectra of CNTs and AZX‐CNT shows that the covalent linkage boosts the interaction between the azaxanthylium moiety and the short CNT units. The triplet excited state of the azaxanthylium derivative is quenched by CNT with and without covalent bonding, but when it is covalently bonded, the singular transient spectrum is compatible with the photogeneration of electron holes through electron transfer from CNT to excited azaxanthylium units. 相似文献
14.
Aline Gégout Dr. Jean‐François Nierengarten Prof. Dr. Béatrice Delavaux‐Nicot Dr. Carine Duhayon Dr. Alix Saquet Dr. Andrea Listorti Dr. Abdelhalim Belbakra Claudio Chiorboli Dr. Nicola Armaroli Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(35):8825-8833
Diethylamino‐substituted oligophenylenevinylene (OPV) building blocks have been prepared and used for the synthesis of two [60]fullerene–OPV dyads, F‐D1 and F‐D2 , which exhibit different conjugation length of the OPV fragments. The electrochemical properties of these acceptor–donor dyads have been studied by cyclic voltammetry. The first reduction is always assigned to the fullerene moiety and the first oxidation centered on the diethylaniline groups of the OPV rods, thus making these systems suitable candidates for photoinduced electron transfer. Both the OPV and the fullerene‐centered fluorescence bands are quenched in toluene and benzonitrile, which suggests the occurrence of photoinduced electron transfer from the amino‐substituted OPVs to the carbon sphere in the dyads in both solvents. By means of bimolecular quenching experiments, transient absorption spectral fingerprints of the radical cationic species are detected in the visible (670 nm) and near‐IR (1300–1500 nm) regions, along with the much weaker fullerene anion band at λmax=1030 nm. Definitive evidence for photoinduced electron transfer in F‐D1 and F‐D2 comes from transient absorption measurements. A charge‐separated state is formed within 100 ps and decays in less than 5 ns. 相似文献
15.
Difluorenyl carbo‐Benzenes: Synthesis,Electronic Structure,and Two‐Photon Absorption Properties of Hydrocarbon Quadrupolar Chromophores 下载免费PDF全文
Dr. Iaroslav Baglai Manuel de Anda‐Villa Rodrigo M. Barba‐Barba Corentin Poidevin Dr. Gabriel Ramos‐Ortíz Dr. Valérie Maraval Dr. Christine Lepetit Dr. Nathalie Saffon‐Merceron Dr. José‐Luis Maldonado Prof. Dr. Remi Chauvin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):14186-14195
The synthesis, crystal and electronic structures, and one‐ and two‐photon absorption properties of two quadrupolar fluorenyl‐substituted tetraphenyl carbo‐benzenes are described. These all‐hydrocarbon chromophores, differing in the nature of the linkers between the fluorenyl substituents and the carbo‐benzene core (C?C bonds for 3 a , C?C?C?C expanders for 3 b ), exhibit quasi–superimposable one‐photon absorption (1PA) spectra but different two‐photon absorption (2PA) cross‐sections σ2PA. Z‐scan measurements (under NIR femtosecond excitation) indeed showed that the C?C expansion results in an approximately twofold increase in the σ2PA value, from 336 to 656 GM (1 GM=10?50 cm4 s molecule?1 photon?1) at λ=800 nm. The first excited states of Au and Ag symmetry accounting for 1PA and 2PA, respectively, were calculated at the TDDFT level of theory and used for sum‐over‐state estimations of σ2PA(λi), in which λi=2 hc/Ei, h is Planck’s constant, c is the speed of light, and Ei is the energy of the 2PA‐allowed transition. The calculated σ2PA values of 227 GM at 687 nm for 3 a and 349 GM at 708 nm for 3 b are in agreement with the Z‐scan results. 相似文献
16.
Dr. Céline Le Droumaguet Aude Sourdon Dr. Emilie Genin Dr. Olivier Mongin Dr. Mireille Blanchard‐Desce 《化学:亚洲杂志》2013,8(12):2984-3001
A series of octupolar fluorophores built from a triphenylamine (TPA) core connected to electron‐withdrawing (EW) peripheral groups through conjugated spacers has been synthesized. Their photoluminescence, solvatochromism, and two‐photon absorption (2PA) properties were systematically investigated to derive structure–property relationships. All derivatives exhibit two 2PA bands in the 700–1000 nm region: a first band at low energy correlated with a core‐to‐periphery intramolecular charge transfer that leads to an intense 1PA in the blue‐visible range, and a second more intense band at higher energy due to an efficient coupling of the branches through the TPA core. Increasing the strength of the EW end groups or the length of the conjugated spacers and replacing triple‐bond linkers with double bonds induces both enhancement and broadening of the 2PA responses, thereby leading to cross‐sections up to 2100 GM at peak and higher than 1000 GM over the whole 700–900 nm range. All derivatives exhibit intense photoluminescence (PL) in low‐ to medium‐polarity environments (with quantum yields in the 0.5–0.9 range) and display a strong positive solvatochromic behavior (with Lippert–Mataga specific shifts ranging from 15 000 to 27 500 cm?1), triple bonds, and phenyl moieties in the conjugated spacers, thereby leading to larger sensitivities than those of double bonds and thienyl moieties. More hydrophilic derivatives were also shown to be biocompatible, to retain their 2PA and PL properties in biological conditions, and finally to be suitable as polarity sensors for multiphoton cell imaging. 相似文献
17.
Shanmugam Easwaramoorthi Dr. Jae‐Yoon Shin Sung Cho Dr. Pyosang Kim Yasuhide Inokuma Eiji Tsurumaki Atsuhiro Osuka Prof. Dr. Dongho Kim Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(44):12005-12017
Donor–acceptor systems based on subporphyrins with nitro and amino substituents at meta and para positions of the meso‐phenyl groups were synthesized and their photophysical properties have been systematically investigated. These molecules show two types of charge‐transfer interactions, that is, from center to periphery and periphery to center depending on the peripheral substitution, in which the subporphyrin moiety plays a dual role as both donor and acceptor. Based on the solvent‐polarity‐dependent photophysical properties, we have shown that the fluorescence emission of para isomers originates from the solvatochromic, dipolar, symmetry‐broken, and relaxed excited states, whereas the non‐solvatochromic fluorescence of meta isomers is of the octupolar type with false symmetry breaking. The restricted meso‐(4‐aminophenyl) rotation at low temperature prevents the intramolecular charge‐transfer (ICT)‐forming process. The two‐photon absorption (TPA) cross‐section values were determined by photoexcitation at 800 nm in nonpolar toluene and polar acetonitrile solvents to see the effect of ICT on the TPA processes. The large enhancement in the TPA cross‐section value of approximately 3200 GM (1 GM=10?50 cm4 s photon?1) with donor–acceptor substitution has been attributed to the octupolar effect and ICT interactions. A correlation was found between the electron‐donating/‐withdrawing abilities of the peripheral groups and the TPA cross‐section values, that is, p‐aminophenyl>m‐aminophenyl>nitrophenyl. The increased stability of octupolar ICT interactions in highly polar solvents enhances the TPA cross‐section value by a factor of approximately 2 and 4, respectively, for p‐amino‐ and m‐nitrophenyl‐substituted subporphyrins. On the other hand, the stabilization of the symmetry‐broken, dipolar ICT state gives rise to a negligible impact on the TPA processes. 相似文献
18.
Dr. Atsuro Takai Dr. Daisuke Sakamaki Prof. Dr. Shu Seki Dr. Yoshitaka Matsushita Dr. Masayuki Takeuchi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(22):7385-7388
A new naphthalenediimide (NDI) molecule, where two ferrocene (Fc) units were directly attached to both imide nitrogens ( Fc‐NDI‐Fc ), was synthesized. The Fc units provide high crystallinity to Fc‐NDI‐Fc with good solubility to conventional organic solvents. The Fc units also work as electron‐donating substituents, in contrast to the electron‐deficient NDI unit, resulting in broad charge‐transfer absorption of Fc‐NDI‐Fc from the UV region to 1500 nm in the solid state. The crystal structure analysis revealed that Fc‐NDI‐Fc formed a segregated‐stack structure. The DFT calculation based on the crystal structure showed that the NDI π‐orbitals extended over two axes. The extended π‐network of the NDI units led to the electron‐transport properties of Fc‐NDI‐Fc , which was confirmed using a flash‐photolysis time‐resolved microwave conductivity technique. 相似文献
19.
Extending Metal‐to‐Polyoxometalate Charge Transfer Lifetimes: The Effect of Heterometal Location 下载免费PDF全文
Elliot N. Glass Dr. John Fielden Dr. Alexey L. Kaledin Dr. Djamaladdin G. Musaev Prof. Dr. Tianquan Lian Prof. Dr. Craig L. Hill 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(15):4297-4307
In an effort to develop robust molecular sensitizers for solar fuel production, the electronic structure and photodynamics of transition‐metal‐substituted polyoxometalates (POMs), a novel class of compound in this context, was examined. Experimental and computational techniques including femtosecond (fs) transient absorption spectroscopy have been used to study the cobalt‐containing Keggin POMs, [CoIIW12O40]6? ( 1 a ), [CoIIIW12O40]5? ( 2 a ), [SiCoII(H2O)W11O39]6? ( 3 a ), and [SiCoIII(H2O)W11O39]5? ( 4 a ), finding the longest lived charge transfer excited state so far observed in a POM and elucidating the electronic structures and excited‐state dynamics of these compounds at an unprecedented level. All species exhibit a bi‐exponential decay in which early dynamic processes with time constants in the fs domain yield longer lived excited states which decay with time constants in the ps to ns domain. The initially formed states of 1 a and 3 a are considered to result from metal‐to‐polyoxometalate charge transfer (MPCT) from CoII to W, while the longer‐lived excited state of 1 a is tentatively assigned to a localized intermediate MPCT state. The excited state formed by the tetrahedral cobalt(II) centered heteropolyanion ( 1 a ) is far longer‐lived (τ=420 ps in H2O; τ=1700 ps in MeCN) than that of 3 a (τ=1.3 ps), in which the single CoII atom is located in a pseudo‐octahedral addendum site. Short‐lived states are observed for the two CoIII‐containing heteropolyanions 2 a (τ=4.4 ps) and 4 a (τ=6.3 ps) and assigned solely to O→CoIII charge transfer. The dramatically extended lifetime for 1 a versus 3 a is ascribed to a structural change permitted by the coordinatively flexible central site, weak orbital overlap of the central Co with the polytungstate framework, and putative transient valence trapping of the excited electron on a single W atom, a phenomenon not noted previously in POMs. 相似文献
20.
Multicolored‐Fluorescence Switching of ICT‐Type Organic Solids with Clear Color Difference: Mechanically Controlled Excited State 下载免费PDF全文
Dr. Yujian Zhang Dr. Kai Wang Guilin Zhuang Prof. Zengqi Xie Prof. Cheng Zhang Prof. Feng Cao Prof. Guoxiang Pan Haifeng Chen Prof. Bo Zou Prof. Yuguang Ma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2474-2479
A donor–acceptor‐type fluorophore containing a twisted diphenylacrylonitrile and triphenylamine has been developed by using the Suzuki reaction. The system indicates typical intramolecular charge‐transfer properties. Upon mechanical grinding or hydrostatic pressure, the fluorophore reveals a multicolored fluorescence switching. Interestingly, a fluorescence color transition from green to red was clearly observed, and the change of photoluminescent (PL) wavelength gets close to 111 nm. The mechanisms of high‐contrast mechanochromic behavior are fully investigated by techniques including powder XRD, PL lifetime, high‐pressure PL lifetime, and Raman spectra analysis. The tremendous PL wavelength shift is attributed to gradual transition of excited states from the local excited state to the charge‐transfer state. 相似文献