光致变色冠醚部花菁染料的合成及其逆光致变色性

作者用含冠醚结构单元的2-甲基-苯并噻唑季铵盐与取代水物醛缩合得到了五个光致变色冠醚部化菁化合物。这些新的冠醚化合物具有逆光致变色性质, 较稳定的结构是开环部花菁式。     

Excited-state dynamics of spiropyran-derived merocyanine isomers

Merocyanine (MC) isomers that are formed after absorption of a UV photon by 1',3'-dihydro-1',3'-3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2',2'-(2H)-indole] were studied. Several, predominantly TTC and TTT, merocyanine isomers are present in toluene solution ("T" and "C" indicate trans and cis conformations of the C-C bonds in the methine bridge). Excitation in the MC visible absorption band (at 490, 550, and 630 nm) with 100 fs laser pulses was used to study MC excited-state dynamics. Internal conversion on the picosecond time scale was found to be the dominant relaxation pathway. Excited-state isomerization reactions were also observed. Excitation at 630 nm (assigned to TTC isomer excitation) leads to formation of a third isomer (either CTC or CTT). Excitation at 490 nm (assigned to TTT isomer excitation) leads to more complex excited-state relaxation, including formation of two isomers: TTC (absorption at 600 nm) and CTC or CTT (absorption at 650 nm).     

Synthesis and spectroscopic properties of a novel zinc phthalocyanine with four 17-membered crown ether voids

A novel zinc phthalocyanine containing four 17-crown-5 ether voids(17C5ZnPc) has been synthesized and characterized. UV-visible absorption and fluorescence emission spectra and as-sociated photophysical parameters have been determined. In contrast to most of the crown ether substituted phthalocyanines, no cofacial dimer formation is observed in the presence of alkali metal salts. In addition to the fluorescence at 710 nm from S1, a strong upper excited state (Soret 52) emission around 424 nm has been detected for the first time in the phthalocyanine series. Fluorescence decay of S1 and S2 emission can be analyzed by mono- and biexponential fits respectively. X-ray structure analysis showed that the crown ether unit is conformationally deformed and oblate that may account for the unusual spectroscopic properties.     

NANOSECOND LASER PHOTOLYSIS OF RHODOPSIN AND ISORHODOPSIN

Kinetic and spectral measurements have been carried out on the primary intermediate in the photolysis of rhodopsin and isorhodopsin, initiated by a 457 nm, 6 ns (FWHM) laser pulse. In rhodopsin the kinetic decay of bathorhodopsin was found to be 140 ± 15 ns at 20°C. The decay of bathorhodopsin to lumirhodopsin has an activation energy of 51 ± 4 kJ/mol (12.2 ± 1 kcal/mol). The decay kinetics of bathorhodopsin were found to be the same for rhodopsin in membrane and detergent solubilized suspensions. The kinetic decay of the batho product in the photolysis of isorhodopsin was found to be the same as rhodopsin.
The corrected transient spectrum 50 ns following excitation in rhodopsin has two peaks near 560 and 440 nm. A peak was also observed in isorhodopsin near 550 nm at 50 ns following excitation but no transient was observed in the blue. The 550 nm peak in isorhodopsin has an intensity similar to that in rhodopsin indicating that the quantum yields for the formation of batho products of rhodopsin and isorhodopsin are similar under the irradiation conditions used here. Transient spectra for rhodopsin and isorhodopsin 1 μs following excitation are also different. In isorhodopsin the corrected transient spectrum has a peak at 500 nm, similar to low temperature steady state irradiation spectra. The 1 μs transient spectrum in rhodopsin is more intense than in isorhodopsin and shows a peak at 475 nm.     

Production and excited state dynamics of the photorearranged isomer of benzyl chloride and its methyl derivatives studied by stepwise two-color laser excitation transient absorption and time-resolved thermal lensing techniques

Production and photoexcited dynamics of reaction intermediates with photolyses of benzyl chloride (BzCl) and methyl-substituted benzyl chlorides (MeBzCls) were studied by using stepwise two-color laser excitation transient absorption (TC-TA) and two-color laser excitation time-resolved thermal lensing (TC-TRTL) measurements. With photoexcitation of BzCl the formation of transient photorearranged isomer was suggested in the previous paper [Res. Chem. Intermed. 2001, 27, 137]. Such an isomer formation for MeBzCls was also observed in a 248 nm excitation. It was found that further photoexcitation of the isomers with the 308 nm light caused photodissociation to yield the corresponding benzyl radicals. The reaction quantum yield and the molar absorptivity of the photorearranged isomer of BzCl were estimated. The heat of reaction for the photodissociation of the isomer was successfully determined with the TC-TRTL measurement. These experimental results were consistent with MO calculations.     

Femtosecond to Subnanosecond Multistep Calcium Photoejection from a Crown Ether‐Linked Merocyanine

Photoinduced calcium release from the crown ether‐linked merocyanine DCM–crown is reexamined by femtosecond transient absorption spectroscopy with sub‐100 fs time resolution. Photodisruption of the bond linking the cation to the nitrogen atom shared by the crown and the chromophore is found to take place in 130 fs. Confirming our previous reports, the photoinduced intraligand charge transfer is observed in the picosecond regime but kinetics involving three‐components (1 ps, 8 ps and 77 ps), together with a 56 ps stimulated‐emission time‐resolved red shift, are found in the present study. Both delayed intraligand charge transfer and cation release are assumed to occur in this time range due to repulsion effects between the positively charged nitrogen of the crown ether moiety and the cation. In the subnanosecond regime, a 670 ps time‐resolved red shift of the stimulated‐emission spectrum of the charge‐transfer state, similar to the shift previously observed with Sr²⁺, demonstrates the motion of the cation away from the crown to the bulk. A thorough examination of the present data allows us to conclude that calcium ion is photoejected to the bulk in a multistep process.     

On the photochromism of spiro

The recently synthesized spiro[cyclohexadiene-dihydroacridines] consisting of perpendicularly arranged aroylcyclohexadiene and N -methyl-dihydroacridine moieties were found to have photochromic properties. The reversible photoisomerization from the spiro compound toward a colored merocyanine caused by C–C bond cleavage in the cyclohexadiene was studied by stationary and time-resolved measurements of their optical spectra. The course of the absorption under UV and visible irradiation, respectively, and HPLC analysis of the photoproducts result in the determination of excitation energy-dependent quantum yields for the merocyanine formation and, in reverse, the ring closure, as well as degradation. Whereas the thermal back reaction completely recovers the spiro compound ( k ∼ 6.8 × 10⁻⁴ s⁻¹, T = 22°C), degradation of the merocyanine under irradiation at 480 nm has a probability of about 6%. Picosecond-resolved measurements of the fluorescence and the transient absorption show that photoisomerization occurs via the first excited singlet state within 100 ps depending on the activation barrier.     

Crown-containing spironaphthoxazines and spiropyrans. 2. Influence of metal cations on the photochromic properties of spironaphthoxazines linked with aza-15(18)-crown-5(6) ethers

Spironaphthoxazines linked with aza-15(18)-crown-5(6) fragments were synthesized and studied for the first time. Addition of alkaline-earth cations to solutions of crown-containing spironaphthoxazines causes a hypsochromic shift of the absorption band of the spiro form and a bathochromic shift of the absorption band of the merocyanine form, shifts the equilibrium to the merocyanine form, and changes the lifetime of the photoexcited merocyanine form. The spectral and kinetic data were used to propose a mechanism of complexation and calculate the stability constants of the resulting complexes. The complexation involves the crown fragment and the merocyanine oxygen atom. The type of the complex is determined by the cation nature and size.     

Formation and relaxation dynamics of iso-CH2Cl-I in cryogenic matrices

Photolysis of chloroiodomethane (CH(2)ClI) in cryogenic matrices followed by recombination of the nascent radical pair produces an isomer (CH(2)Cl-I) that features a halogen-halogen (Cl-I) bond. Using ultrafast laser pulses, it is possible to follow the formation of this isomer by transient electronic absorption in low-temperature matrices of N(2), CH(4), and Ar. Frequency-domain measurements provide vibrational and electronic spectra, and electronic structure calculations give the structures of the isomers and the minimum energy path that connects them. The ultrafast experiments cleave the C-I bond with a 267-nm photolysis pulse and probe the formation of the isomer at wavelengths between 435 nm and 510 nm. The longest wavelengths preferentially interrogate vibrationally excited molecules, and their transient absorption shows that the highly vibrationally excited isomer appears within 1 to 2 ps, depending on the matrix, likely reflecting the loss of 2000 cm(-1) or more of energy in a strong, inelastic collision of the fragments with the matrix. The subsequent relaxation of the vibrationally excited isomer occurs in 20 to 40 ps, a time that is comparable to those observed for halomethane molecules and their isomers in liquids and in supercritical CO(2). These observations suggest that the formation and initial relaxation of the isomer in dense media do not depend strongly on the identity of the surroundings.     

The role of the πσ* state in intramolecular charge transfer of 4-(dimethylamino)benzonitrile

The solvent-polarity dependence and temporal characteristics of the transient absorption of 4-(dimethylamino)benzonitrile, DMABN, and 4-(dimethylamino)benzethyne, DMABE, demonstrate the presence of the πσ*-state absorption at about 700 nm and the ππ* (LE)-state absorption at about 520 nm and 450 nm. The rise and decay times of the πσ*-state transient differ from those of the ππ*-state transients in both compounds. Moreover, the peak position of the πσ*-state absorption is blue-shifted and more intense in acetonitrile as compared to n-hexane, whereas the band positions of the ππ*-state absorptions are essentially the same in the two solvents. For DMABN in acetonitrile, the rise time (～4.3 ps) of the twisted intramolecular charge transfer (TICT)-state transient at 330 nm is identical to the decay time of the πσ*-state transient. The 4.8 ns decay time of the TICT-state absorption of DMABN is longer than the 2.9 ns decay time of the intramolecular charge-transfer (ICT) fluorescence, indicating that the fluorescent ICT state differs from the TICT state observed in transient absorption. These results are consistent with the presence of a low-lying πσ* state in DMABN (and DMABE), and the role the πσ* state plays in the formation of the TICT state of DMABN.     

Synthesis of cyanine dyes derived from benzotellurazo‐15‐crown‐5

A series of crown ether cyanine dyes including crown ether styryl cyanine dyes, crown ether merocyanine dyes and crown ether squarylium cyanine dyes (unsymmetric and symmetric) derived from key intermediate 2‐methyl‐5,6(15‐crown‐5)benzotellurazole ( 1 ) were prepared.     

Direct observation of a 1MLCT state by ultrafast transient absorption spectroscopy in Mo2(O2C-9-anthracene)4

We have observed the excited-state dynamics of Mo2(O2C-9-anthracene)4 in THF using ultrafast transient UV/vis absorption spectroscopy. Following excitation at 514.5 nm into the metal-to-ligand charge-transfer (MLCT) state, transient absorption bands of the 1MLCT state appear at 410 and 610 nm. We assign these features to the 1MLCT state, which has a lifetime of approximately 10 ps. The decay of 1MLCT is accompanied by the formation of the triplet 3MLCT state, with an absorption band peaking at 410 nm. Excitation at 347 nm populates directly the ligand-centered (LC) state. From the rise of the 1MLCT band, the lifetime of the 1LC state is estimated to be less than 1 ps.     

Synthesis and photochromism of spirobenzopyran derivatives bearing an oxymethylcrown ether moiety: metal ion-induced switching between positive and negative photochromisms

Spirobenzopyran derivatives carrying an oxymethylcrown ether moiety were synthesized, and their photochromism was studied in the presence of various metal ions in acetonitrile. The metal ion complexing ability of the crown ether moiety in crowned spirobenzopyrans affects both thermal isomerization and photoisomerization of their spirobenzopyran moiety to a great extent. When the interaction of the crown ether moiety with a metal ion was strong enough to cause thermal isomerization of the spirobenzopyran moiety to its corresponding merocyanine form and to suppress UV-induced isomerization to the merocyanine form, a negative photochromism appears. On the other hand, a relatively weak interaction of the crown ether moiety with a metal ion affords a positive photochromism. This phenomenon enables us to switch the photochromic behavior between positive and negative photochromisms.     

Properties of cis- and trans-bis(crown ether)s for complexation and extraction of alkali metal picrates

The properties of cis- and trans-bis(crown ether)s containing benzo-15-crown-5 or benzo-18-crown-6 units as complexants and extractants for alkali metal picrates have been studied. The optical spectra suggest that the cis-bis(crown ether)s can form intramolecular 2:1 crown ether unit/cation complexes with particular metal cations easily, while the trans-bis(crown ether)s can form only 1:1 crown ether unit/cation complexes because of the unfavourable trans configuration for the formation of the 2:1 complexes. It was found that the cis isomer possesses much higher extractive power than the trans isomer for the metal cations, which also reflects their complexing properties. The extraction equilibrium constants and thermodynamic quantities have been also evaluated, and the effect of the stereochemical structure of the bis(crown ether) on the complexing and extractive properties is discussed.     

Spectral kinetic characteristics of the photoisomerization products of naphthylmethylideneiminospironaphthopyran induced by photolysis at different wavelengths

The spectral kinetic characteristics of intermediates generated by photolysis with light at the wavelengths 337 and 430 or 470 nm of the photobifunctional compound (PBC), 1,3-dihydro-5-(2-hydroxy-1-naphthylmethylideneimino)-1,3,3-trimethylspiro[2H-indole-2,3-[3H]-naphtho[2,1-b]pyran], whose molecule combines the spironaphthopyran and hydroxyazomethine fragments, and also parameters of model compounds, viz., naphthylmethylideneimine and spironaphthopyran, were studied in methanol and toluene. The relative quantum yields of formation of different intermediates of PBC were measured relatively to model compounds, namely, trans-keto isomer formed due to cis-trans-isomerization and prototropic equiliration in the azomethine fragment, and in the merocyanine form generated by spiro bond opening. It was found that the photolysis of the PBC with light at the wavelengths ?? = 430 or 470 nm nearly no produces the merocyanine form, whereas the relative yield of the trans-keto tautomer is ??0.6. For PBC photolysis at ?? = 337 nm, the yield of the merocyanine form is ??0.2 and the yield of the trans-keto isomer decreases substantially (??0.2). The solvent nature affects the kinetic behavior of the system. The consistency of the isomerization and proton transfer processes is discussed.     

Ultrafast UV-mid-IR investigation of the ring opening reaction of a photochromic spiropyran

We present a femtosecond UV-mid-IR pump-probe study of the photochemical ring-opening reaction of the spiropyran 1',3',3',-trimethylspiro-[-2H-1-benzopyran-2,2'-indoline] (also known as BIPS) in tetrachloroethene, using 70 fs UV excitation pulses and probing with 100 fs mid-IR pulses. The time evolution of the transient IR absorption spectrum was monitored over the first 100 ps after UV excitation. We conclude that the merocyanine product is formed with a 28 ps time constant, contrasting with a 0.9 ps time constant obtained in previous investigations where the rise of absorption bands at visible wavelengths were associated with product formation. We deduce from the observed strong recovery of the spiropyran IR absorption bleaches that, in tetrachloroethene, the main decay channel for the S(1) excited state of the spiropyran BIPS, is internal conversion to the spiropyran S(0) state with a quantum yield of > or = 0.9. This puts an upper limit of 0.1 to the quantum yield of the photochemical ring-opening reaction.     

Femtosecond Spectroscopic Studies on the Red Light-Absorbing Form of Oat Phytochrome and 2,3-Dihydrobiliverdin

Abstract— The excited state behavior of the red light-absorbing form of phytochrome (Pr) was studied on the femtosecond time scale. After excitation of Pr with 75 fs laser pulses at 616 nm the kinetics of the transient absorption changes was recorded at selected wavelengths probing mainly the bleaching of the Pr ground-state absorption and the stimulated emission. The kinetic data obtained indicate the population of an excited state with a 3 ps lifetime immediately after excitation. This state precedes the formation of another excited state with a 32 ps lifetime. The decay of the latter state is followed by the appearance of a first product state that is assumed to represent lunii-R. In addition, 2,3-dihydrobiliverdin, which is considered to be an adequate model of the Pr chro-mophore, was included in the femtosecond studies. The absorption difference spectra recorded at various delay times show an immediate bleaching of the ground-state absorption. Simultaneously with bleaching a broad transient absorption appears between 410 and 525 nm. The data analysis yields similar kinetic components as they were observed in the decay of Pr. It is suggested from this finding that within the first tens of picoseconds after excitation the excited-state properties of Pr are mainly determined by the properties of the chromophore itself.     

CEYSTAL STRUCTURE OF EXTRACTED COMPLEX OF URANYL CHLORIDE WITH DICYCLOHEXYL-18-CROWN-6(MIXED ISOMERS),UO_2Cl_4]_3 [C_(20)H_(36)O_6- (ISOMER A)-H_3O]_4 [C_(20)H_(36)O_6(ISOMER B)-H_3O]_2

<正> Mr= 3584.7, monoclinic, P21/c, a = 14.647(2), b = 20.333(2), c = 25.759(3) A, β= 91.05(1)°, Z = 2, V = 7670.1 A3, Dc = 1.544 g/cm3,μ=32.629 cm-1, R=0.056 for 4207 observed reflections. Each asymmetric unit consists of two UO2Cl42- complex anions and three C20B36O6-H3O+ complex cations. In two of the complex cations (isosaer A), HaO+ cation is anchored in each crown ether ring by three stronger hydrogen bonds. In another complex cation (isomer B) only two stronger hydronger bonds are formed between the H3O+ cation and crown ether. The third hydrogen bond is very weak.     

Prolongation of the lifetime of the charge-separated state at low temperatures in a photoinduced electron-transfer system of [60]fullerene and ferrocene moieties tethered by rotaxane structures

A rotaxane tethering both fullerene (C60) and ferrocene (Fc) moieties (abbreviated as (C60;Fc)rotax+) was synthesized in a good yield by the urethane end-capping of pseudorotaxane based on the crown ether-secondary amine motif. In (C60;Fc)rotax+, the C60 group serving as an electron acceptor is attached to the crown ether wheel, through which the axle with a Fc group acting as an electron donor on its end penetrates. The intrarotaxane photoinduced energy-transfer and electron-transfer processes between C60 and Fc in (C60;Fc)rotax+ have been investigated by time-resolved transient absorption and fluorescence measurements with changing solvent polarity. Nanosecond transient absorption measurements of the rotaxane demonstrated that the charge-separated state (C60*-;Fc*+)rotax+ is formed mainly via the excited triplet state of C60 in polar solvents. The lifetime of (C60*-;Fc*+)rotax+ was evaluated to be 20 ns in dimethylformamide (DMF) at room temperature. With lowing temperature, the lifetime of (C60*-;Fc*+)rotax+ extends to 270 ns in DMF at -65 degrees C, due to the structural changes leaving C60*- and Fc*+ at a relatively long distance in the low-temperature region.     

Electronic and infrared absorption spectra of linear and cyclic C6+ in a neon matrix

Electronic and infrared absorption spectra of mass-selected C6+, generated by dissociative electron impact ionization of C6Cl6 and C6Br6, have been recorded in 6 K neon matrices. Linear and cyclic forms of C6+ have been observed. The 2Pig<--Chi2Piu electronic transition of linear C6+ has its origin band at 646 nm whereas for the (2) 2B2<--Chi2A1 system of the cyclic isomer it lies at 570 nm. An infrared active fundamental mode in the ground electronic state of C6+ is observed at 2092 and 1972 cm(-1) for the linear and cyclic isomer, respectively.