Ultrafast ring opening reaction of a photochromic indolyl-fulgimide

The photo-induced ring-opening reaction C → E of a photochromic indolyl-fulgimide is investigated by sub-picosecond pump–probe spectroscopy in the visible and infrared spectral range. The thermally stable C-isomer shows a pronounced absorption in the visible spectral range without spectral overlap with the absorption of the E- and Z-isomer. The comparison of infrared and visible transient absorption data allows to assign the observed exponential 2.1 ps dynamics to the ring-opening reaction and the non-exponential 10–40 ps component to the cooling of the hot molecules. The transient absorption spectra taken 80 ps after photo-excitation are identical with the steady state difference spectra.     

Detailed investigation on a negative photochromic spiropyran

The negative photochromic properties of a spiropyran are investigated in various solvents and in solutions of different acidity. The results indicate that the polarity of the solvent has a prominent effect on λ_max of the coloured merocyanine form (MC), whereas its effects on λ_max of the closed form (SP) and on the coloration rates after visible bleaching are very weak. From the effect of acid concentration on the coloration rates the pK_a of the cis intermediate Y in the coloration process is determined to be about 1.1 lower than that of the protonated merocyanine (MCH⁺). The structures and configurations of MC, SP, MCH⁺ and Y are assigned via their ¹H NMR spectra.     

Electrochemical investigation of a photochromic spiropyran containing a pyrrolidinofullerene moiety

Reversible transformations of a hybrid molecule based on [60]fullerene and a spiropyran moiety under conditions of combined photo- and electrochemical exposure were found. It has been established that the electrochemical oxidation of the UV-photoinduced colored form of the hybrid spiropyran in solution significantly accelerates the discoloration process and does not affect the fullerene part of the hybrid molecule. The research results are promising for designing a photo-electrochromic device that modulates electromagnetic radiation in the visible range of the spectrum.     

Photoswitched DNA-binding of a photochromic spiropyran

The dramatically different DNA-binding properties of the two isomeric forms of a photochromic spiropyran have been demonstrated, enabling photoswitched DNA binding. The closed, UV-absorbing form shows no signs of interaction with DNA. Upon UV exposure the spiropyran is isomerized to the open form that binds to DNA by intercalation. The process is fully reversible as the corresponding dissociation process is induced by visible light.     

Light-induced cytotoxicity of a photochromic spiropyran

In this work we present a novel water soluble spiropyran photoswitch that can be photonically activated inside live cells from a form that has no significant effect on the cellular survival to a form that induces a dramatic toxic response.     

A semiclassical molecular dynamics of the photochromic ring-opening reaction of spiropyran

The photochromic ring-opening reaction of spiropyran(SP) has been investigated by a realistic semiclassical dynamics simulation,accompanied by SA3-CASSCF(12 10)/MS-CASPT2 potential energy curves(PECs) of S0–S2.The main simulation results show the dominate pathway corresponds to the ringopening process of trans-SP to form the most stable merocyanine(MC) product.These findings provide more important complementarity for interpreting experimental observations.     

Ultrafast bidirectional photoswitching of a spiropyran

We report on bidirectional photochemical switching of 6,8-dinitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] (6,8-dinitro-BIPS) between the ring-closed spiropyran and the ring-open merocyanine form. This is studied by femtosecond three-color pump-repump-probe experiments. Both ring opening and ring closure are photoinduced. Completion of an entire cycle, consisting of opening and subsequent closure, can be achieved within 40 ps. A much shorter time (<6 ps) is needed for the converse cycle, consisting of initial ring closure and subsequent ring opening. Furthermore, we perform pump-probe experiments with ultraviolet/visible pump and visible/mid-infrared probe pulses for an unambiguous spectroscopic identification of the open and closed molecular forms. Following visible excitation of the ring-open molecules, ultrafast ring closure is observed directly in the mid-infrared. The quantum efficiencies for ring opening and ring closure starting from the respective equilibirum states are determined to be approximately 9% and 40%. These results show that 6,8-dinitro-BIPS is an ultrafast bidirectional molecular switch exhibiting a high quantum efficiency.     

Structure of a new photochromic indoline spiropyran

Conclusions An x-ray diffraction structural study was carried out for the photochromic spirpyran 1,3,3-trimethyl-5-nitrospiro(indoline-2,2-[2H-1]-benzopyran). The C_spiro-O bond in the spiropyran is longer than the normal value but shorter than in the isomeric spiropyran with the nitro group in the benzopyran fragment, which is characterized by a higher quantum yield.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 191–194, January, 1985.     

Ultrafast dynamics of a spiropyran in water

The reversible switching of a water-soluble spiropyran compound is recorded over 1 ns by means of femtosecond vis-pump/vis- and IR-probe spectroscopy under aqueous conditions. Our investigations reveal that the photochemical conversion from the closed spiropyran to the open merocyanine takes 1.6 ps whereas the reversed photoreaction is accomplished within 25 ps. The combination of time-resolved and steady-state observations allows us to reveal central parts of the reaction pathway leading to either form. The enhanced water solubility, its fast and efficient switching behavior, and its stability against hydrolysis over a time range of several weeks make this compound an attractive and versatile tool for biological applications.     

Ultrafast electrocyclic ring opening in previtamin D photochemistry

Photochemical reactions of 7-dehydrocholesterol and lumisterol were studied by nanosecond and picosecond UV laser excitation. The resulting production of previtamin D and tachyslerol was analysed by chromatography. With picosecond excitation, the formation of the secondary product tachysterol was significantly reduced. Model calculations gave reactive and non-reactive rate constants for 7-dehydrocholesterol and lumisterol.     

Ultrafast ring-closure reaction of photochromic indolylfulgimides studied with UV-pump-IR-probe spectroscopy

The ring-opening and ring-closure reactions of a photochromic indolylfulgimide are investigated with femtosecond vibrational spectroscopy. Spectral signatures due to excited-state decay and vibrational cooling are seen in the mid-IR region. For the ring-opening reaction triggered with visible pulses, a lifetime of the excited electronic state of 4 ps was obtained in polar solution. In a nonpolar solvent, this time constant is reduced to 2 ps. The ring-closure reaction induced with UV pulses displays an excited-state lifetime and thus a building of the photoproduct of roughly 0.5 ps. For all processes, the subsequent cooling occurs on a 15-ps time scale lasting up to approximately 50 ps. The time-resolved IR measurements do not support the existence of any long-living intermediate states.     

Ultrafast formation of transients in spiropyran photochromism

Transient absorption spectra in the photocolouration and photobleaching of the indoline 6-nitrosubstituted spiropyran have been investigated with picosecond spectroscopy. The cis—cisoid intermediate stereoisomer at 440 nm and some of the final coloured forms are produced in less than 10 ps in the photocolouration.     

Synthesis and characterization of coumarin-based spiropyran photochromic colorants

Two coumarin-based spiropyran derivatives were synthesized and characterized in two steps to explore their photochromic properties. Both prepared compounds are sensitive to UV light and change colors upon irradiation. The resulting photogenerated zwitterions revert to the original compounds while being heated. A new family of organic photochromic colorants is introduced.     

Ultrafast ring opening in 1,3-cyclohexadiene investigated by simplex-based spectral unmixing

We use spectral unmixing to determine the number of transient photoproducts and to track their evolution following the photo-excitation of 1,3-cyclohexadiene (CHD) to form 1,3,5-hexatriene (HT) in the gas phase. The ring opening is initiated with a 266 nm ultraviolet laser pulse and probed via fragmentation with a delayed intense infrared 800 nm laser pulse. The ion time-of-flight (TOF) spectra are analyzed with a simplex-based spectral unmixing technique. We find that at least three independent spectra are needed to model the transient TOF spectra. Guided by mathematical and physical constraints, we decompose the transient TOF spectra into three spectra associated with the presence of CHD, CHD(+), and HT, and show how these three species appear at different times during the ring opening.     

A new ring opening reaction of N-aminophthalimide hydrazones

Araldehyde hydrazones III of N-aminophthalimide underwent rapid ring opening reactions initiated by the addition of excess base to their refluxing methanolic solutions. The products were conveniently isolated through liquid-liquid extraction as the stable sodium salts V, and acidification precipitated the resulting phthalic acid congeners VI from aqueous solution. Compounds III readily exchanged one hydrazine moiety for another. For example, IIId reacted with 2,4-dinitrophenylhydrazine to give the 2,4-dinitrophenylhydrazone of 4-chlorobenzaldehyde (VIId, 93%). Nonetheless, IIIg reacted exclusively at the carboxaldehyde function to give products VIIIa and VIIIb.     

UV-induced self-assembly of the inclusion complexes formed between a long-chain photochromic spiropyran and cyclodextrins

Photochromic spiropyran with a long chain alkyl substitute can form axial complexes with α-, β-, and γ-cyclodextrin, respectively. The complexes show normal photochromism. The novel property of the colored forms of the inclusion complexes is that they can assemble into dimers at relatively low concentration or J-aggregates at relatively high concentration. For α-, β-, and γ-cyclodextrin, λ_(max) of the J-aggregates appear at 700 650, and 630 nm, respectively. The sizes of the cavities of cyclodextrins have very little effect on the spectra and decoloration kinetics of the dimers, but have great effects on the spectra of the J-aggregates. Unlike the charge transfer complex of Krongauz, the decoloration process of the dimers or J-aggregates cannot be described by an exponential or a two-exponential kinetics, but obey half-order kinetics very well. Another result that can be deduced from the kinetic analysis is that unlike the dimers formed in apolar solvents or in polymers, which consist of a color     

Use of photochromic spiropyran as a molecular probe of large strain in polycarbonate

The effect of tensile deformation of polycarbonate on the kinetics of the decoloration reaction of photochromic spiropyran dissolved in the polymer was studied. It was shown that the strain-induced change in the decoloration rate can be used for measurement of the temperature jump appearing during deformation and yielding of the specimen provided that structural and thermodynamic changes in the system are taken into account.     

Isomerization dynamics of photochromic spiropyran molecular switches in phospholipid bilayers

Transient absorption spectroscopy was used to investigate the dynamics of the photochromic indolinobenzospiropyran reaction in toluene solution and in phosphatidylcholine bilayers (1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)). After excitation with UV light, colorless (R/S)-2-(3',3'-dimethyl-6-nitro-3'H-spiro[chromene-2,2'-indol]-1'-yl)ethanol derivatives are converted to colored merocyanine products in high yield; Phi = 0.45 in DMPC liposomes. We find that the reaction occurs in the bilayer aliphatic region in the gel (P(beta)(')) and liquid (L(alpha)) phases. The Arrhenius activation energy for the isomerization in DMPC bilayers was approximately 3.5 times larger in the liquid phase (L(alpha), E(a) = 26.0 +/- 1.0 kJ mol(-1)) than that in the gel phase (P(beta)('), E(a) = 7.3 +/- 1.6 kJ mol(-1)). Analysis of the isomerization rate constant temperature dependence allows an estimation of the bilayer viscosity and free volume properties in the L(alpha) phase.