Two-photon Isomerization Research Articles

Two-photon isomerization properties of donor-acceptor Stenhouse adducts.

Donor-acceptor Stenhouse adducts (DASAs) are important photo-responsive molecules that undergo electrocyclic reactions after light absorption. From these properties, DASAs have received extensive attention as photo-switches with negative photochromism. Meanwhile, several photochemical applications require isomerization events to take place in highly localized volumes at variable depths. Such focused photoreactions can be achieved if the electronic excitation is induced through a non-linear optical process. In this contribution we describe DASAs substituted with extended donor groups which provide them with significant two-photon absorption properties. We characterized the photo-induced transformation of these DASAs from the open polymethinic form to their cyclopentenic isomer with the use of 800 nm femtosecond pulses. These studies verified that the biphotonic excitation produces equivalent photoreactions as linear absorbance. We also determined these DASAs' two-photon absorption cross sections from measurements of their photoconverted yield after biphotonic excitation. As we show, specific donor sections provide these systems with important biphotonic cross-sections as high as 615 GM units. Such properties make these DASAs among the most non-linearly active photo-switchable molecules. Calculations at the TDDFT level with the optimally tuned range-separated functional OT-CAM-B3LYP, together with quadratic response methods indicate that the non-linear photochemical properties in these molecules involve higher lying electronic states above the first excited singlet. This result is consistent with the observed relation between their two-photon chemistry and the onset of their short wavelength absorption features around 400 nm. This is the first report of the non-linear photochemistry of DASAs. The two-photon isomerization properties of DASAs extend their applications to 3D-photocontrol, non-linear lithography, variable depth birefringence, and localized drug delivery schemes.

Picosecond optical vortex-induced chiral surface relief in an azo-polymer film

We report on the first demonstration of picosecond optical vortex-induced chiral surface relief in an azo-polymer film due to two-photon absorption isomerization. The chiral surface relief exhibits an extremely narrow defocusing tolerance without undesired outer rings due to the Airy pattern of highly focused light. Such chiral surface relief reflects a z-polarized electric field with an azimuthal helical phase caused by spin–orbital angular momentum coupling.

System for psychophysical measurements of two-photon vision

Two-photon absorption occurring in photoreceptors of human eye is responsible for perception of pulsed infrared laser beams. Color of perceived light corresponds to about half of wavelength of stimulating beam. This recently discovered phenomenon is called two-photon vision. However it is yet not clear how such phenomena could impact an ophthalmic diagnosis and therefore further studies are required. In this paper we present the system that enables future psychophysical experiments to extend knowledge about two-photon vision and its diagnostic value by identifying differences between two-photon and single-photon vision. Full Text: PDF ReferencesD. A. Atchison, G. Smith, Optics of the human eye (Butterworth-Heinemann 2000) CrossRef G. Palczewska et al. "Human infrared vision is triggered by two-photon chromophore isomerization", Proceedings of the National Academy of Sciences 111, 1428 (2014). CrossRef P. Artal, S. Manzanera, K. Komar, A. Gambín-Regadera, M. Wojtkowski, "Visual acuity in two-photon infrared vision", Optica 4, 1488 (2017). CrossRef K. Komar et al. "Posterior Eye Shape Measurement With Retinal OCT Compared to MRI", Investigative Ophthalmology & Visual Science 57, 196 (2016). CrossRef K. Komar et al. "Two-photon visual sensitivity of human cones - a psychophysical study", Investigative Ophthalmology & Visual Science 59, 4049 (2018). DirectLink S. A. Burns,R.H. Webb, Handbook of optics 28 (New York, McGraw Hill 1994) DirectLink R. W. Nygaard, T. E. Frumkes, "Calibration of the retinal illuminance provided by maxwellian views", Vision Research (1982) CrossRef P. Melillo et al. "Pupillometric analysis for assessment of gene therapy in Leber Congenital Amaurosis patients", Biomedical engineering online 11, 40 (2012) CrossRef P. A. Stanley, A. K. Davies, "The effect of field of view size on steady-state pupil diameter", Ophthalmic and Physiological Optics, 15, 601 (1995) CrossRef S. Mathôt, "Pupil mimicry is the result of brightness perception of the iris and pupil" Journal of Cognition 1 (2018) CrossRef M. M. Thomas, T. D. Lamb, "Light adaptation and dark adaptation of human rod photoreceptors measured from the a‐wave of the electroretinogram", The Journal of physiology 518, 479 (1999) CrossRef

Enhanced Two-Photon Photochromism in Metasurface Perfect Absorbers.

Light switchable materials are essential to optoelectronic applications in photovoltaics, memories, sensors, and communications. Natural switchable materials suffer from weak absorption and slow response times, preventing their use in low-power, ultrafast applications. Integrating light switchable materials with metasurface perfect absorbers offers an innovative route to achieving desirable features for nanophotonic devices, such as directional emission, low-power and broadband operation, high radiative quantum efficiency, and large spontaneous emission rates. Here we show an enhanced two-photon photochromism based on a metasurface perfect absorber: film-coupled colloidal silver nanocubes. The photochromic molecules, spiropyrans, are sandwiched between the silver nanocubes and the gold substrate. With nearly 100% absorption and an accompanying large field enhancement in the molecular junction, the transformation of spiropyrans to merocyanines is observed under excitation with 792 nm laser light. Fluorescence lifetime measurements on the merocyanine form reveal that large Purcell enhancement in the film-coupled nanocubes leads to large enhancements of the spontaneous emission rate and a high quantum efficiency. An averaged incident power as low as 10 μW is enough to initiate the two-photon isomerization of spiropyran in the film-coupled nanocubes, and a power of 100nW is able to excite the merocyanines to emit fluorescence. The power consumption is orders of magnitude lower than bare spiropyran thin films on silicon and gold, which is highly desirable for the writing and reading processes relevant to optical data storage. By sweeping the plasmonic resonance of the film-coupled nanocubes, wavelength specificity is demonstrated, which opens up new possibilities for minimizing the cross talk between adjacent bits in nanophotonic devices.

Two-photon isomerization triggers two-photon-excited fluorescence of an azobenzene derivative

Photoisomerization provides a general means for photo-controlling molecular structure and function, and two-photon induced isomerization has some advantages over one-photon processes. Here, we report the two-photon absorption (TPA) induced optical properties and characteristics of an azobenzene derivative, namely N-(3,4,5-octanoxyphenyl)-N′-4-[(4-hydroxyphenyl)azophenyl]1,3,4-oxadiazole (AOB-t8). With the activation of red light, the photoproduct of cis-AOB-t8 isomers has been unambiguously identified, and the two-photon induced isomerization process of AOB-t8 in THF is characterized with the relevant rate constants of forward and backward reactions. The TPA coefficients and cross-sections of AOB-t8 at different wavelengths, and nonlinear optical refractive index are determined from femtosecond nonlinear optical measurements. Particularly, the results indicate that the two-photon excited emission can be effectively triggered by the two-photon-induced isomerization from trans- to cis-AOB-t8, demonstrating an on-switch from non-fluorescence to visible blue emission. Consistent with the observations from one-photon excitation, we suggest that the enhanced two-photon excited fluorescence of AOB-t8 solution originates from the combined contribution of cis-AOB-t8 monomer and its aggregates, i.e., the conformation transition from trans- to cis-AOB-t8 opens the emission channel and the self-assembly aggregation of cis-AOB-t8 isomers further enhances the fluorescence upon red light excitation.

Two-stage optical recording: photoinduced birefringence and surface-mediated bits storage in bisazo-containing copolymers towards ultrahigh data memory.

Ultrahigh density data storage is in high demand in the current age of big data and thus motivates many innovative storage technologies. Femtosecond laser induced multi-dimensional optical data storage is an appealing method to fulfill the demand of ultrahigh storage capacity. Here we report a femtosecond laser induced two-stage optical storage in bisazobenzene copolymer films by manipulating the recording energies. Different mechanisms can be selected for specified memory use: two-photon isomerization (TPI) and laser induced surface deformation. Giant birefringence can be generated by TPI and brings about high signal-to-noise ratio (>20 dB) multi-dimensional reversible storage. Polarization-dependent surface deformation arises when increasing the recording energy, which not only facilitates the multi-level storage by black bits (dots), but also enhances the bits' readout signal and storing stability. This facile bits recording method, which enables completely different recording mechanisms in an identical storage medium, paves the way for sustainable big data storage.

Switching to Bright

Switching to Bright

Ultrafast deactivation of bilirubin: dark intermediates and two-photon isomerization.

Bilirubin is a neurotoxic product responsible for neonatal jaundice, which is generally treated by phototherapy. The photoreaction involves ultrafast internal conversion via an elusive intermediate and Z-E isomerization with minor yield (less than 3% in solution). The structure of the intermediate remains unclear. Here, the combination of UV-vis and mid-IR ultrafast transient absorption spectroscopy reports a comprehensive picture of the mechanism and provides essential structural information about the intermediate species. Thus, spectral dynamics during the earliest ps unveils a wavepacket travelling from the Franck-Condon region to the crossing point with a dark state. The latter shows a tighter molecular skeleton than the ground state and decays with 15 ps time constant. Remarkably, the relative contribution of a non-decaying component increases linearly with pump energy, suggesting that Z-E isomerization could also be triggered by two-photon excitation. Implications for the photochemistry of protein-bound open tetrapyrroles are discussed.

Human infrared vision is triggered by two-photon chromophore isomerization.

Vision relies on photoactivation of visual pigments in rod and cone photoreceptor cells of the retina. The human eye structure and the absorption spectra of pigments limit our visual perception of light. Our visual perception is most responsive to stimulating light in the 400- to 720-nm (visible) range. First, we demonstrate by psychophysical experiments that humans can perceive infrared laser emission as visible light. Moreover, we show that mammalian photoreceptors can be directly activated by near infrared light with a sensitivity that paradoxically increases at wavelengths above 900 nm, and display quadratic dependence on laser power, indicating a nonlinear optical process. Biochemical experiments with rhodopsin, cone visual pigments, and a chromophore model compound 11-cis-retinyl-propylamine Schiff base demonstrate the direct isomerization of visual chromophore by a two-photon chromophore isomerization. Indeed, quantum mechanics modeling indicates the feasibility of this mechanism. Together, these findings clearly show that human visual perception of near infrared light occurs by two-photon isomerization of visual pigments.

Synthesis and photophysical properties of a porphyrin-perinaphthothioindigo dye

A new porphyrin-perinaphthothioindigo composite, where porphyrin and perinaphthothioindigo dye are connected though a triple bond, was synthesized. In UV-vis absorption spectra of the composite, absorption originating from the trans-isomer appeared at 655 nm. Upon photoirradiation at > 700 nm, the intensity of this absorption decreased with increase of absorption of the cis-isomer around at 530 nm. The HOMO–LUMO absorption of the cis-isomer is blue-shifted by 125 nm compared to that of trans-isomer due to the lack of π-conjugation. The 2PA cross-section values obtained for both isomers were 2,000 and 700 GM, respectively. The value of 2,000 GM is of the largest class among the values reported for photochromic compounds. The enhancement factors by the connection of porphyrin to perinaphthothioindigo were found to be 3.5–3.9 by measuring cross-section values of bis(TMS-ethynyl)perinaphthothioindigo as the reference compound. Two-photon isomerization of the trans-isomer to the cis-isomer was successfully conducted using femtosecond pulses.

High‐Contrast Photoswitching of Nonlinear Optical Response in Crosslinked Ferroelectric Liquid‐Crystalline Polymers

A conceptually novel materials design, based on crosslinked ferroelectric liquid-crystalline polymers, is demonstrated for efficient switching of a second-order nonlinear optical (NLO) response in the solid state. By controlling the molecular alignment of the NLO moieties through two-photon isomerization of azobenzene molecules, reversible isothermal photocontrol of second-harmonic generation is achieved with contrast of up to 20.

Two-photon assisted poling

I develop a theory that predicts a two-photon-induced molecular polar order in solid polymers at a temperature far below the glass transition temperature of the polymer. Phenomenologically, the rotational mobility of the chromophores is enhanced during a two-photon isomerization process, allowing for polar order to build up in the presence of a dc field that is applied across the solid polymer. No (or negligible) poling is possible in the absence of two-photon isomerization. Using the formalism of Legendre polynomials solves the general equations of the theory, and analytical solutions are derived for the early time evolution and the steady state of this two-photon poling process. The effects of the poling parameters are discussed, and it is shown that the two-photon poling efficiency can be as high as that achieved by dc field poling at elevated temperatures.

基于双光子异构非线性的非相干耦合孤子族

基于双光子异构非线性的非相干耦合孤子族

Gray and dark spatial solitons supported by two-photon isomerization

A theory is presented to show that gray and dark solitons can exist in bulk polymers with two-photon isomerization (TPI) nonlinearity. The soliton FWHM, intensity and phase profiles are discussed in detail. In addition, the stability properties of these TPI solitons are also investigated by employing the stability criterion based on the renormalized momentum.

Ordering of azobenzenes by two-photon isomerization

We report on light induced orientation by two-photon isomerization of azobenzenes in films of polymer. The dynamics of isomerization and orientation by one-photon absorption and two-photon absorption (TPA) are similar, and TPA creates a degree of molecular orientation which is comparable to that achieved by single-photon isomerization, in agreement with the theoretical predictions of two-photon isomeric orientation.

Isomeric orientation by two-photon excitation: a theoretical study

I develop the theory of molecular orientation induced by two-photon isomerization. Phenomenologically, two-photon isomeric orientational hole burning and reorientation induce molecular orientation while rotational diffusion tends to randomize it. Using the formalism of Legendre polynomials solves the general equations of the theory, and analytical solutions are derived for actual physical cases at the early time evolution and the steady state of two-photon excitation. The theory explains the observed results of two-photon molecular orientation, and predicts additional experiments in this direction. The isomerization parameters and the movement of the isomers during polarized two-photon excitation can be quantified by the analytical theory. A theoretical study on the creation of molecular orientation by competing orientational Kerr effect and two-photon orientation is also presented.

Two-photon isomerization and orientation of photoisomers in thin films of polymer

We present experimental evidence of two-photon isomerization and orientation of a diarylethene derivative in films of poly-methyl-methacrylate. The changes of the linear absorption spectrum of the photochromic sample before and after infra-red, high power, pulsed, excitation are consistent with chromophores isomerization induced by two-photon absorption. The slopes of the real-time dynamics of two-photon isomerization showed the square law dependence on the pump light intensity. Two-photon molecular orientation was induced in the polymer samples by polarized infra-red excitation, and it was observed by dichroic absorption on the entire ultraviolet–visible spectrum of the isomers. Molecular reorientation by photoisomerization is inferred as a possible mechanism of the observed two-photon orientation.

Action Spectra of Non-Resonant Two-Photon (NRTP) Isomerization of α,ω-Diphenylpolyenes

Abstract The efficiency of the non-resonant two-photon (NRTP) isomerizations of stilbenes and 1,4-diphenyl-1,3-butadienes were found to depend strongly on the wavelength of the laser pulses. The results not only confirm the 21Ag nature of the excited states responsible for the cis-trans isomerizations but also demonstrate that the action spectra of the NRTP reactions correspond to the two-photon allowed absorption bannds.