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Surface relief gratings in azo-polymers revisited
摘要： We use the concept of vectorial photochemical tweezing to rationalize the experimental observations of surface relief gratings in azo-polymers, e.g., the photochemically induced motion of the polymer in a one-dimensional intensity gradient produced by two-laser beam interference. Vectorial motion of matter occurs when photochemically active, polarization sensitive molecules are photo-selected in a gradient of light intensity. Directional motion is imposed parallel to the gradient vector with an efficiency that depends on the respective orientations of the vectors of light polarization and intensity gradient. Different combinations of polarizations of the interfering beams leading to differing efficiencies of matter motion are revisited and discussed. We show that the magnitude of photoisomerization force dictates the efficiency of the observed matter motion. We also show that the spatial distribution of the photo-moved matter is Gaussian, the height and width of which exhibit an intensity dependence which is predicted by the theory of photochemical vectorial tweezing; both theory and experiments indicate that the photoisomerization force, which acts on thin films of azo-polymers, is in the mN range.
关键词： photoisomerization force,vectorial motion,photochemical tweezing,azo-polymers,surface relief gratings
更新于2025-09-09 09:28:46
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Experimental and first principles investigations on the photoisomerization and electrochemical properties of chlorophosphonazo III
摘要： Photoresponsive molecules have been widely applied to solar cells and molecular devices. In this manuscript, we report the photoresponsive behaviours of chlorophosphonazo III, a cheap commercially available molecule and previously only used as a colorimetric reagent for earth metals, focusing on the photoisomerization properties in solution or on TiO2 substrates. Apart from the optomechanical properties, the chlorophosphonazo dye is found to generate a weak but non-negligible photocurrent under the visible light in aqueous environment. Density functional theory calculations are used to understand the structural, electronic and optical properties of the functional molecule. Possible routes to enhance the optoelectronic and optomechanical performance of chlorophosphonazo III toward multiple functions in integrated devices where both of the optomechanical and optoelectronic performances are desired are suggested.
关键词： Anchoring Group,Photocurrent,Photoisomerization
更新于2025-09-09 09:28:46
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[Topics in Current Chemistry Collections] Multidimensional Time-Resolved Spectroscopy || Multidimensional Vibrational Coherence Spectroscopy
摘要： Multidimensional vibrational coherence spectroscopy has been part of laser spec-troscopy since the 1990s and its role in several areas of science has continuously been increasing. In this contribution, after introducing the principals of vibrational coherence spectroscopy (VCS), we review the three most widespread experimen-tal methods for multidimensional VCS (multi-VCS), namely femtosecond stimu-lated Raman spectroscopy, pump-impulsive vibrational spectroscopy, and pump-degenerate four wave-mixing. Focus is given to the generation and typical analysis of the respective signals in the time and spectral domains. Critical aspects of all multidimensional techniques are the challenges in the data interpretation due to the existence of several possible contributions to the observed signals or to opti-cal interferences and how to overcome the corresponding difficulties by exploiting experimental parameters including higher-order nonlinear effects. We overview how multidimensional vibrational coherence spectroscopy can assist a chemist in under-standing how molecular structural changes and eventually photochemical reactions take place. In order to illustrate the application of the techniques described in this chapter, two molecular systems are discussed in more detail in regard to the vibra-tional dynamics in the electronic excited states: (1) carotenoids as a non-reactive system and (2) stilbene derivatives as a reactive system.
关键词： Excited states,Photoisomerization,Multidimensional spectroscopy,Coherence spectroscopy,Vibronic coupling,Ultrafast laser spectroscopy,Raman,Vibrational spectroscopy
更新于2025-09-04 15:30:14
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Dynamically evolving surface patterns through light-triggered wrinkling erasure
摘要： For many applications, it is an imperative that changes in polymer surface topography, especially periodic patterns, can be triggered on command by a well-defined remote signal. In this contribution, we report a light-induced cascade of changes in wrinkling wavelengths on thin polymer layers supported by an elastomeric substrate under tensile stress. Through the applied supramolecular design, the effect of varying the ratio of light active and light passive components can be easily assessed, and it is shown that both the cascade type as well as the rate of the progress of the dynamic light-induced changes can be tuned by this ratio, as well as by the light intensity. Furthermore, for the reported phenomena to occur, nominally only every 20th polymer repeat unit needs to be occupied by a chromophore, which makes the conversion of the sub-nm photoisomerization reaction into 10 μm - scale changes of periodic surface patterns extremely efficient.
关键词： light-triggered wrinkling erasure,polymer surface topography,photoisomerization,supramolecular design,elastomeric substrate
更新于2025-09-04 15:30:14
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Ultrafast Dynamics of Encapsulated Molecules Reveals New Insight on the Photoisomerization Mechanism for Azobenzenes
摘要： Spatial con?nement can have a profound impact on the dynamics of chemical reactions, especially for isomerization reactions that involve large amplitude structural rearrangement of a molecule. This work uses ultrafast spectroscopy to probe the e?ects of con?nement on trans→cis photoisomerization following ππ? excitation of 4-propyl stilbene and 4-propyl azobenzene encapsulated in a supramolecular host-guest complex. Transient absorption spectroscopy of the encapsulated azobenzene derivative reveals the formation of two distinct excited-state species with spectral signatures resembling the cis and trans isomers. Formation of the cis species indicates a direct excited-state isomerization channel that is not observed in cyclohexane solution. Comparison with the stilbene analogue suggests that this “hot” excited-state isomerization pathway for encapsulated azobenzene involves primarily in-plane inversion, whereas a ten-fold increase of the excited-state lifetime for the trans isomer suggests that crowding in the capsule hinders isomerization from the relaxed S1 geometry of the trans isomer. This work provides new mechanistic insight on the relative roles of inversion and rotation in the ultrafast photoisomerization of azobenzene derivatives.
关键词： Azobenzenes,Encapsulated molecules,Supramolecular host-guest complex,Photoisomerization,Ultrafast dynamics
更新于2025-09-04 15:30:14
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A Highly Fluorescent and Photoresponsive Polymer Gel Consisting of Poly(acrylic acid) and Supramolecular Cyanostilbene Crosslinkers
摘要： A poly(acrylic acid)-based polymer gel exhibiting strong fluorescence and high photoresponsibility is prepared by using a cyanostilbene derivative as a self-assembling supramolecular crosslinking agent, which generates conceptually new multiple hydrogen bonds in the gel system. This polymer gel in ethanol shows the gel-to-sol transition upon UV light irradiation with concomitant fluorescence color and intensity changes, which are attributed to the trans-to-cis photoisomerization of the supramolecular crosslinkers. Aggregation-induced enhanced emission (AIEE) behavior of the trans-cyanostilbene derivative enables a highly fluorescent polymer gel (ΦF = 0.68) with green color (λem = 541 nm), which can be switched into a blue fluorescent sol (λem = 506 nm and ΦF = 0.12) upon UV irradiation.
关键词： polymer gels,fluorescence switching,photoisomerization,gel-to-sol transition,hydrogen bonding
更新于2025-09-04 15:30:14