Grafting Spiropyran Molecular Switches on TiO₂: A First-Principles Study

Abstract

To explore the optoelectronic properties of spiropyran molecular switches adsorbed onto TiO 2 anatase surfaces, we performed a density functional theory (DFT)/timedependent density functional theory (TD-DFT) study considering the two isomeric forms of the photochromes anchored by both their sides. A comparison between the features of the hybrid and isolated systems is proposed to probe the adsorption effects on both subsystems. This comparison considered, on the one hand, the density of states and the alignment of the energy levels, and, on the other hand, the UV−visible spectra of these systems. We show that several electronic and optical characteristics of the hybrid systems are modulated by the open/closed state of the photochromes. These properties are also modified by the localization of the anchor group on the photochrome.

How organic switches grafting on TiO2 modifies the surface potentials: theoretical insights

“…8 are 3.02, 2.74 and 3.39 eV for the (100), (101)-I and (101)-II unbound TiO 2 surfaces, respectively. Our computed first absorption band of the (101)-I unbound surface is consistent with other theoretical calculations (2.56 eV) 34 but is underestimated compared with the experimental measurements, which is located between 3.4 and 4.9 eV performed on TiO 2 films with different thicknesses. 64 To obtain the exact optical properties in the UV-vis range, the scissors operation 65 of 0.66 eV, which corresponds to the difference between the experimental measurement of the thinnest TiO 2 films (∼15 nm) considered in a previous study and our theoretical result, was carried out in an optical absorbance of the hybrid system.…”

“…The perpendicular conguration was also demonstrated to be the optimal adsorption mode in terms of energetic and dynamical stability. 30,[47][48][49][50] The effectiveness of adding anchor groups was predicted through both experimental and theoretical studies, 34,47,49 while the covalent bonding of trimethoxysilane refers to a graing reaction with silanes in the real synthesis process. 50,51 To consider the effect of the oxidization of PFOS due to UV illumination, one of the uorine atoms at the end of the carbon chain of pristine PFOS (labeled as PFOS-F) was replaced by a hydroxyl group, which was labeled as PFOS-OH.…”

“…19,31,32 In this case, a good understanding of hybrid systems is crucial to quantify the interplay between the organic switches and inorganic substrates during the photochemical process. To explore the optoelectronic properties of these hybrid systems, numerous studies have carried out, including density functional theory (DFT)/time-dependent density functional theory (TDDFT) investigation of a series of photochromic derivatives of trans/cis-AZB, 33 open/closed-SP 34 and open/closed-DTE 33,35 adsorbed onto anatase and rutile slabs. To explain the switchable wettability of TiO 2 nanoparticles modied with trimethoxysilane under UV illumination, a series of experiments was carried out to conrm the oxidization process for the degradation of trimethoxysilane.…”

“Redox switches” of Fe species on zeolite catalysts: Modulating the acidity and the para-xylene yield from methanol

“…Molecular switches are molecules in which bonds, electronic state, or structure change in response to environmental stimuli such as light, heat, electrical field, pH, atmosphere, or pressure; they are widely used in photonics, bioscience, chiral synthesis, and computer science for logical calculations [1][2][3][4][5][6][7][8] . Although molecular switches have been widely employed in solutions and polymer systems, their use in heterogeneous catalysis to modulate the properties and performance of the catalyst has been rarely reported.…”

Light, Force, and Heat: A Multi-Stimuli Composite that Reveals its Violent Past

“…Self-reporting materials are capable of showing a measurable, often visible indication of the conditions they have been subjected to. Spiropyrans are molecular switches that undergo a reversible molecular transformation to a merocyanine (MC) form in response to different stimuli such as mechanical stress, − light, and heat and thereby showing a color change. , As the intensity of the color is linked to the amount of active molecules present, spiropyran should be an ideal self-reporting material. , Several self-assembly, self-reporting materials and optical sensors based on spiropyran have been successfully produced. − In most of such systems, the spiropyran is either covalently linked to a polymer chain, − or grafted on metallic surfaces. − Most known systems of spiropyran as a mechanical stress indicator require its covalent incorporation into the main chain or as cross-links of the polymer. − This results in long synthesis routes from commercially available starting materials to the final product, thus complicating the scale-up process. , There have been examples of studies on the mechanical sensitivity of spiropyran derivatives in crystal form, illustrating mechanochromic switching under high hydro static pressure. − This implies that spiropyran can be used as an additive in the polymer composite system and would provide a more cost-effective solution. − Photoinduced mechanical switching of spiropyran in a composite system has been demonstrated in poly­(ethyl methacrylate- co -methyl acrylate) (PEMMA) films . These films were produced by blending 3 wt % of spiropyran, and the stiffness of the material was altered by the photoinduced switching.…”