Optically induced angular motion of single-molecules

Chemical Physics Letters, 1996

Molecular dynamics calculations and optical spectroscopy measurements of weakly active infrared modes are reported. The results are qualitatively understood in terms of the “motional diminishing” of IR lines, a process analogous to the motional narrowing of a nuclear magnetic resonance (NMR) signal. In molecular solids or liquids where the appropriate intramolecular resonances are observable, motional diminishing can be used to study the fluctuations of the intermolecular interactions having time scales of 1 to 100 ps.

Pure and Applied Chemistry, 2000

The following article is a tribute to the late Almeria Natansohn and is based on a brief summary of her research in azopolymers. She showed that reversible trans–cis–trans photoisomerization of aromatic azo groups covalently bonded within polymers could trigger a variety of motions in the polymer materials at molecular, nanometer, and micrometer levels. The photoinduced motions could be limited only to the azo rigid chromophore or could involve many polymer chains and ordered domains. Some of the effects of these motions such as reversible photo-orientation of chromophores, amplification effects, photorefractive effects, formation of surface relief gratings (SRGs), and photoinduced chirality and switching in amorphous and liquid-crystalline (LC) polymer films are discussed in relation to the polymer structure and physical parameters. Possible photonic applications originating from these phenomena are also mentioned.

Macromolecular Chemistry and Physics, 2007

Physical Chemistry Chemical Physics, 2009

The combination of a photochemical and a thermal equilibrium in overcrowded alkenes, which is the basis for unidirectional rotation of light-driven molecular rotary motors, is analysed in relation to the actual average rotation rates of such structures. Experimental parameters such as temperature, concentration and irradiation intensity could be related directly to the effective rates of rotation that are achieved in solution by means of photochemical and thermal reaction rate theory. It is found that molecular properties, including absorption characteristics and photochemical quantum yields, are of less importance to the overall rate of rotation than the experimental parameters. This analysis holds considerable implications in the design of experimental conditions for functional molecular systems that will rely on high rates of rotation, and shows that average rotation rates comparable to ATPase or flagella motors are within reach assuming common experimental parameters.

Chemphyschem : a European journal of chemical physics and physical chemistry, 2015

We study the photoisomerization of azobenzene chromophores embedded into a polymer matrix by using coarse-grained simulations. Two types of beads are considered: t- and c-beads, which are rich in trans and cis isomers, respectively. Simulations combine deterministic (molecular dynamics) and stochastic (random-type switching) parts. The ratio between the characteristic times for photoinduced reorientation and for orientation relaxation is tuned to be of the order found in experiments. The essential features of the phenomenon: 1) the existence of a stationary state, and 2) anisotropic distribution of the orientations of t-beads (orientation hole-burning effect), are reproduced. We study population dynamics of c-beads and the strength of the orientation hole burning, depending on the illumination wavelength and its intensity. The form of the reorientation potential of the mean force acting on the t-beads is analyzed and its use is validated.

The Journal of Physical Chemistry Letters, 2013

The Journal of Physical Chemistry A, 2010

We report on the rotational diffusion dynamics of two different chromophores, resorufin and 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoic acid (NBDHA) in water and N-octyl-2-pyrrolidone (NOP) solvents. We measure the induced orientational anisotropy function, R(t), using time-correlated single photon counting. Our data show that both chromophores exhibit single exponential anisotropy decays in aqueous solution and two-component exponential anisotropy decays in NOP. The change of the anisotropy decay functionality indicates that the effective rotor shape swept out by solute rotational motion is different in the two solvents. We interpret these findings in the context of Chuang and Eisenthal's theory of fluorescence depolarization by rotational diffusion. The similarity in the behavior of the two different chromophores in these solvent systems points to solvent-solvent interactions and local organization as the dominant factors in mediating motional dynamics.

Canadian Journal of Chemistry, 1998

Molecular Crystals and Liquid Crystals, 2005

Photoinduced Anisotropy and All-Optical Poling are the result of two mechanisms, the angularly selective excitation of molecules (Angular Hole Burning) and the rotation of molecules during the excitation-relaxation cycle (Angular redistribution). In this paper we recall some previous results and we present two new experiments. The first one demonstrates the prime importance of reversible photoisomerization for angular redistribution: we compare dichroism and second harmonic generation, with photoisomerizable molecules and non photoisomerizable ones. The second experiment shows an example of the behavior of photoinduced anisotropy, in a liquid crystal azo-polymers: a 3D characterization of anisotropy is necessary.