DOI: 10.1002/asia.200900254 Reversible Mechanical Induction of Optical Activity in Solutions of Soft- Matter Nanophases Oriol Arteaga, [b] Carlos Escudero, [a] Gerard Oncins, [c] Zoubir El-Hachemi, [e] Joan Llorens, [d] Joaquim Crusats, [a] Adolf Canillas, [b] and Josep M. Ribó* [a] Introduction The formation of chiral-shaped inorganic nanophases by an initial induction with chiral organic compounds is being studied in the formation of inorganic biological structures (e.g., micro-shells). [1] This constitutes, in fact, the basis of a new emerging field aimed at the biomimetic preparation of novel chiral nanostructures and materials starting from achi- ral materials. [2] The action of the mechanical forces originated by flows on chemical phenomena are generally considered to be un- detectable and not significant, in spite of their accepted im- portant role in some topics, for example, protein folding. [3] However, the role of chiral flows (stirring vortices) in the ir- reversible induction of chirality during the self-assembly of achiral building blocks has been previously reported. [4] These scarce previous experimental results correspond to aggregates of the diprotonated 5-phenyl-10,15,20-tris(4-sul- fonatophenyl)porphyrin (H 2 TPPS 3 ; Scheme 1) obtained in a stirring vortex, [4a–d] dendrimer aggregates obtained by spin- coating, [4e] and the aggregates of diprotonated meso-tetra- phenylporphyrin obtained in a centrifugal liquid membrane cell. [4f] Nevertheless, these reports have not led to the devel- opment of new chiral methodologies. All these previous re- ports describe experimental systems containing the porphy- rin chromophore, as it seems to be an ideal chromophore probe for the detection of chirality by CD spectroscopy be- cause of its high oscillator strength and degenerate transi- tions. [5] The difficulty in these types of studies is to ascertain whether or not the experimental optical polarization corre- sponds to CD [or circular birefringence (CB)] or to other anisotropies of the sample, that is, linear dichroism (LD) and linear birefringence (LB) contributions. [6] In the case of particles in solution, the measurement of the optical polari- zation properties has the additional difficulty that the natu- ral convection flows may lead to an average orientation of Abstract: Nanophases of J-aggregates of several achiral amphiphilic porphyr- ins, which have thin long acicular shapes (nanoribbons), show the imme- diate and reversible formation of a sta- tionary mechano-chiral state in the so- lution by vortex stirring, as detected by their circular dichroic signals measured by 2-modulator generallized ellipsome- try. The results suggest that when a macroscopic chiral force creates supra- molecular chirality, it also creates an enantiomeric excess of screw distor- tions, which may be detected by their excitonic absorption. An explanation on the effect of the shear flow gradi- ents is proposed on the basis of the ori- entation of the rotating particles in the vortex and the size, shape, and me- chanical properties of the nanoparti- cles. Keywords: chirality · circular dichroism · nanoparticles · self- assembly · supramolecular chemis- try [a] Dr. C. Escudero, Dr. J. Crusats, Prof. J.M. Ribó Department of Organic Chemistry and Institute of Cosmos Science (ICC), University of Barcelona Martí i Franqus 1, 08028-Barcelona, Catalonia (Spain) Fax: (+ 34) 934021251 E-mail: jmribo@ub.edu [b] O. Arteaga, Dr. A. Canillas Department of Applied Physics and Optics Science, and Institut de Nanocincia i Nanotecnologia (IN 2 UB), University of Barcelona Martí i Franqus 1, 08028-Barcelona, Catalonia (Spain) [c] Dr. G. Oncins Scientific Services and Institute for Bioengineering of Catalonia (IBEC), University of Barcelona Martí i Franqus 1, 08028-Barcelona, Catalonia (Spain) [d] Dr. J. Llorens Department of Chemical Engineering University of Barcelona Martí i Franqus 1, 08028-Barcelona, Catalonia (Spain) [e] Dr. Z. El-Hachemi Centro de Astrobiología CSIC-INTA Ctra. Ajalvir Km. 4, 28850-Torrejón de Ardoz, Madrid (Spain) Chem. Asian J. 2009, 4, 1687 – 1696 # 2009 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 1687