91×ÔÅÄÂÛ̳

New Faculty Member and Research on Nanoscale Dynamical Processes: Theory and Computation

Ignacio Franco joined the Chemistry faculty at the 91×ÔÅÄÂÛ̳ in July 2013. Ignacio received his B.Sc. in chemistry from the National University of Colombia in 2001. After completing the diploma program in condensed matter physics at The Abdus Salam International Centre for Theoretical Physics in Trieste in 2002, he moved to the University of Toronto to pursue a Ph.D. in theoretical chemical physics under the guidance of Paul Brumer. Ignacio’s Ph.D. work was in the field of Quantum Control and focused on investigating the use of lasers to induce ultrafast controllable currents along nanoscale junctions. In 2008 he joined Northwestern as a postdoctoral fellow in the groups of Mark A. Ratner and George C. Schatz where he worked on the theory and simulation of single-molecule pulling experiments. He then moved to Berlin to take a position as group leader and Humboldt research fellow in the Theory Department of the Fritz Haber Institute in 2011, where he investigated electronic decoherence processes in molecules.

Research in the Franco lab focuses on theory and computation as applies to dynamical processes occurring at the nanoscale. In particular, the lab uses and develops theoretical techniques that allow the identification of new methods to exert control over the behavior of matter by means of external stimuli, a topic that the group likes to refer to as “Molecules under Stress”. Problems that are currently of interest in the group include: 1. Laser control of electronic properties and dynamics; 2. Electronic decoherence in molecules; 3. Theory and simulation of single-molecule pulling processes; 4. Novel spectroscopies and control in single-molecule junctions.

Selected Publications:

• I. Franco, A. Rubio and P. Brumer. "Long-lived oscillatory incoherent electron dynamics in molecules: trans-polyacetylene oligomers," New J. Phys. 2013, 15, 043004.
• M. MuCullagh, I. Franco, M.A. Ratner and G. C. Schatz. "Defects in DNA: Lessons from Molecular Motor Design," J. Phys. Chem. Lett. 2012, 3, 689-693.
• I. Franco, G.C. Solomon, G.C. Schatz and M.A. Ratner. “Tunneling currents that increase with molecular elongation,” J. Am. Chem. Soc. 2011, 133, 15714-15720
• M. McCullagh, I. Franco, M.A. Ratner and G.C. Schatz. “DNA-based optomechanical molecular motor,” J. Am. Chem. Soc. 2011, 133, 3452-3459
• I. Franco, C.B. George, G.C. Solomon, G.C. Schatz and M.A. Ratner. “Mechanically activated molecular switch through single-molecule pulling,” J. Am. Chem. Soc. 2011, 133, 2242-2249.
• I. Franco, M. Spanner and P. Brumer. “Quantum interferences and their classical limit in laser-driven coherent control scenarios,” Chem. Phys. 2010, 370, 143-150.
• I. Franco, G.C. Schatz and M.A. Ratner. “Single-molecule pulling and the folding of donor-acceptor oligorotaxanes: phenomenology and interpretation,” J. Chem. Phys. 2009, 131, 124902 (2009)
• I. Franco, M. Shapiro and P. Brumer. “Femtosecond dynamics and laser control of charge transport in trans-polyacetylene,” J. Chem. Phys. 2008, 128, 244905.
• I. Franco and P. Brumer. “Minimum requirements for laser-induced symmetry breaking in quantum and classical mechanics,” J. Phys. B 2008, 41, 074003.
• I. Franco, M. Shapiro and P. Brumer. “Robust ultrafast current in molecular wires through Stark shifts,” Phys. Rev. Lett. 2007, 99, 126802.
• I. Franco and P. Brumer. “Laser-induced spatial symmetry breaking in quantum and classical mechanics,” Phys. Rev. Lett. 2006, 97, 040402 (2006).

A summary of the Franco Group research can be found below.

The way that we traditionally use external stimuli is as observational tools that offer insights into the workings of the molecular world. In fact, most of the things we know about molecules we have learned by determining the way that they respond to chemical, electromagnetic or mechanical perturbations. The interest in our group is in exploring, using theoretical tools, an additional facet of the molecular response to external stimuli: its use as an active control tool to manipulate the properties and dynamics of matter in intriguing and potentially useful ways.

We are actively exploring two vastly different limits of the control:

1. Laser control of electronic properties and dynamics in nanoscale systems

and control electronic dynamics in single-molecules, molecular assemblies, interfaces and extended systems. We seek to use tailored laser pulses to create materials that have specific electronic functionalities when driven far from equilibrium. The reason why we want to use lasers over more conventional means (e.g., an applied voltage, or changes in thermodynamic control variables) is that lasers offer the possibility of dynamic manipulation on a ultrafast (femtosecond) timescale.Our interest in this area is to understand how to use lasers to manipulate electronic properties

In order to explore this venue of control, we use theoretical models and numerical simulations of the quantum-classical or fully quantum dynamics of nanoscale systems under the influence of external stimuli as means to identify possible mechanisms for control and to quantify the extent of control that can be achieved.

2. Mechanical manipulation of single-molecule junctions

A particularly rich platform for accessing and directly manipulating the properties of single molecules is molecular junctions, where individual molecules are

sandwiched between two electrodes. Emerging experimental technologies permit the application of forces and voltages simultaneously, allowing for molecular imaging with atomic resolution, control of molecular conformation on a sub-Angstrom scale and probing the ability of molecules to act as a conducting medium as they are mechanically elongated. Our interest in this area is to explore the extent in which the simultaneous application of forces and voltages on single molecules can be used as a powerful avenue for molecular control and as a way to construct novel highly discriminating multidimensional spectroscopies that offer detailed information about molecules in junctions. Such an objective requires extensive theoretical modeling that helps understand and extract information from current single-molecule measurements and guide future experimental developments.

Related links:

• More on Professor Franco