Photoisomerization Dynamics in Photochromic Molecules
A trend
known as Moore’s first
law states that, by shrinking their size, the number of transistors on
computer chips will double every 18 months. These advances however come at
the expense of exponential increase in cost for new chip-fabrication plants
(Moore’s second
law). Molecular scale electronics (MSE) has the potential to go much
smaller. Most importantly, as molecular electronics relies on self-assembly
rather than lithography it can beat Moore’s second
law. Consequently, the molecular way of thinking will become increasingly
profitable as the size of electronic devices continues to shrink.
Photochromic
molecules undergo reversible structural changes upon light-activation and
thus show a potential for use as building blocks in active molecular scale
devices. Fundamental requirements for application of photochromatic system
to photonic devices include high efficiency, fast response to an external
stimulus, and a long lifetime. While many molecules can offer ultrafast
response times, multiple relaxation pathways can lead to inefficient
switching or photochemical reactions resulting in destruction of the
molecular device. As the quantum yield of the desired outcome is governed
by the competition between different pathways only by speeding up the
desired process (e.g. ultrafast switching) it can beat out all dissipative
processes. The rational design of active molecular devices thus requires a
thorough understanding of electronic relaxation dynamics of its building
blocks. We use time-resolved photoelectron spectroscopy combined with
optical and chemical techniques to characterize and ultimately control
photoisomerization dynamics in photochromic molecules.
