Single molecule multilevel switch or digitized neuron

Single molecule multi-level switch can reversibly switch between multiple conducting states. If possible conducting states are five, including the ground or the neutral state, then these levels are denoted as 0, 1, 2, 3, 4.

In the concept of binary switches we have only 2 states, 0 and 1. To create an adaptable hardware we need multilevel switches. We are working and continuously publishing multilevel switches using organic molecules since 2004.

However, there is a paradigm shift in the last couple of years since we are not looking for multilevel aspects into the bulk, rather into the system within a few atomic diameter area.

Note that, we define neuron as a device that can switch between multiple states reversibly and communicate more than one at a time.

Vertical Parallel Processor

In the early periods of 2005, we were working on supramolecular electronics in a planer surface and trying to explore the possibility of remote sensing processing. From this project we learnt two very important lessons for building a bio-processor.

First, vertical measurement always decreases noise compared to horizontal transport measurement. Second, external environment can always trigger information processing of the hardware without physical contact.

We constructed smallest prototype of such processor, and filed a patent too, however, later we realised that planar arrangement does not allow maximum data acquisition per unit time.

Therefore, we have made a major design change and at this moment we are designing VPP using an spherical architecture.

See Movie: Working mechanism of vertical parallel processor

Supramolecular electronics

Definition of supramolecular electronics is that if a supramolecular device C is produced using two components A and B, then C should demonstrate property of A and property of B. Side by side some new properties would be generated from the structural peculiarities. We explore enormous possibilities thus found in the framework of architectures built by weak interaction.

One example of such work is tuning of leakage or noise current in a supramolecular assembly. We used three different polymers to tune leakage current through the assembly of one particular molecular switch.

Currently we have made a major paradigm shift from this direction. We are designing and building up ordered spherical assemblies doped with multilevel molecular switches or neurons.

Molecular memory-switch Cluster

At the very begining of our study we explored global switching behavior of a large number of molecules say couple of billions. The switching behavior of such a large number of molecules offered very interesting display of physical interactions when we studied the same using impedance spectroscopy.

This has been an amazing experience for us to see that how randomly distributed particular molecules give rise to particular circuits in a large molecular assembly.

There is no doubt circuiting power of nature is enormous.

Organic Solar Cell

Till now, we have worked on two different kinds of organic solar cells. First, donor acceptor based organic solar cell, and second, solid state dye sensitised solar cell.

Donor acceptor type solar cells are very easy to make. Take donor and acceptor molecules and mix them in such a way that the exciton generated at their junction is transported without dissipation. Just opposite hardware requirement to an organic light emitting diode.

But try to do this, then only you can realise the problem. Just imagine, after creation of exciton you need to pass it through a path where there is no junction. At the same time, remember you need many many excitons for better performance. Anyway, we tried to solve this problem, using supramolecular assembly.

In case of DSSC, we have used Calf-thymus DNA and Adenine base as an alternative to liquid electrolyte. Our sensitizing dye was Rose Bengal.

Plastic Memory

At the very begining of our research, we planted bits in the non-conjugated or day-to-day plastics. A switchover of material from plastic to single molecule led us to build switching devices that could replace the field effect transistor based switching devices.

Plastic memory was important because it is simplest and cheapest way to store bits.

Contact: Anirban Bandyopadhyay, National Institute for Materials Science, Tsukuba, Japan-305-0037