PCCP Blog

Japanese scientists have carefully tailored the anion and cation to create of  a new class of ILs which are both strongly hydrophobic and can also hydrogen bond effectively.

The authors found that tetra-n-octylphosphonium paired with ethylphosphonate or n-butylphosphonate were able to form a stable seperate phase after mixing with water while also showing hydrogen bonding characteristics.

This family of ILs could potentially  be used in environmentally friendly separation processes.

Read this exciting PCCP article in full:

Hydrophobic and polar ionic liquids
Yukinobu Fukaya and Hiroyuki Ohno
DOI: 10.1039/C3CP44214D

If you liked this you may also enjoy our recent PCCP themed issue on Interfaces of Ionic Liquids Guest Edited by Professor Frank Endres.

Surface-enhanced Raman spectroscopy (SERS) is a variation of Raman spectroscopy whereby the molecule of interest is first adsorbed onto a surface, often of silver or gold, rather than being studied in solution. The defining advantage of this approach is that the observed intensity of the spectrum is much greater than in solution studies. This effect is strongly associated with the use of nanoscale surfaces for adsorption.

It is clear from reading the article ‘Persistent misconceptions regarding SERS’ by Martin Moskovits, that explaining the mechanism of the phenomenon underlying this technique is still the matter of an intense and interesting debate. It is very possible that this lack of consensus contributes to the fact that SERS is yet to be successfully explained by quantum mechanics, and the theory used to explain it is still classical in nature.

In his article, Moskovits makes it clear that his favoured candidate to explain the enhancement mechanism is the plasmonic theory, which he explains clearly and succinctly. He then systematically examines the other popular theories, and provides arguments that in his view display the superiority of the plasmonic mechanism. He writes particularly strongly against the chemical enhancement theory, and urges its abandonment. Moskovits further suggests that the disagreements amongst SERS researchers may have resulted in opportunities to use the technique being missed due to uncertainty over its mechanism.

As research techniques undergo simultaneous development by multiple research groups, it is unsurprising that differences of opinion and opposing theories arise. If a particular view becomes popular, it can become so widely accepted that it is taken as fact and remains unchallenged for many years. It is therefore important that opposing views are presented, as in this article, in order that the relevant research community may consider their merits.

by Victoria Wilton

Form your own opinion – read the Perspective today:

Persistent misconceptions regarding SERS
Martin Moskovits
DOI: 10.1039/C2CP44030J

Ionic liquids are the new black; a nonsense statement, but very true. Recyclable ionic liquids are the new solvents of choice as they allow for extensive recycling, novel processes and treatments and higher durability of devices. Ionic liquids are also just new, with unexplored physical and chemical properties. In a recent PCCP paper Torriero and co-workers target the issue of referencing electrochemical measurements in ionic liquids.
Four classical metallocene redox couples are investigated in this paper. Ferrocene/ferrocenium is the reference redox couple of choice, but has been shown to be sensitive so specific solvation and ion pairing. This is also the case for ionic liquids, just much more extreme. In the four studied ionic liquids the variation is a full 100 mV. A similar large variation is found for cobaltocenium/cobaltocene. This variation presents a major issue if either of these redox couples are used as an internal reference in electrochemical experiments.
The per-methylated derivatives sandwich complexes, derived from 1,2,3,4,5-pentamethyl-cyclopentadienyl or Cp* (Cp-star), vary, but vary less. The relative change, measured as the difference in reduction potential of between Cp*₂Fe and Cp*₂Co⁺, is only a few millivolts. The result presented in this paper shows that the Cp* sandwich complexes may show promise as the new standard in electrochemical experiments in ionic liquids.

The limitation of the suggested internal references are discussed in full in:

Assessment of permethylated transition-metal sandwich complexes as internal reference redox systems in ionic liquids
Angel A. J. Torriero, Jaka Sunarso, Maria Forsyth and Cristina Pozo-Gonzalo
Phys. Chem. Chem. Phys., 2013, 15, 2547-2553
DOI: 10.1039/C2CP43177G

by Dr Thomas Just Sørensen

The commercial ATTO 465 dye, based on 9-alkylated proflavine, appears ever so simple: a 2,7-diamino-9-alkyl-acridinium fluorophore with a relatively remote carboxylate group. Even so Arden-Jacob and co-workers find that the photophysical behaviour is far from straightforward. This despite the fact that the cousin: ATTO 495 with the 2,7-bis(dialkylamino)-9-alkyl-acridinium dye, is perfectly simple.

ATTO 465 is interesting. As dye it is not spectacular: it absorbs light at roughly a fifth of the best possible and emits around half of the number of photons it absorbs. Nothing unusual here, but the shape of the spectra, the way the dye changes depending on which solvent that surround it, and mechanisms it uses to dissipate energy; that is unusual. And apparently the explanation lies with the hydrogen atoms on the peripheral amino groups?

A dye can be reduced to a group of electrons moving in a box of nanometer dimensions: a small antenna. The macroscopic counter-piece is a radio antenna, which contains a number of electrons that move in the volume of the antenna. If the dye is changes, the interaction between the nano-antenna and light changes. It can be a variation in colour or a difference in the amount of light emitted. ATTO 465 is a box where both the shape and the number of electrons can change. By bonding hydrogen to the amino groups electrons are removed, the bonding also twists the amino groups resulting in a differently shaped box. Unfortunately the ‘twisting’ is not discreet and many different shapes will be present at all times, as long as there are protons (hydrogen atoms) in the solution that surrounds ATTO 465. The result is the complex photophysical behaviour observed and discussed by Arden-Jacob and co-workers.

Much more detail can be found in the full PCCP article:

Ultrafast photoinduced dynamics of the 3,6-diaminoacridinium derivative ATTO 465 in solution
Jutta Arden-Jacob, Karl-Heinz Drexhage, Sergey I. Druzhinin, Maria Ekimova, Oliver Flender, Thomas Lenzer, Kawon Oum and Mirko Scholz
DOI: 10.1039/C2CP43493H

by Dr Thomas Just Sørensen

Chiral structures interact with circularly polarised light. Gennaro Pescitelli and co-workers have investigated the effects of the close contact between handed molecules in micro-crystals in their interaction with light. The well-rounded study explains—as promised–the specific case, but does it take us closer to a general structure-property relationship regarding the preferential absorption of one handedness of light? And is such as a correlation even possible?

In ”Intermolecular exciton coupling and vibronic effects in solid-state circular dichroism: a case study” by Gennaro Pescitelli, Daniele Padula and Fabrizio Santoro, the finer details of the interaction between circularly polarised light and chiral matter is discussed. In this specific case, homochiral microcrystals are investigated experimentally and theoretically. The results presented are impressive, as the theoretical model fits and explains the experimental observation, but why is this study so important? What is this chirality? And which answers are we looking for?

Chirality and the word chiral derive from the Greek word cheir or hand: chiral can be read as handed and chirality as handedness. The definition of a chiral object is that it cannot be superimposed on its mirror image, just as our hands. Chirality is hugely important as every biological building block that makes up our hands, and indeed the rest of us, is handed. It comes in a left-hand and a right-hand form.

As it is the entire biological machinery on earth is almost exclusively left-handed. How this came about, we do not know, but it is suggested that we, in our part of space, have an abundance of circularly polarised light emitters of a certain handedness, and that this has caused the handedness of our biology. Chirality and circularly polarised light are linked. Each can be described of having a specific handedness and one handedness of light interacts with one handedness of chiral matter. An abundance of right-handed light in our part of the universe may have induced the single handedness of our biology.

In order to figure out how the homo-chirality of the biosphere on earth arose, we need to understand how circularly polarised light and chiral material interacts; exactly what Gennaro Pescitelli and co-workers are investigating. Studies like this, where experiment and highly advanced theory is used to correlate observations and the chiral structure of the material, are needed if we are to understand how chirality in a molecular framework absorbs one specific handedness of light.

We understand how regular material (not handed) and normal light (linearly polarised) interact, and how to design materials that interact with light in a desired fashion. We cannot yet design materials that absorb a specific handedness of light. The paper  ”Intermolecular exciton coupling and vibronic effects in solid-state circular dichroism: a case study” by Gennaro Pescitelli, Daniele Padula and Fabrizio Santoro takes us one step closer, it was published in of Physical Chemistry Chemical Physics 2013, 15, 795-802.

by Dr Thomas Just Sørensen

Read this fascinating study today:

Intermolecular exciton coupling and vibronic effects in solid-state circular dichroism: a case study
Gennaro Pescitelli, Daniele Padula and Fabrizio Santoro
DOI: 10.1039/C2CP43660D