Localized molecular excitons in polyaniline

Doping of polyaniline with 6-cyano-2-naphthol

The conductivity of polyaniline (PANI) is ascribed to its emeraldine salt (PANI-ES), which is formed by protonation of its emeraldine base (PANI-EB) by acids. Generally, mineral acids are used for this purpose, but the use of dopants and additives to maintain the required acidity provides an alternative method to the preparation of PANI-ES. The present work attempts to achieve the protonation by the use of a weak organic acid, namely, 6-cyano-2-naphthol (6CN2), which is generally used as a superphotoacid, as its excited state pKa is significantly smaller than its ground state pKa. The question here is if the protonation of the aniline moieties in PANI takes place and if it does, whether it takes place by dissociation of the ground state or the excited state of 6CN2. Room temperature conductance measurements were carried out to see the effect of doping. The formation of PANI-ES from PANI-EB has been monitored by UV-vis spectrophotometry. When a polar counterion is inserted into the polymer matrix, it changes the environment of the nearby chains by introducing defects, reorganization of charges as a result of interaction with the polymer. Morphological investigation was done using optical microscopy, field emission gun scanning electron microscopy (FEGSEM), and field emission gun transmission electron microscopy FEGTEM. The influence of 6CN2 on the crystallinity of the polymer was determined by X-ray diffraction (XRD).

Polyaniline: an Old Polymer with New Physics

Polyanilines have been known for over one hundred years. Recent studies of this chemically flexible polymer have demonstrated unusual electronic phenomena in both the insulating forms and the conducting forms. Studies of both forms show that the origins of the electronic phenomena are substantially different than those observed in polyacetylene and related earlier studied conjugated carbon backbone polymers. Unusual aspects include the formation of massive polarons upon photoexcitation in the insulating forms. These polarons have unusual time dynamics associated with the roles of ring-flipping and ring-conformation in the polymer system. A new model for the effects of electron lattice coupling via ring rotation has been introduced. The “metallic” form of the polymer shows that the metallic state is associated with the ordered regions of the doped polymer. The roles of localization are important in leading to the formation of a textured, granular metal. At low temperatures for emeraldine salt, and at higher temperatures for derivatized polyanilines, localization is important. Potential new technologies based on the polyanilines, including optical information storage, controlled microwave absorption, and use of a self-protonating derivative that is soluble in aqueous media are noted.

Structures and dynamics of molecules on liquid beam surfaces

In this review, we describe experimental studies on structures and dynamics of molecules on clean liquid surfaces in a vacuum. These studies use clean-surface preparations in combination with highly sensitive laser-, photoelectron-, and mass-spectroscopic techniques. In particular, we refer to our recent studies on solvation structures and reactions on various solution surfaces using liquid beam-multiphoton ionization-mass spectrometry. These include (a) aggregation of solute molecules on solution surfaces such as formation of solute pairs, clusters, and islands; and (b) chemical reactions induced by photoexcitation and -ionization, such as a nucleophilic reaction of phenyl ketones, polymerization of halo-anilines, and reduction of cations by solvated electrons.