The first electronic absorption bands of the title compounds can all be assigned to the intramolecular charge-transfer transitions. The solvent effects on these bands are quite analogous to those on the absorption bands characteristic of binary charge-transfer complexes. Especially, when the title compounds are dissolved in trifluoroacetic acid, marked bathochromic shifts of the first bands are observed, in harmony with their charge-transfer character. Such solvatochromism is obviously due to the hydrogen-bond formation between the solute and the solvent molecules. When strong hydrogen bonding occurs, the electron affinity of the 2-methylene-1,3-indandione moiety increases by about 0.41 eV.

The Electronic Spectra of Intramolecular Charge-transfer Compounds and Their Marked Solvatochromism in a Strong Hydrogen-bonding Solvent: 2-(Arylmethylene)-1,3-indandiones and 2-(1-Naphthyl)-p-benzoquinone

For analogous normal vibrations in conjugated systems of a similar type a linear relationship often exists between vibrational frequencies and bond orders. We find that this linearity can, in principle, be extended to include conjugated systems in both excited electronic states and ionic states. This indicates that the linearity covers a full range of bond order conceivable for conjugated systems. Such an aspect of molecular vibrations gives a concise and sometimes decisive clue not only to vibrational assignments but also to structural analyses of conjugated systems in various electronic states. Symmetric C=C stretching vibrations of ethylene and tetracyanoethylene nicely illustrate this situation.

Full-range bond-order dependence of intramolecular vibrations: Ethylene and tetracyanoethylene.

: Five aromatic hydrocarbon-tetracyanoethylene (TCNE) complexes were dispersed in sodium chloride pellets and subjected to high pressures (0-25 kbar). The charge transfer absorption was enhanced and displaced toward lower energies at the highest pressure. An exception is the crystalline complex HMB-TCNE which exhibits a blue shift at the highest pressure. The doublet structure in both charge transfer bands of naphthalene-TCNE can be observed at 1 atm and at at higher pressures. The importance of the relative sizes of donor and acceptor in environmental interactions are discussed. (Author)

A. H. Kadhim

Papers

Spectroscopy of eda complexes at high pressures. v. absorption of crystalline tcne complexes.