Negative Solvatochromism in a N-Linked p-Pyridiniumcalix[4]arene Derivative.

In this paper, we report the synthesis, structural characterization, and solvatochromic properties of a N-linked p-pyridiniumcalix[4]arenediol derivative 1. In the solid state, 1 forms a dimeric assembly stabilized by a network of weak H-bonding interactions involving acetonitrile solvent molecules. In solution, 1 shows a peculiar negative solvatochromism which was rationalized with the aid of TD-DFT calculations. The species responsible for this phenomenon is the monodeprotonated betainic form of 1 which is easily formed at pH close to neutrality.