Preparation and Study of 1,8-Di(pyrid-2′-yl)carbazoles

A series of three derivatives of 1,8-di(pyrid-2′-yl)carbazole
were prepared by Stille-type coupling of 2-(tri-n-butylstannyl)pyridine with the appropriate 1,8-dibromocarbazole.
The carbazoles were prepared by appropriate substitution methodologies
on the parent carbazole or by palladium-catalyzed cyclization of di-(p-tolyl)amine to provide the carbazole ring system. An X-ray
structure of the di-tert-butyl derivative confirmed
that both pyridyl groups were oriented for favorable intramolecular
H-bonding to the central N−H. Two orientations of the molecule
were found in the unit cell and this observation was corroborated
by two N−H stretching bands in the solid state IR. Substitution
of N−H by N−D led to increased emission intensity through
diminished intramolecular deactivation of the excited state. The di-tert-butyl derivative formed a tridentate complex with Pd(II),
which showed a red-shifted band attributed to an intraligand charge
transfer state.