How an Eight-Membered Ring Alters the Rhodamine Chromophore

Readily
available phenylene-1,3-diamines can be converted into
unprecedented analogues of rhodamine and malachite green possessing
a central eight-membered ring in three steps. The overall process
couples a cyanine chromophore with a urea bridge giving rise to new
dyes possessing distinct spectral characteristics: absorption of orange
light combined with a weak emission of red light both in solution
and in the crystalline state. Their photophysics is governed by the
twist of lateral phenyl rings and intramolecular and intermolecular
CT transitions.