Using a rigid xanthene scaffold, a series of boradiazaindacene derivatives were synthesized. In some of these compounds, two boradiazaindacene derivatives were placed cofacially, resulting in significant inter-chromophoric interactions, including excimer emission. A simple modification of boradiazaindacene structure leads to formation of an ICT dye, which has distinct spectral properties. Energy transfer between two BODIPY dyes was demonstrated as well. In addition, the spectral properties of ICT dye can be modulated by the addition of the acid leading to an acid switchable, energy transfer cassette. (c) 2005 Elsevier Ltd. All rights reserved.