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International audience; The excitation decay kinetics of polar Indandione-1,3 Pyridinium Betaine (IPB) molecules in various environments: solvents, films and crystals, were studied using time-resolved luminescence and transient absorption measurements. A red-shift, depolarization and fast decay of the luminescence intensity were observed on a femtosecond time scale in dilute solutions and explained by excitation relaxation from the initially created intramolecular charge transfer state to the lower energy excited state of the indandione moiety. The first fast relaxation stage is followed by a slower one responsible for the relaxation to the ground state stage with the rate depending on the viscosity of the surrounding. By comparing the excitation properties of IPB in solution and those in the crystal form, the influence of the intermolecular interactions on the excited state dynamics is revealed. Excitation relaxation in the IPB deposited films of different thickness and in a single crystal is described as a competition between different relaxation paths of nonradiative recombination, these paths being the high lying Frenkel exciton states and the low lying intermolecular charge transfer states.

The paper addresses the spectroscopic peculiarities of polar molecular crystals and films of dimethylaminebenzylidene-1,3-indandione (DMABI). Specific visible fluorescence bands for various modifications of the system are discovered. They are identical for all excitation conditions and seem to be correlated with the structural organization of the media. The infrared excitation of these bands is shown to be a two-step process which turns into the saturating regime at higher intensities.