Fluorescence properties of organic dyes: quantum chemical studies on the green/blue neutral and protonated DMA-DPH emitters in polymer matrices

The absorption and fluorescence spectra of the green emitter DMA-DPH {1-[4-(dimethylamino)phenyl]-6-phenylhexa-1,3,5-triene} and its protonated blue-emitter form have been studied theoretically through time-dependent density functional theory (TD-DFT) and resolution-of-identity 2nd order perturbative coupled cluster (RI-CC2) calculations with basis sets up to augmented triple-ζ quality, in the gas phase and in solvents of different polarity. These systems dispersed in a polymer matrix are of interest for applications in organic light emitting diode devices (OLEDs). Calculations show that the observed absorption and emission spectra correspond to transitions between the S(0) and S(1) states, in both systems. The nature and characteristics of these transitions are discussed. Excellent agreement with experimental data is obtained, both for absorption and emission, provided that the state-specific polarized continuum model (SS-PCM) method is employed for the inclusion of the solvent.