| Abstract
| - Control of emission by intermolecular fluorescence resonant energy transfer (IFRET) and intermolecular chargetransfer (ICT) is investigated with the quantum-chemistry method using two-dimensional (2D) and three-dimensional (3D) real space analysis methods. The work is based on the experiment of tunable emissionfrom doped 1,3,5-triphenyl-2-pyrazoline (TPP) organic nanoparticles (Peng, A. D.; et al. Adv. Mater.2005,17, 2070). First, the excited-state properties of the molecules, which are studied (TPP and DCM) in thatexperiment, are investigated theoretically. The results of the 2D site representation reveal the electron−holecoherence and delocalization size on the excitation. The results of 3D cube representation analysis reveal theorientation and strength of the transition dipole moments and intramolecular or intermolecular charge transfer.Second, the photochemical quenching mechanism via IFRET is studied (here “resonance” means that theabsorption spectrum of TPP overlaps with the fluorescence emission spectrum of DCM in the doping system)by comparing the orbital energies of the HOMO (highest occupied molecular orbital) and the LUMO (lowestunoccupied molecular orbital) of DCM and TPP in absorption and fluorescence. Third, for the DCM−TPPcomplex, the nonphotochemical quenching mechanism via ICT is investigated. The theoretical results showthat the energetically lowest ICT state corresponds to a pure HOMO−LUMO transition, where the densitiesof the HOMO and LUMO are strictly located on the DCM and TPP moieties, respectively. Thus, the lowestICT state corresponds to an excitation of an electron from the HOMO of DCM to the LUMO of TPP.
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