Molecular crystals energy transfer

The lowest excited states in molecular crystals are singlet and triplet excitons [3]. Since it costs coulombic energy to transfer an electron that has been excited optically from the HOMO (highest occupied molecular orbital) to the LUMC)... 

The behaviour, which is not controlled by the topochemical rule but is greatly influenced by non-topochemical factors, is discussed in Section 2 in terms of molecular mobility, stabilization energy by orbital interaction and energy transfer in the crystals. 

From the results of the fluorescence spectroscopic study it is concluded that excitation energy at the lowest excited state of a PDA derivative having a thioester moiety is localized at the thioester group intra- or inter-molecular energy transfer from the conjugated system of the PDA to the thioester moiety must have occurred in the crystalline state to afford a photostable crystal (Hasegawa et al., unpublished data). 

At present it is universally acknowledged that TTA as triplet-triplet energy transfer is caused by exchange interaction of electrons in bimolecular complexes which takes place during molecular diffusion encounters in solution (in gas phase -molecular collisions are examined in crystals - triplet exciton diffusion is the responsible annihilation process (8-10)). No doubt, interaction of molecular partners in a diffusion complex may lead to the change of probabilities of fluorescent state radiative and nonradiative deactivation. Nevertheless, it is normally considered that as a result of TTA the energy of two triplet partners is accumulated in one molecule which emits the ADF (11). Interaction with the second deactivated partner is not taken into account, i.e. it is assumed that the ADF is of monomer nature and its spectrum coincides with the PF spectrum. Apparently the latter may be true when the ADF takes place from Si state the lifetime of which ( Tst 10-8 - 10-9 s) is much longer than the lifetime of diffusion encounter complex ( 10-10 - lO-H s in liquid solutions). As a matter of fact we have not observed considerable ADF and PF spectral difference when Sj metal lo-... 

Switching systems based on photochromic behavior,I29 43,45 77-100 optical control of chirality,175 76 1011 fluorescence,[102-108] intersystem crossing,[109-113] electro-chemically and photochemical induced changes in liquid crystals,l114-119 thin films,170,120-1291 and membranes,[130,131] and photoinduced electron and energy transfer1132-1501 have been synthesized and studied. The fastest of these processes are intramolecular and intermolecular electron and energy transfer. This chapter details research in the development and applications of molecular switches based on these processes. 

In this thesis, we will focus on molecules as individual wires. It is, nevertheless, important to point out, that electron and energy transport in higher dimensional molecular materials (such as polymers or molecular crystals) is closely interconnected. Many of the mechanisms that have been discussed in this thesis, such as coherent tunneling, thermal hopping, Forster transfer, etc., are present in both the single-wire systems and in molecular materials. 

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