N,N-Dialkylaniline-Substituted tetraethynylethenes: A new class of chromophores possessing an emitting charge-transfer state. Experimental and computational studies.

The photophysical properties of N,N-dimethylaniline- (DMA) substituted tetr aethynylethene RTE; 3,4-diethynylhex-3-ene-1,5-diyne and related derivative s were investigated in a joint experimental and computational study. Measur ements of the electronic emission spectra showed that these novel chromopho res display a dual fluorescence which strongly depends on solvent polarity. Computational studies suggest that the twisted intramolecular charge-trans fer state TICT) model offers a possible explanation for the experimentally observed dual fluorescence. rime-dependent density functional calculations revealed that the initial excited state reached upon photoirradiation relax es to a lower-energy TICT state in which either the dimethylamino group is twisted into an orthogonal position with respect to the remaining planar ar ylated TEE moiety or the entire DMA donor group takes an orthogonal orienta tion with respect to the rigid, planar TEE acceptor moiety. For the compoun ds investigated the charge-transfer state responsible for the strongly solv ent-dependent luminescence is directly connected with the initial excited s tate, namely, no crossing of states is involved.