AB-INITIO MO AND X-RAY STUDIES OF EXCITED-STATES IN MOLECULAR-CRYSTALS OF TA-DICYANOVINYL)-3-METHYL-N-METHYL-N-BENZYLANILINE

The excited state of ta-dicyanovinyl)-3-methyl-N-methyl-N-benzylanilin e (DCBA) in two types of molecular crystals, orange and yellow crystal s, are investigated. These crystals were structurally analyzed by mean s of X-ray diffraction techniques. In each crystal, DCBA forms one-dim ensional infinite chain by pi-interactions between the 4-(beta,beta-di cyanovinyl)aniline planes. The orange crystal involves only one type o f infinite chain. On the other hand, interestingly, the yellow crystal contains two kinds of different infinite chains, which are distinguis hed by the degree of pi-overlap between the neighboring molecules. Onl y the crystalline forms of DCBA show fluorescence. The fluorescence ti me decay of the orange crystal contains only one decay component and i ts lifetime was 52.7 ns. On the other hand, that of the yellow crystal consists of two decay components, and the lifetimes were 7.0 and 16.8 ns. In each crystal, the number of the decay components are in agreem ent with the number of the independent infinite chains. The nature of the excited states is investigated by use of simple ab initio STO-3G m olecular orbital (MO) calculations. It is suggested from the MO calcul ations that the delocalized excited states are formed in the orange cr ystal, on the other hand, the excited states of the yellow crystal are characterized by the localized excitation.