Spectroscopic study on excitonic interactions in hydrogen-bonded dusters in the gas phase

Frenkel型激子相互作用有两种类型：一种是强耦合情况，另一种是弱耦合情况。平面氢键二聚体和团簇中的激子相互作用还不清楚。用激光光谱方法研究了气相中氢键团簇中激子的相互作用。我们所研究的分子体系是7-氮杂吲哚二取代的7-氮杂吲哚二聚体（7AI_2）和1-氮杂咔唑二聚体（1AC_2）。我们已经测量了同位素异构体的电子光谱，未氘化的（hh），一个NH基团是氘代的（hd），和两个NH基团是氘代的（dd）。7AI_2hd在最低激发电子态（S_1）时，激发完全局域在一个单体单元（h *d或hd*）上，表明处于S_1态的7AI_2属于激子理论的弱耦合情况。激子相互作用导致的零点能级的分裂已被确定为1.2 cm-1<-1>。4-氯-7-氮杂吲哚二聚体和4-二甲氨基-7-氮杂吲哚二聚体的激子分裂值与7Al_2相近。7Al_2和1AC_2之间的差异是由于1AC_2的S_1态激子分裂较小。

It is known that there are two types of excitonic interaction in Frenkel type: One is strong coupling case and the other is weak coupling case. The excitonic interaction in planar hydrogen-bonded dimer and clusters has not been clarified. We have investigated excitonic interactions in the hydrogen-bonded clusters in the gas phase with laser spectroscopic methods. The molecular systems we studied are 7-azaindole dime substituted 7-azaindole dimers (7AI_2), and 1-azacarbazole dimer (1AC_2). We have measured the electronic spectra of isotopomers, undeuterated (hh), one of the NH groups is deuterated (hd) , and the two NH groups are deuterated (dd). In the case of 7AI_2hd the excitation is completely localized on one monomer unit (h *d or hd*) in the lowest excited electronic sate (S_1), indicating that the 7AI_2 in the S_1 state should be classified as a weak coupling case of the exciton theory. The splitting of the zero-point level due to excitonic interaction has been determined to be〜2 cm^<-1>. The excitonic splittings of 4-chloro-7-azaindole dimer and 4-dimethylamino-7-azaindole dimer are predicted to be similar values as 7AI_2. On the other hand, the excitation is not completely localized on one monomer moiety in 1AC_2-hd The difference between 7Al_2 and 1AC_2is due to smaller excitonic splitting in the S_1 state of 1AC_2.