Microoptical spectroscopy of BiI3 molecules adsorbed in nano-channels of zeolite single crystals

Absorption spectra are reported for BiI3 molecules incorporated into channels of zeolite MOR and AFI. Polarized absorption spectra for the zeolite single crystals, of size about 50 μm, were measured by means of microoptical spectroscopy. The absorption spectrum of BiI3 in MOR is different from that observed in LTA, and also shows a polarization dependent on the direction of the channel. The BiI3 molecule is expected to have nearly C3v symmetry even in the MOR channels, and has a preferred orientation of the molecular axis along the channel. On the other hand, no polarization dependence of BiI3 is observed in the AFI channel, although AFI has a channel size similar to that of MOR. The cations and the framework induce the electric field inside the MOR channels, which acts as an adsorption potential for molecules. The experimental results indicate that the electric field plays an important role in the molecular orientation.