In situ low-temperature Raman studies of iodine molecules confined in the one-dimensional channels of AlPO4-5 crystals

• We have found that the orientation of individual iodine molecules in the channels of AlPO4-5 (AFI) crystals prefer to lie along channel axis as temperature decreases.
• Such temperature-induced orientation transformation is reversible upon heating up to room temperature.
• The porous medium plays an important role in manipulating and controlling the orientation of individual iodine molecules.

We have performed in situ low-temperature Raman spectroscopy studies on iodine molecules confined in the one-dimensional (1D) round channels of AlPO4-5 (AFI) crystals. Polarized Raman measurements show that the Raman intensity of individual iodine molecules parallel to channel axis (termed lying molecules) increases more than that of iodine molecules perpendicular to channel axis (termed standing molecules) upon cooling temperature down to −196 °C. This suggests that an orientation transformation of individual iodine molecules has occurred to increase the population of iodine molecules lying along channel axis as temperature decreases. Consequently, the corresponding Raman mode shows a redshift due to the enhancement of intermolecular interaction. This low-temperature induced orientation transformation is observed to recover when heated back to room temperature, indicating that orientation of iodine molecules confined in this porous medium can be modulated reversibly at a molecular level by cooling temperature down.

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