The fluorescent properties of MIL-53(Al)-TDC are drastically changed due to the presence of iodine, even in small quantities, as a result of an energy transfer process from the host material (MIL-53(Al)-TDC) to the guest molecule (I2). While MIL-53(Al)-TDC's emission spectrum shows a weak and broad band, after I2 adsorption, it exhibits well-resolved and long-lasting emission lines, which could be exploited for iodine detection. Density Functional Theory periodical calculations demonstrated that in the most stable MIL-53(Al)-TDCI2 configuration, the I2 molecule is bonded mainly by an O-HI hydrogen bond. The QTAIM showed that other non-covalent interactions also provided stability to MIL-53(Al)-TDCI2. The electrostatic potential analysis indicated that the I2 molecule adsorption occurs by a combination of specific interactions with a strong electrostatic contribution and weak interactions. These results postulate fluorescent MIL-53(Al)-TDC as an efficient I2 detector (potentially for radioactive I2), using a simple fluorimetric test.