Novel self-protective phosphorescence from crystalline nanoparticles assembled by 3-bromo- and 3-iodo-carbazoles...

The crystalline nanoparticles can be assembled by 3-bromo- and 3-iodo-carbazole (3-BrC and 3-IC) based on the halogen-halogen interaction in suspension aqueous solutions. As the colloid-like suspension was dropped onto film the particles further aggregate as rod-like structures with size of 3 microm in length and 1 microm in width. The halogen-halogen interaction are well proved by single crystal X-ray data, and the data reveal that each bromine atom interacts with the neighboring two, and each iodine atom interacts with the neighboring five and I-I interaction is stronger than that of Br-Br. Both 3-BrC and 3-IC can emit novel self-protective room temperature phosphorescence (RTP) in the range of 480 to near 800 nm at the excitation of 338 nm, and 3-BrC shows additionally the delayed fluorescence emission from 350 to 480 nm, both possessing the charge-transfer character caused by halogenations. RTP decay possesses the bi-exponential property and RTP lifetimes are 3.37, 31.16 ms (with ethanol) and 1.52, 30.83 ms (with THF) for 3-BrC or 3.53, 14.95 ms (with ethanol) and 1.68 ms, 13.74 ms (with THF) for 3-IC, showing " heavier atom ", I, makes intersystem crossing rate k(ISC) from both S1 to T1 and T1 to S(0) faster. For the results, the detection limits of 3-BrC and 3-IC can reach 2.4 x 10(-7) and 9.0 x 10(-8)mol L(-1), respectively, with wider linear range and higher precision compared with other systems.