Novel self-protective phosphorescence from crystalline nanoparticles assembled by 3-bromo- and 3-iodo-carbazoles based on halogen–halogen interaction in suspension solutions

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 μm in length and 1 μm 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 kISC from both S1 to T1 and T1 to S0 faster. For the results, the detection limits of 3-BrC and 3-IC can reach 2.4 × 10−7 and 9.0 × 10−8 mol L−1, respectively, with wider linear range and higher precision compared with other systems.