Photophysics of 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine in micelles: selective dual fluorescence in sodium dodecylsulphate and Triton X-100.

The photophysical behavior of 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b) has been studied in nonionic triton X-100 (TX-100), cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecylsulfate (SDS) micelles using steady state and time resolved fluorescence techniques. The molecule emits both normal and TICT fluorescence in SDS and TX-100 but emits only normal fluorescence in CTAB. This difference in behavior of the fluorophore is due to varying extent of hydrogen bonding experience by it in different micelles. Of the three possible monocations, only two kinds of monocations, MC1 (formed by protonation of pyridine ring nitrogen) and MC2 (formed by the protonation of imidazole nitrogen) are present in all the micelles (Scheme 1). DFT calculations performed on the monocations reveal that MC1 and MC2 are more stable than MC3, the monocation formed by the protonation of dimethylamino nitrogen.