Effect of halogen-bonding on dual fluorescence of 4-dimethylaminobenzonitrile

Complete text of publication follows. The solvent dependent dual fluorescence of 4-dimethylaminobenzonitrile (DMABN) originated from a locally excited state (LE) and twisted intramolecular charge transfer (TICT) state that is stabilized in polar solvents. It has been the subject of intense experimental and theoretical work since its discovery in 1959. It can be expected that DMABN can form a halogen-bonding complex with a halogen atom as Fig. 1. Herein the fluorescence of DMABN alone and with carbon tetrabromide (CBr4) or diiodoperfluorohexane was investigated in different solvents. Upon addition of CBr4 or diiodoperfluorohexane, both LE and TICT peak decreased, but TICT peak decreased more sharply, as showed in Fig. 2. The halogen-bonding may disturb the TICT state by CT between Br and N atom. Also Br quenches dual fluorescence by heavy atom effect. So fluorescence from TICT state decreased more quickly than that from LE state.