Synthesis of Naphthalimide Derivatives and Their Luminescence upon Complexation with Cucurbit[ n ]uril Hosts.

A series of naphthalimide derivatives are synthesized and their binding behavior upon complexation with cucurbit[ n ]urils (CB[ n ]s) has been investigated. With a heavy atom (bromine) on the naphthalimide core, 4-bromo-1,8-naphthalimide derivatives 1 - 4 show short room-temperature phosphorescence (RTP) lifetimes with low quantum yields. Their RTP properties are significantly enhanced in the presence of CB[8] or CB[10] both in aqueous solution and solid state owing to the efficient suppression of nonradiative decay and isolation of quenching factors by the rigid cavity of CB[ n ]. Without the bromine atom, 1,8-naphthalimide derivatives 5 and 6 show strong excimer emission upon complexation with CB[10] accompanied by fluorescence transition from blue to cyan. The fluorescence colors of 4-(dimethylamino)-1,8-naphthalimide derivatives 7 and 8 change from blue to white to yellow with the addition of CB[ n ]. This host-guest complexation strategy to modulate the luminescence of the luminophore would further broaden the application of luminescent materials.