Novel fluorescent pH sensors and a biological probe based on anthracene derivatives with aggregation-induced emission characteristics.

Three functionalized 9,10-distyrylanthracene (DSA) derivatives, namely, 9,10-bis(4-hydroxystyryl)anthracene (2), 9,10-bis{4-[2-(diethylamino)ethoxy]styryl}anthracene (4), and 9,10-bis{4-[2-(N,N,N-triethylammonium)ethoxy]styryl}anthracene dibromide (5), were synthesized and their fluorescence properties were investigated. The three DSA derivatives possess a typical aggregation-induced emission (AIE) property (i.e., they are nonluminescent in dilute solutions but are efficiently fluorescent as induced by molecular aggregation). Different AIE properties were tuned through molecular structure control. Dye 2 is a phenol-moiety-containing compound, which shows aggregation at pH values smaller than 10, resulting in a high fluorescence intensity. Thus, dye 2 has a pK(a) of 9.94. 4 is an amine-containing compound that starts to aggregate at slightly basic conditions, resulting in a pK(a) of 6.90. Dye 5 is an ammonium-salt-containing compound. Because it is very soluble in water, this compound has no AIE phenomenon but can interact strongly with protein or DNA to amplify its emission. Therefore, 5 is a fluorescent turn "on" biological probe for protein and DNA detection and it is also selective, which works for native BSA and ct DNA but not their denatured forms. Therefore, we not only developed a few new compounds showing the AIE phenomena but also controlled the AIE through environmental stimulation and demonstrated that the new AIE molecules are suitable for pH and biomacromolecule sensing.