A method for labeling null-amyloid plaques and neurofibrillary tangles in vivo and in vitro, comprises contacting a compound of formula (I): 1 with mammalian tissue. In formula (I), R1 is selected from the group consisting of nullC(O)-alkyl, nullC(O)-alkylenyl-R4, nullC(O)O-alkyl, nullC(O)O-alkylenyl-R4, nullCnullC(CN)2-alkyl, nullCnullC(CN)2-alkylenyl-R4, 2 R4 is a radical selected from the group consisting of alkyl, substituted alkyl, aryl and substituted aryl; R5 is a radical selected from the group consisting of nullNH2, nullOH, nullSH, nullNH-alkyl, nullNHR4, nullNH-alkylenyl-R4, nullO-alkyl, nullO-alkylenyl-R4, nullS-alkyl, and nullS-alkylenyl-R4; R6is a radical selected from the group consisting of nullCN, nullCOOH, nullC(O)O-alkyl, nullC(O)O-alkylenyl-R4, nullC(O)-alkyl, nullC(O)-alkylenyl-R4, nullC(O)-halogen, nullC(O)NH2, nullC(O)NH-alkyl, nullC(O)NH-alkylenyl-R4; R7 is a radical selected from the group consisting of O, NH, and S; and R8 is N, O or S. R2 and R3 are each independently selected from the group consisting of alkyl and alkylenyl-R10, wherein R10 is selected from the group consisting of nullOH, nullOTs, halogen, spiperone, spiperone ketal and spiperone-3-yl. Alternatively, R2 and R3 together form a heterocyclic ring, optionally substituted with at least one radical selected from the group consisting of alkyl, alkoxy, OH, OTs, halogen, alkylenyl-R10, carbonyl, spiperone, spiperone ketal and spiperone-3-yl. In the compounds of formula (I), one or more of the hydrogen, halogen or carbon atoms can, optionally, be replaced with a radiolabel.