The invention provides compositions and methods for improved hybridization analysis utilizing DNA, RNA, PNA and chimeric oligomers in which one or more purine bases are substituted by a pyrazolo[5,4-d]pyrimidine or by a 7-deazapurine purine analogue. Reduced self-aggregation and reduced fluorescence quenching are obtained when the oligomers are used in various methods involving hybridization. Methods of synthesis, as well as novel synthetic precursors, are also provided.