the 7-alkynylated 8-aza-7-deazaadenine (pyrazolo[3,4-d]pyrimidin-4-amine) 2′-deoxyribonucleosides are rather weakly fluorescent (Table 4). Quantum yields and fluorescence decay times are measured. The synthesis of the 7-alkynylated 7-deaza-2′-deoxyadenosines and 8-aza-7-deaza-2′-deoxyadenosines was performed with 7-deaza-2′-deoxy-7-iodoadenosine (6) or 8-aza-7-deaza-2′-deoxy-7-iodoadenosine (22) as