Pentacyclic adenine: a versatile and exceptionally bright fluorescent DNA base analogue by Bood, M, Füchtbauer, AF, Wranne, MS, Ro, JJ, Sarangamath, S, El-Sagheer, AH, Rupert, DLM, Fisher, RS, Magennis, SW, Jones, AC, Höök, F, Brown, T, Kim, BH, Dahlén, A, Wilhelmsson, LM, Grøtli, M