8-Furyl­imidazolo-2′-de­oxy­cytidine: crystal structure, packing, atropisomerism and fluorescence

8-Furyl­imidazolo-2′-de­oxy­cytidine ((fur)ImidC), C(14)H(14)N(4)O(5), is a fluorescent analogue of 2′-de­oxy­cytidine, also displaying the same recognition face. As a constituent of DNA, (fur)ImidC forms extraordinarily strong silver-mediated self-pairs. Crystal structure determination revealed that (fur)ImidC adopts two types of disordered residues: the sugar unit and the furyl moiety. The disorder of the sugar residue amounts to an 87:13 split. The disorder of the furyl ring results from axial chirality at the C8—C2′′ bond connecting the nucleobase to the hetero­cycle. The two atropisomers are present in unequal proportions [occu­pancies of 0.69 (2) and 0.31 (2)], and the nucleobase and the furyl moiety are coplanar. Considering the atomic sites with predominant occupancy, an anti conformation with χ = − 147.2 (7)° was found at the glycosylic bond and the 2′-de­oxy­ribosyl moiety shows a C2′-endo (S, (2) T (1)) conformation, with P = 160.0°. A (1)H NMR-based conformational analysis of the furan­ose puckering revealed that the S conformation predominates also in solution. In the solid state, two neighbouring (fur)ImidC mol­ecules are arranged in a head-to-tail fashion, but with a notable tilt of the mol­ecules with respect to each other. Consequently, one N—H⋯N hydrogen bond is found for neighbouring mol­ecules within one layer, while a second N—H⋯N hydrogen bond is formed to a mol­ecule of an adjacent layer. In addition, hydrogen bonding is observed between the nucleobase and the sugar residue. A Hirshfeld surface analysis was performed to visualize the inter­molecular inter­actions observed in the X-ray study. In addition, the fluores­cence spectra of (fur)ImidC were measured in solvents of different polarity and viscosity. (fur)ImidC responds to microenvironmental changes (polarity and viscosity), which is explained by a hindered rotation of the furyl residue in solvents of high viscosity.