Light-emitting diodes based on metal halide perovskites (PeLEDs) with high 26 colour quality and facile solution processing are promising candidates for full27 colour and high-definition displays1-4. Despite the great success achieved in green 28 PeLEDs with lead bromide perovskites5, it is still challenging to realise pure-red 29 (620-650 nm) LEDs using iodine-based counterparts, as they are constrained by 30 the low intrinsic bandgap6. Here, we report efficient and colour-stable PeLEDs 31 across the entire pure-red region, with a peak external quantum efficiency (EQE) 32 reaching 28.7 per cent at 638 nm, enabled by incorporating a double-end anchored 33 ligand molecule into pure-iodine perovskites. We demonstrate that a key function 34 of the organic intercalating cation is to stabilise lead-iodine octahedron through 35 coordination with exposed lead ions and enhanced hydrogen bonding with iodine, 36 which synergistically facilitates spectral modulation, promotes charge transfer 37 between perovskite quantum wells and reduces iodine migration under electrical 38 bias. We realise continuously tunable emission wavelengths for iodine-based perovskite 39 films with suppressed energy loss caused by the decrease in bond 40 energy of lead-iodine in ionic perovskites as the bandgap increases. Importantly, 41 the resultant devices show outstanding spectral stability and half-lifetime 42 of >7,600 minutes at an initial luminance of 100 cd m-2.