To approach this seemingly intractable problem, we have developed a new molecular design utilizing a fused carbazole (indolocarbazole, ICz) in combination with a phthalimide (PI) acceptor unit, in fully planar rigid molecular structures (ICz-PI; Figure ) giving efficient TADF. In the context of triplet harvesting, phthalimides are particularly useful as they give efficient π-π * and n-π* intersystem crossing. In addition, they are relatively weak donors and acceptors with significantly high triplet energies, ideal for blue-emitting charge-transfer systems. Furthermore, two isomers of ICz-PI which differ in the position of N-C and C-C bonds connecting the donor-acceptor fragments, exhibit very different excited state behaviour and photophysics. Most importantly, these emitters show stable ICT states and triplet harvesting properties both in solution and doped solid films with good photoluminescence quantum yields. We propose a mechanism that explains how conjugation is broken in the excited state of these ICz-PI molecules such that planar ICT states are stabilised to give long CT prompt lifetimes of >30 ns and persistent TADF. Our observations break new ground in showing that it is possible; (i) to stabilise ICT states in a fully-planar conjugated rigidified molecule and (ii) to achieve TADF without orthogonal D-A or highly spatially separated D and A units.