Journal Article Review C = C cross‐linkable units conjugated polymers coplanar conformation cross‐linking crystallinity deep blue deep-blue polymer light-emitting diodes deep‐blue flexible polymer light‐emitting diodes elastic‐plastic fully π‐conjugated polymer excellent energy dissipation capacity excited matter flexible electroluminescent devices flexible polymer light‐emitting diodes internal plasticization strategy intrinsically stretchable π-conjugated polymers large‐area printed display optoelectronic applications optoelectronic devices organic conjugated molecules polyfluorene self-encapsulated strategy semiconductor fluid plasticizing side‐chain internal plasticization single‐chain emission behavior solution‐processable strain tolerance capacity stretchable electroluminescent films stretchable fully π‐conjugated polymers film