Study on pyrrole chalcone derivatives used for blue LED free radical photopolymerization: Controllable initiating activity achieved through photoisomerization property

•E-HP-1 and E-HP-3 efficiently initiates blue LED free radical photopolymerization in the presence of additive TEOA.•Z forms of pyrrole chalcones could completely isomerize back to their E forms upon LED@465 nm irradiation.•The photo-reactivity of initiating system based on E-HP-3 and its equilibrium could be controlled by the excitation of LED@465 nm light.