Fig. 3: UV–Vis spectral traces of the stepwise photochromic reactions of complex 1.

a Photocyclization reaction of 1-oo to form 1-oc upon excitation of visible light at ca. 440 nm. b Photocyclization reaction of 1-oc to form 1-cc upon UV excitation at ca. 300 nm. c Photocycloreversion reaction of 1-cc to form 1-co upon excitation of visible light at ca. 500 nm. d Photocycloreversion reaction of 1-co to form 1-oo upon excitation of visible light at ca. 580 nm. e Simultaneous photocyclization reactions of 1-oo to form 1-cc upon UV excitation. f Simultaneous photocycloreversion reactions of 1-cc to form 1-oo upon excitation of visible light at ca. 550 nm.