The photochromic properties of CyP-OBu were investigated in aprotic and protic solvents of various polarities (i.e. CHCl 3 , MeCN, DMSO, EtOH and H 2 O). The steady-state absorption spectra are shown in Error! Reference source not found. and correspond mainly to the E-isomer (>95%) as determined from NMR, and as expected. Except from water, all spectra exhibit three broad absorption peaks, centered at around 288, 327 and 374 nm, similar to the ones of natural cyclocurcumin or CyP. The highest and the lowest energy absorption band were assigned to the pp* transition of the phenyl-pyrone moiety and the styryl-pyrone moiety, respectively (Figure ), while the intermediate energy absorption band was assigned to an np* transition. This is consistent with the fact that the additional double bond in the pyrone cycle from CyP is not inducing any extension of the p-conjugation on the styryl-pyrone moiety, as compared to the dihydropyranone cycle from CC. Instead, it is favoring an extension of the planarity from one extreme to the other of the molecule as already observed for the parent CyP compound. A slight negative solvatochromism (Table ), accompanied by a narrowing of the vibrational band, is observed as solvent polarity decreases, and a slight dependency of the molar extinction coefficient (e, Table ) with the solvent should be pointed out. Despite ultrasonication and addition of 2v% of DMSO, CyP-OBu was not fully solubilized in the water and therefore the value of e is underestimated for this solvent.