The quantum yield of reverse photoisomerization is comprised between 1.5 and 5 times those of the direct switch, as it was estimated from Z-isomers absorbance spectra (see experimental part, Figures S10-S13 and Table ). Finally, those values are lower than those reported for similar stilbenes derivatives (Φ !" = 0.2-0.6, Φ "! = 0.3-0.5) or azobenzenes (Φ !" = 0.1-0.5, Φ "! = 0.2-0.6). Interestingly, absolutely no evidence of photoisomerization has been detected for the series 6a-6d, neither by NMR nor UV/Vis. Thus, the existence of competitive relaxation channels was considered. For these reasons, and due to the relevance of PTT, the photoinduced temperature increase was monitored for this series of compounds.