Mono-arylated HIs such as 1 are strongly photochromic in solution with maxima separation between the two switching isomers reaching more than 30 nm in monomeric MA. However, within the polymer matrix, the photochromism is markedly reduced, and photodegradation occurs soon after light irradiation (Fig ). HI derivative 2 inheriting increasing electron donation at the stilbene-fragment does not deliver a significantly better absorption band separation between the E/Z isomers (Fig ) but no photodegradation is visible from the spectra. However, visible color paling in the PMA material still indicates photodegradation after prolonged irradiation durations with light of 470 nm. For HI derivative 3 (Figure ), which differs from compound 2 by a chlorine substituent in ortho-position to the dimethylaniline and para-position to the methoxy substituents, again photodegradation occurs soon after irradiating the samples. Irradiating the very electron rich julolidine substituted HI 4