A specific intramolecular interaction in a bis(2-thienyl)maleimide derivative

3,4-Bis(4-ethoxycarbonyl-3-hydroxy-5-methyl-2-thienyl)-1-phenyl-1H-pyrrole-2,5-dione shows no photochromism in the crystalline state, despite its typical "photochromic" structure (X-ray diffraction data): the anti-parallel orientation of the thienyl fragments relative to the plane of pyrrole-2,5-dione and a short distance between potential reactive sites (C(3')...C(3'A), 3.27 ). The absence of photochromism was explained by a specific attractive interaction between the O atoms of the maleimide ring and the thiophene S atoms, which can preclude UV-induced photocyclization.