Photochromic properties of six 5-O-<i>n</i>-alkyl,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="$6'$" id="E1"><mml:msup><mml:mn>6</mml:mn><mml:mo>′</mml:mo></mml:msup></mml:math>-CN substituted spironaphthoxazines
International journal of photoenergy