The present invention is a method of producing a 3-hydroxymethyl-benzobthiophene derivative without the possible concomitant formation of isomers, which comprises selectively cyclizing a sulfoxide having X shown in the reaction scheme below: . In exemplary embodiments, the particle detection system includes at least one detector and a light source that provides light. The display element is characterized in that the electrolytic layer substantially contains no iodine ion and at least two pixels having different degree of blackening are subjected to whitening reset driving simultaneously in the driving operation.