Thermally irreversible photochromic systems. Reversible photocyclization of 1,2-bis (2-methylbenzo[b]thiophen-3-yl)perfluorocyclocoalkene derivatives

1,2-Bis(2-methylbenzo[b]thiophen-3-yl)perfluorocylopentenes undergo thermally irreversible photochromic reactions in which colouration/decolouration cycles can be repeated more than 104 times without significant loss of performance.