Heterocyclic Substituted Arenediazonium Salts with a Long‐wave‐length Range of Sensitivity. II. 4‐(1‐Heterocycliden‐2,3‐diaza‐prop‐2‐en‐3‐yl)‐arenediazonium tetrafluoroboratesThe title compounds (3) are obtained by reaction of aromatic bis‐diazonium salts with substituted 2‐benzylidene‐1,3‐dithioles and 2‐benzylidene‐1,3‐diselenole, respectively. The maximum of the long wave‐length absorption band of3varies from 580 nm up to 665 nm depending on the structure of the compound.The quantum yields of the photolysis of the diazonium salts3are low (1 · 10−4to 7 · 10−3). The azo dyes obtained from3with usual azo‐couplers absorb in a shorter wave‐length range than the corresponding d