They have the general chemical formula CZ2, where Z = O, S, Se, Te.
[1][2] This includes: Double bonds between carbon and chalcogen elements, C=Z, become weaker the heavier the chalcogen, Z.
This trend means carbon dichalcogenide monomers are less stable and more susceptible to polymerisation as Z changes from O to Te.
For example, CO2 is stable, CS2 polymerises under extreme conditions, CSe2 tends to polymerise, CSeTe is unstable and CTe2 does not exist.
[1] This trend is an example of the double bond rule.