. . . "The photolabile linking group is represented by the formula: ##STR10## in which R1 is C1 -C8 alkyl, aryl or aralkyl; R2, R3 and R4 are each independently hydrogen, C1 -C8 alkyl or C1 -C8 alkoxy; X31 is halogen, --OH, --OP, --SH, --SP, or --NHP and Y31 is Br, Cl, OH, NH2, SH, OP, SP and NHP, wherein P is a protecting group; and q is an integer of from 1 to 10." .