The present invention is directed to novel bifunctional CTI-CTI and CBI-CTI dimers of the formula: F1-L1-T-L2-F2 where F1, L1, T, L2 and F2 are as defined herein, useful for the treatment for proliferative diseases, where the inventive dimers can function as stand-alone drugs, payloads in antibody-drug-conjugates (ADCs), and linker-payload compounds useful in connection with the production or administration of such ADCs; and to compositions including the aforementioned dimers, linker-payloads and ADCs, and methods for using these dimers, linker-payloads and ADCs, to treat pathological conditions including cancer.