Development of molecular tweezers depends on the design and synthesis of reliable spacers. Two new classes of spacers based on functionalized dibenzo [a, j] xanthene are described. Molecular tweezers 4, 5 and 6 with adjustable cavity are designed and synthesized. Single crystal X-ray diffraction shows self-assembly and recognition of 4 in the solid state; with the π-stacking, CH/O and CH/π interactions being the driving forces. The ...