Polymorphism-Dependent Emission for Di(p-methoxylphenyl)dibenzofulvene and Analogues: Optical Waveguide/Amplified Spontaneous Emission Behaviors

The synthesis and optical investigations of di(p-methoxylphenyl)dibenzofulvene (1) and its analogues 2, 3, 4, 5, 6, and 7 with different lengths of alkoxyl chains are presented. All of these molecules exhibit emission in the solid state. The following interesting properties are reported for compound 1 : 1) the solid-state fluorescence of 1 is dependent on the polymorphism forms; the two crystalline forms 1a and 1b are strongly blue- and yellow-green-emissive, whereas the amorphous solid is weakly fluorescent with orange emission; 2) on the basis of crystal-structural analysis, the intermolecular interactions will restrict the internal rotations, leading to fluorescence enhancement for the two crystalline forms 1a and 1b; however, the difference in emission color between 1a and 1b is ascribed to the molecular conformational alteration; 3) the solid-state fluorescence of 1 can be tuned by heating and cooling as well as grinding. Importantly, microrods of 1a and 1b exhibit outstanding optical waveguide behaviors. Moreover, amplified spontaneous emission for 1b and multimode-lasing behavior for 1a are presented. Besides the studies of compound 1, the crystal structures and solid-state fluorescence behaviors of 2, 3, 4, 5, 6, and 7 are also described.