A series of phenylacetylenes and the meta-connected dendrimers were synthesized. Their UV absorption and fluorescence emission properties were discussed through the energy gap ΔE between HOMO and LUMO orbitals, the orbital diagrams and the charge densities of the related carbon atoms. The reason that the conjugation in the meta-connected phenylacetylenes and the meta-connected dendrimers is interrupted by the central benzene ring, but can be extended to the whole molecule in the para- and ortho- connected phenylacetylenes, possibly related to the charge density of the carbon atom to be located at the central benzene ring to connect the phenylethynyl branch. In the excited state, there is a coupling effect between the phenylethynyl branches connecting the same benzene ring. Therefore, the fluorescence emissions were red-shifted with increasing the number of phenylethynyl branches connecting the central benzene ring in the meta-connected phenylacetylenes, but not red-shifted with increasing the generation of the dendrimer.

Key words: synthesis, optical property, phenylacetylene, dendrimer, frontier orbital