Singlet fission (SF) has been proven to be an effective strategy to overcome the Shockley–Queisser limit of photovoltaics. However, the materials suitable for SF are relatively rare due to the strict requirements for the occurrence of this process. In the present study, we report the first preparation of two heteroatoms (O and S)-doped polycyclic aromatic hydrocarbons (PAHs) molecules with (β, β) connected furan/thiophene ring. The optical and physiochemical properties of both compounds are investigated by a variety of spectroscopies, including UV–vis absorption, photoluminescence and cyclic voltammetry. In addition, their ultrafast excited state dynamics are studied by femtosecond transient absorption. Experimental data showed that the singlet fission efficiency was improved by 2 times when replacing oxygen with sulfur atom, which could provide some guidelines in designing singlet fission materials with better efficiency.