To concentrate pre-mesogens (molecules can convert to a mesophase quickly) from petroleum pitch and prevent system from suffering from excessive carbonization, the parent pitch was extracted by various solvents with different solubility parameters and the corresponding pitch residues were carbonized. It was found that the dispersive solubility parameter has a major effect on the FTIR structural indices (i.e., the indices calculated from Fourier transform infrared spectroscopy) of the pitch residue; thus, four pitch residues enriched in molecules characterized by different condensation degrees and numbers of alkyl chains were successfully obtained and their carbonization behaviors were identified to determine the carbonization behavior of pre-mesogens. The pitch residue obtained by hexamethylene extraction (A1HEX) formed a large domain texture with good lamellar orientation (d(002) = 3.4656 angstrom, Lc = 24.45 angstrom) and low softening point (SP = 257 degrees C) in a short carbonization time (6 h), which is attributed to the removal of molecules with a high alkyl carbon atom percentage (which accelerates the formation of an anisotropic phase) and the enrichment of specific molecules. The concentration of molecules with a low condensation degree (condensation index H-AU/C-A = 0.5491), fewer alkyl chains (C-H substitution indice, I-CHS = 0.1511), and a higher condensation reactivity in A1HEX accelerated the formation of the anisotropic phase and provided alkyl free radicals during thermal treatment, which hindered crosslinking between larger free radicals and contributed to the large domain texture with good lamellar orientation and a low softening point. In addition, because of the lower reactivity of the self-assembled polycyclic aromatic hydrocarbons (PAHs) contained in the anisotropic phase (compared to that of the isolated PAHs in the isotropic matrix), the rapid formation of a mesophase during carbonization prevented excessive condensation to some extent.