The development of thermostable polyimides (PIs) is urgently required for application in traditional aerospace and newly designing flexible-display substrates. The root to obtain intrinsic heat-resistant PIs is to seek novel monomers. Based on the high bond energy of quinoxaline, several quinoxaline diamines, including 3/2-(4-aminophenyl)-2/3-quinoxalin-6-amine (QHDA), 3/2-(4-aminophenyl)-2/3-phenyl quinoxalin-6-amine (QBDA), and 3/2-(4-aminophenyl)-2/3-methylquinoxalin-6-amine (QMDA) were synthesized, and the corresponding PI films were prepared with four aromatic dianhydrides. The introduction of a quinoxaline moiety provided the PI films with excellent thermal properties and an advanced mechanical performance. The QHDA-PIs possessed a high thermal stability with a 5% mass-loss temperature (Td5%) of 528–560 °C, a glass-transition temperature (Tg) of 413–444 °C and a low coefficient of thermal expansion (CTE) of 1 ppm/K for QHDA-m because of its better linearity and closer packing. This study established design rules to tune the properties of quinoxaline PIs by side-group modification. Novel PI films with quinoxaline moiety exhibited advanced thermal properties and mechanical performance, which are promising potential for flexible display devices. Display omitted •Three phenylquinoxaline diamines containing different side groups were synthesized.•The polyimide containing quinoxaline showed excellent comprehensive properties.•The properties of polyimide can be adjusted by the side groups of phenylquinoxaline.•The red polyimide film can be obtained using phenylquinoxaline monomer with methyl.