<p>Construction of electron donor-acceptor (D-A) conjugated system is an established strategy for achieving reverse saturable absorption (RSA) and broadband optical limiting (OL). Nevertheless, organic materials exhibit OL ability across the visible to near-infrared-II spectra range remain scarce. Herein, a series of D-A type <i>π</i>-conjugated copolymers with ultra-narrow bandgaps (0.62–0.76 eV) and strong ICT absorption were synthesized by coupling electron-withdrawing block [1,2,5]thiadiazolo[3,4-<i>g</i>]quinoxaline (TQ) with various electron-donating groups (thiophene, selenophene, bithiophene, di(thiophen-2-yl)ethene, and thienothiophene for <b>P1–P5</b>, respectively). <i>Z</i>-scan experiments reveal that all copolymers exhibit RSA behaviours at both 532 and 1064 nm, while <b>P1, P3</b> and <b>P4</b> maintain RSA performance extending to 1600 nm. Among all copolymers, <b>P5</b> exhibits the strongest RSA performance upon both 532 and 1064 nm laser pulses, with the highest nonlinear absorption coefficient (<i>β</i>_eff) of 51.5 and 49.4 cm·GW⁻¹, respectively, and the lowest OL onset fluence (<i>F</i>_on) of 0.31 and 0.38 J·cm⁻², respectively. In contrast, <b>P4</b> shows optimal RSA property at 1600 nm laser pulse, with <i>β</i>_eff of 13.1 cm·GW⁻¹ and <i>F</i>_on of 1.43 J·cm⁻², respectively. Combining the results of <i>Z</i>-scan and UV-Vis-NIR experiments, it can be speculated that moderate ground-state absorption, rather than excessively strong absorption, favors superior RSA properties. This work offers valuable insights for designing copolymers with excellent RSA behavior, as well as presents a class of candidate material systems for ultrabroadband optical limiting.</p>