Organic conjugated materials with strong electronic-vibration coupling encounters significant reorganization energy (λ) between neutral and ionized states, which affects their charge transport and exciton delocalization and binding energy. There is a strong need to understand the relationship between material structures and λ in order to facilitate more efficient charge generation and better mitigation of energy loss in organic solar cells. Recently, Jen et al. have shown that by extending the conjugation length of ladder-type donors in D-A alternating copolymers facilitates π-electron delocalization and reduces optical band-gap. The rigid, coplanar structures can also prevent rotational disorder to enhance charge separation and carrier mobility. By extending the 5-ring IDT to 7-ring IDTT, one-order higher hole and electron mobilities and significantly improved PCE (~8% compared to 6%) can be achieved.2 The IQE of these polymers can also reach >90%, which indicates this may be a good avenue to optimize molecular structures to improve device performance.3 Herein, we have synthesized a series of model compounds with systematically increased donor unit size to study if the enhanced conjugation length and rigid backbone will affect their reorganization energy, exciton delocalization, and film morphology to facilitate photo-to-electron conversion. These model compounds will also facilitate theoretical and spectroscopic studies to understand the relationship between bound excitons, charge transfer, and charge separation for achieving higher PCE. The initial results derived from these model compounds have shown red-shifted absorption and emission from 5-ring (IDT) such as 7-ring (IDTT), 10-ring (IDTIDT), 11-ring (IDTCPDT), and finally, 12-ring (IDTIDTT). By copolymerizing these units with properly chosen acceptors, a vast array of D-A copolymers can be obtained to systematically study the relationship between reorganization energy and charge generation and transport.