To validate our hypothesis, we conduct temperature-dependent UV-vis absorption spectroscopy to reveal the solvent selectivity towards polymer backbone and use solution SAXS technique coupled with Hansen solubility parameter (HSP) theory to unravel the side-chain selectivity of the solvents. As shown in Figure , the room-temperature (RT) UV-vis absorption spectrum in all solvents consist of a prominent low-energy band (centered at around 700 nm) with a pronounced vibronic structure, followed by a lower-intensity UV-vis band (centered at around 415 nm). The low-energy band consists of a 0-0 and a 0-1 vibronic peak at around 720 nm and 655 nm, respectively. The presence of such a vibronically well-structured low-energy band is indicative of an ordered planar chain conformation, standing in contrast to an unstructured, featureless band usually observed from polymer chains with a disordered coiled backbone conformation . We hypothesize that such an ordered conformation of PII-2T chains is a result of aggregation induced chain planarization, as PII-2T indeed aggregates in all three types of solvents as discussed above. The aggregation mechanism in those three classes of solvents, however, can be different considering the solvent selectivity. This is further confirmed by our temperature-dependent study. As shown in Figure , temperature-dependent UV-vis absorption spectra are collected every ten degree Celsius by heating solutions from RT; the 0-0 peak intensity is obtained by multipeak fitting (Figure ) and is subsequently plotted versus temperature in various solvents (Figure ). The three classes of solvents give distinct spectra changes upon heating, which reveals different disaggregation behaviors of polymers due to solvent selectivity. In mutual solvents such as DCB, the low-energy absorption band exhibits a blue-shift together with a drop in its intensity with increasing temperature. In particular, the 0-0 peak intensity drops more quickly than the 0-1 peak. These changes reflect the disruption of conjugation along the polymer backbone caused by heating, namely the backbone conformation gradually becomes more disordered (i.e., less planarized) as temperature increases. In backbone-selective solvent CN, while the low-energy absorption band blue-shifts with temperature, its intensity does not drop abruptly until the solution temperature reaches the side chain melting temperature (Tm ~ 72 °C). The drop in 0-0 peak intensity after side chain melting is steeper than that in mutual solvents as shown in Figure . At high temperature (above 115 °C), the low-energy absorption band becomes featureless and the micron size aggregates disappear under optical microscope (Figure ), indicating there is a backbone conformational change to more coiled as the needle-like aggregates dissolve. This is consistent with our hypothesis that the polymers within the aggregates in CN are held together by side chain lamella stacking. Once side chain melts at high temperature, the aggregated polymers start to dissolve leading to a more disordered coiled conformation. On the other hand, the absorption spectra of decane solution always show a well-structured absorption band within the temperature range studied (Figure ). This is consistent with our observation shown in Figure that the micron size agglomerates in decane persist up to 170 °C which is near the boiling point of decane (174 °C). Polymer backbones within those aggregates are held together by strong π interactions to reduce their unfavorable solvophobic interactions with decane, which inhibits conformational change of the backbone even at high temperature.