Polythiophene and its derivatives (PTs) are a class of conjugated polymers, and their electronic, optical, and thermodynamic properties in the bulk solid state have been studied extensively because of their high potential for applications in electronic and optoelectronic devices, such as field-effect transistors (FETs), [1,2] light-emitting diodes (LEDs), [3,4] and solar cells. [5,6] It is well-known that their spectroscopic properties are closely related to coil-like, planar, and distorted conformations of the polymer chain. [7][8][9] In the coil-like conformation, twisted adjacent thiophene rings make the conjugation length short and its distribution broad, resulting in blue-shifted and structureless absorption and fluorescence spectra, as compared to the planar conformation, where the thiophene rings are coplanar and the rotating motion is highly limited, that is, making the conjugation length longer and its distribution narrow. The distorted conformation lies between the flexible coil-like and rigid planar conformations. The difference in conformations also affects their thermodynamics. Distorted polymers easily change their conformation to coil-like, which is accompanied by a color change, as the temperature is elevated (thermochromism), whereas a planar polymer needs a relatively high temperature to induce the change, due to its stiffness. [10][11][12][13] Thus, the spectroscopic and thermodynamic properties of PTs provide information on the structure at a molecular level. By utilizing this notable feature, we have succeeded in demonstrating that a difference in polymer conformations and their spatial arrangements evolves into a difference in the nanometer-scaled surface morphology in poly(3-[2-(N-dodecylcarbamoyloxy)ethyl]-thiophene-2,5-diyl), P3DDUT, films (see Figure 1 (a) for the chemical structure). [14,15] Near-field fluorescence microspectroscopy has revealed that fluorescence spectra at protruding domains were slightly blueshifted compared with flat areas, and a further blue-shift could be induced more appreciably by a long excitation time. We have concluded that major polymers take a disordered phase in the protruding domain, in which there are some distortions in the main chain (decreasing the conjugation length) and interchain interactions are rather weak, whereas a planar (ordered) conformation giving a longer conjugation is favored in the flat area.[14] Moreover, we have demonstrated that the P3DDUT films show a nanometer surface protrusion accompanying the blue-shift in the fluorescence spectrum upon nearfield excitation: This phenomenon is attributable to a photothermally-induced conformational change, such as a planar-tocoil transition.[15] Thus, we have made it clear that P3DDUT polymer structures at the molecular level are closely related, not only to spectroscopic and thermodynamic properties, but also to nanometer-scaled surface morphology.Nanoparticles are attractive nanomaterials from both fundamental and technological viewpoints, since they exhibit unique physical and chemical propert...