A new type of bis-PDA, in which two PDAs are linked via an intervening p-phenylene group, is developed. The Bis-PDA-Ph displays exceptional thermochromic reversibility owing to the presence of unique hydrophobic interactions between alkyl chains as well as aryl moieties. The Bis-PDA-Ph has a well-packed structure that causes it to display a clear blue to red colorimetric transition at elevated temperatures. To elucidate the molecular origin of the thermochromic response, a theoretical simulation of the new PDA, the results of which successfully explain the thermochromic reversibility phenomenon, is conducted. Furthermore, Bis-PDA-Ph-embedded polymer fibers are used as a thermochromic sensor material. It displays excellent reversibility between 20-120 degrees C, which is the largest temperature range reported thus far for PDA based sensors. Finally, transient absorption spectroscopy is employed for the first time to analyze the temperature-dependent fluorescence change of the new PDA.