Two model compounds, 1,3-bis(9,9-dihexylfluoren-2-yl)azulene (M1), and 1,3-bis[7-(9,9,9′,9′-tetrahexyl-2,2′-bifluoren-7-yl)azulene (M2), and polymers, poly[2,7-(9,9-dialkylfluorenyl)-alt-(1′,3′-azulenyl)] (P1−P4) and poly{[1,3-bis(9′,9′-dihexylfluoren-2′-yl)azulenyl]-alt-[2′′,7′′-(9′′,9′′-dialkylfluorenyl]} (P5, P6) were synthesized by reacting 1,3-dibromoazulene or 1,3-bis(7-bromo-9,9-dihexylfluoren-2-yl)azulene with a suitable 9,9-dialkylflourenyl-2-borate or 2,7-diborate via Suzuki cross-coupling reactions. The thermal and optical properties of the polymers were characterized by thermogravimetric analysis, differential scanning calorimetry, and UV−vis and fluorescence spectroscopy. M1, M2, and P1−P6 are nonfluorescent in the neutral state in different organic solvents. However, M1, M2, P5, and P6 become fluorescent upon the addition of trifluoroacetic acid in THF, with relative quantum efficiencies of 0.004−0.06. The “switching on” of the fluorescence for the azulene−fluorene copolymers and model compo...