Solvatochromic Study of the Microenvironment of Surface-Bound Spiropyrans

Spiropyrans are a group of organic molecules that undergo a reversible photoinduced transformation (i.e., photochromism) from a colorless, nonplanar spiropyran form to a colored, planar merocyanine form. Photochromism is accompanied by a large change in the structure and in the dipole moment. These changes suggest that such molecules might be useful in light-controlled, “smart surface” applications. This study examines the effect of the microenvironment near the surface-bound spiropyran on its photochemistry. The surfaces were designed to exhibit a mixture of hydrophobic and hydrophilic components by using a mixed silane chemistry on a glass substrate, and the spiropyran was covalently bound to the surface via amide linkages. The solvatochromic behavior of spiropyran derivatives was studied in solution using UV−vis absorption spectroscopy and fluorescence spectroscopy for comparison with the surface-bound species. Spiropyrans in solution and on the surface both exhibited negative solvatochromism. Correlat...