Alternative external stimuli, such

Alternative external stimuli, such as heat and light, induce color
and visible absorption spectrum changes in photochromic molecules
[1–3]. Spiropyrans undergo a photoinduced ring opening from a
nonpolar, colorless spiropyran (SP-form) to a polar, colored merocyanine
(MC-form) [4]. The use of spiropyrans in ionic and pH sensors
[5,6] to indicate ionic concentration has been investigated because of
their high sensitivity to the surrounding environment. Recent studies
have used spiropyrans to achieve switchable photoluminescence (PL)
by implementing spiropyran-functionalized nanostructures [7–12]. In
the current study, the fluorescence observed in organic–organic or
organic–inorganic hybrids was strongly quenched by the colored MCform
of spiropyran because of a strong absorption band located in the
range of 550–660 nm. Emissions from the hybrids could be switched
on and off by using alternating UV and visible light irradiation.
Porous silicon (PS) is well known for its strong PL visible at
room temperature, resulting from the quantum confinement of
quantum-size crystalline structures fabricated using electrochemically
etched silicon [13]. PL intensity and peak wavelength changes