Photophysical Effects between Spirobenzopyran−Methyl methacrylate-Functionalized Colloidal Particles

Abstract

Colloidal particles were derivatized with end-grafted polymethylmethacrylate polymer brushes containing varying concentrations of spirobenzopyran photochromic molecules. The polymers were grown from initiator-functionalized silica particles by an atom-transfer radical polymerization (ATRP). These core-shell colloids formed stable suspensions in toluene with the spirobenzopyran in its closed, nonpolar form. However, UV-induced photoswitching of the photochrome to its open, polar merocyanine isomer caused rapid aggregation. The nature of this colloidal stability transition was examined with respect to the spirobenzopyran content in the polymeric brush and solvent polarity. Turbidimetry, wettability studies, UV-vis spectroscopy, suspension rheology, SEM, and visual inspection were utilized to characterize the system photoswitchability. It was found that the system exhibiting the greatest transition in toluene was the copolymer brush composed of 20% spirobenzopyran and 80% methyl methacrylate.

Light-controlled self-assembly of reversible and irreversible nanoparticle suprastructures

“…are estimated from literature data for chemically similar interfaces (n-alkane/toluene and n-alkane/methanol) noting that alkane/toluene Ͻ Ͻ alkane/MeOH , 12 can be approximated as 12 ϭ x alkane/MeOH , where x is the volume fraction of methanol in solution. Combining expressions for 11 and 12 and substituting numerical values, the interaction energy is then written as E ad ϭ Ϫ(0.045 kcal/mol)N azo Ϫ (3.3 kcal/mol)x.…”

“…For example, nanoscopic components of dimensions significantly smaller than the wavelength of light cannot be efficiently addressed and assembled by using optical confinement techniques [e.g., laser interference (8) and optical trapping (9)], on which virtually all colloidal LISA systems are based. At the same time, LISA based on light-induced interactions between nanoscale components coated with photoswitchable molecules (12,13) has invariably led to disordered precipitates rather than crystalline assemblies. Here, we describe a system that circumvents these limitations, and in which photoisomerization of dithiol molecules bound onto the surfaces of metal nanoparticles (NPs) mediates their LISA into ordered, three-dimensional suprastructures: light-reversible or irreversible crystals (Figs.…”

Functionalized gold nanoparticles: Synthesis, structure and colloid stability

“…Chromophores such as azobenzene or spiropyrene have been attached to oxides or metal particle surfaces as terminal groups [49,52,98,[127][128][129][130][131][132]. Spiropyrene has closed and opened structures, which are switchable upon light irradiation.…”

Light-controlled self-assembly of non-photoresponsive nanoparticles

“…Consequently, the light-directed self-assembly of NPs has been investigated extensively during the past decade, and this has resulted in, for example, photocontrolled catalysis 22 and high-resolution patterning of surfaces with colloids 23 . However, these systems are all based on NPs functionalized chemically with monolayers of light-responsive molecular switches (typically azobenzenes [24][25][26] and spiropyrans (SPs) [27][28][29][30], which not only makes their preparation cumbersome, but can also significantly and adversely affect the performance of the switches because of electronic interactions with the metallic substrates 31,32 . Inspired by recent reports on the magnetic assembly of non-magnetic particles, we envisaged a new methodology to control the assembly of non-photoresponsive NPs with light.…”