Photochemistry and Photophysics in Silica-Based Materials: Ultrafast and Single Molecule Spectroscopy Observation

Abstract

Silica-based materials (SBMs) are widely used in catalysis, photonics, and drug delivery. Their pores and cavities act as hosts of diverse guests ranging from classical dyes to drugs and quantum dots, allowing changes in the photochemical behavior of the confined guests. The heterogeneity of the guest populations as well as the confinement provided by these hosts affect the behavior of the formed hybrid materials. As a consequence, the observed reaction dynamics becomes significantly different and complex. Studying their photobehavior requires advanced laser-based spectroscopy and microscopy techniques as well as computational methods. Thanks to the development of ultrafast (spectroscopy and imaging) tools, we are witnessing an increasing interest of the scientific community to explore the intimate photobehavior of these composites. Here, we review the recent theoretical and ultrafast experimental studies of their photodynamics and discuss the results in comparison to those in homogeneous media. The discussion of the confined dynamics includes solvation and intra- and intermolecular proton-, electron-, and energy transfer events of the guest within the SBMs. Several examples of applications in photocatalysis, (photo)sensors, photonics, photovoltaics, and drug delivery demonstrate the vast potential of the SBMs in modern science and technology.

Supramolecular Organization in Confined Nanospaces

“…[793] As also evidenced by the presented examples, the information obtained by molecular simulation has already contributed to design host-guest materials with improved optical properties. [28] The integration between experiment and theory is particularly advanced in clathrate hydrate research, [315] favoring progress also in the emerging field of confined hydrates. [346,794] Calculations have become important to characterize disordered systems such as zeolite-metal clusters compounds, and the progress of multiscale modeling [795] has helped to broaden length and time scales in simulation.…”

“…Most of the herein discussed composites are functional in spite of disorder: for example, the electronic transition dipole moments of the dyes incorporated in zeolite L (Figure b) are approximately aligned, ensuring thus an extremely high speed for exciton transport ,. Technically, this is good enough for use in solar energy concentrators, sensors or solar cells . Of course, there is still room for improvement, which requires a thorough, atomistic‐level characterization of the material.…”

“…[16,17] Nanoscale confinement has long been used as a way to enhance or modify chemical reactivity, as documented in several reviews on catalysis, [18][19][20][21][22] photochemistry, [23][24][25][26] and charge-transfer processes. [27,28] Equally important are situations where no covalent bonds are broken or formed, and the porous matrix is used essentially as an organizing medium. In such host-guest or inclusion composites, the guest species are bound inside the cavities or channels of the host by noncovalent forces such as hydrogen bonding, halogen bonding, electrostatics and van der Waals interactions.…”

“…[36,40] Technically, this is good enough for use in solar energy concentrators, sensors or solar cells. [28] Of course, there is still room for improvement, which requires a thorough, atomistic-level characterization of the material. Indeed, despite great progresses in experimental techniques (sketched in Section 2), important details remain very difficult to capture, especially when fine movements of molecules or groups of atoms are the main characters of the play.…”

Easily Accessible Schiff Base ESIPT Molecules with Tunable Solid State Fluorescence: Mechanofluorochromism and Highly Selective Co2+ Fluorescence Sensing

“…[9][10][11][12][13][14][15] On the other hand, excited state intramolecular proton transfer (ESIPT) mechanism lead to strong fluorescence in the solid state from planar π-conjugated molecules. [16][17][18][19][20][21][22] The photoinduced ESIPT from enol (E*) to keto (K*) tautomer, proton migration within an intramolecular hydrogen bonding site, exhibited strong emission with large Stokes shift. [16][17][18][19][20][21][22][23][24][25][26][27] Further, the distinct four-level laser scheme of enol-keto photocycle (EÀ E*À K*À KÀ E) have been made use for developing laser dyes.…”