Two simple, structurally related photochromic Schiff bases, salicylideneaniline (SA) and salicylaldehyde azine (SAA) were studied in femto– and picosecond time domains. In both systems an ultrafast excited state intramolecular proton transfer (ESIPT) reaction was stated with the characteristic time below 50 fs. For SA this result is in contrast to the recent data published by Mitra and Tamai (S. Mitra and N. Tamai, Chem. Phys. Lett., 1998, 282, 391; S. Mitra and N. Tamai, Chem. Phys., 1999, 246, 463; S. Mitra and N. Tamai, Phys. Chem. Chem. Phys., 2003, 5, 4647), reporting on the corresponding time as long as 200–300 fs. The kinetics of decay of keto-tautomers in S₁ states was followed by the transient absorption (410 nm and 470 nm for SA and SAA, respectively) and stimulated emission bands. About 10–30% of excited molecules give birth to the long-lived ground states of photochromic forms.

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.

A photochromic symmetric Schiff base, N,N′-bis(salicylidene)-p-phenylenediamine, is proposed as a probe for the study of solvent dependent enol-keto tautomerism in the ground and excited states. The ground state equilibrium between the enol-keto tautomers is found to depend mainly not on polarity but on the proton donating ability of the solvent. Upon selective excitation of each of these tautomers, the same excited state of a keto tautomer is created: in enol, after the ultrafast excited state intramolecular proton transfer (ESIPT), reaction, and in keto tautomer, directly. Then some part (<30%) of excited molecules are transferred to the photochromic form in its ground state. The evidence of another ultrafast deactivation channel in the excited enol tautomer competing with ESIPT has been found. The solvent does not influence the ESIPT dynamics nor the efficiency of the creation of the photochrome.