Confinement Effect of Micro- and Mesoporous Materials on the Spectroscopy and Dynamics of a Stilbene Derivative Dye

Abstract

Micro- and mesoporous silica-based materials are a class of porous supports that can encapsulate different guest molecules. The formation of these hybrid complexes can be associated with significant alteration of the physico-chemical properties of the guests. Here, we report on a photodynamical study of a push–pull molecule, trans-4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), entrapped within faujasite-type zeolites (HY, NaX, and NaY) and MCM-41 in dichloromethane suspensions. The complex formation gives rise to caged monomers and H- and J-aggregates. Steady-state experiments show that the nanoconfinement provokes net blue shifts of both the absorption and emission spectra, which arise from preferential formation of H-aggregates concomitant with a distortion and/or protonation of the DCM structure. The photodynamics of the hybrid complexes are investigated by nano- to picosecond time-resolved emission experiments. The obtained fluorescence lifetimes are 65–99 ps and 350–400 ps for H- and J-aggregates, respectively, while those of monomers are 2.46–3.87 ns. Evidences for the presence of a charge-transfer (CT) process in trapped DCM molecules (monomers and/or aggregates) are observed. The obtained results are of interest in the interpretation of electron-transfer processes, twisting motions of analogues push–pull systems in confined media and understanding photocatalytic mechanisms using this type of host materials.

Interrogating the Behaviour of a Styryl Dye Interacting with a Mesoscopic 2D-MOF and Its Luminescent Vapochromic Sensing

“…The absorption spectrum of the DCM/Al-ITQ-HB- d composite prepared with a concentration of [DCM] 0 = 5 × 10 −6 M exhibits a broad and structureless band with an intensity maximum at 478 nm ( Figure 1 B). This value is close to the one shown in dichloromethane solutions (466 nm) [ 30 , 40 , 49 , 50 ]. Therefore, we assign this band to the S 0 (π) → S 1 (π*) transition.…”

“…DCM is largely used as a probe of local environment properties. Its photobehavior has been extensively investigated in a variety of solvents [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ] and in presence of confined media such as micelles [ 31 , 32 ], lipid vesicles [ 33 , 34 ], microemulsion [ 35 ], human serum albumin (HSA) [ 36 ], polyvinyl carbazole (PVK) [ 37 ], polypeptide-surfactant aggregate [ 38 ], micro-/mesoporous materials [ 39 , 40 ], and MOFs [ 41 ]. All these investigations demonstrate that DCM experiences a photoinduced intramolecular charge transfer (ICT).…”

“…By increasing the polarity of the medium, the decay times are longer (1.36 ns in MeOH and 2.24 ns in DMSO) and no emission from the S 1 -LE state was detected [ 23 , 25 , 26 , 27 ], indicating that the TICT process becomes faster. In most of the reports on DCM supported on solid surfaces, the LE emission has not been observed because the TICT reaction still remains ultrafast [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ]. However, there are few studies where DCM deactivates from both LE and CT state such as when encapsulated within MCM41 39 and into the pores of a Zr-naphthalene dicarboxylic acid (Zr-NDC) MOF [ 41 ].…”

“…However, there are few studies where DCM deactivates from both LE and CT state such as when encapsulated within MCM41 39 and into the pores of a Zr-naphthalene dicarboxylic acid (Zr-NDC) MOF [ 41 ]. In addition to the forementioned, the interaction of high concentration of DCM with different silica-based materials, such as faujasite-type zeolites (HY, NaX, and NaY) and MCM41, can lead to the formation of aggregated species [ 40 ]. For instance, it has been shown that H- and J-aggregates relax with lifetimes of 65–99 ps and 350–400 ps, respectively, while the monomers decay in the range of 2.44–3.9 ns [ 40 ].…”

“…In addition to the forementioned, the interaction of high concentration of DCM with different silica-based materials, such as faujasite-type zeolites (HY, NaX, and NaY) and MCM41, can lead to the formation of aggregated species [ 40 ]. For instance, it has been shown that H- and J-aggregates relax with lifetimes of 65–99 ps and 350–400 ps, respectively, while the monomers decay in the range of 2.44–3.9 ns [ 40 ]. Although the photodynamics of DCM molecules in solid 3D-porous materials is relatively well understood, its interaction with 2D-MOFs still remains unexplored.…”