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

Maria Di Nunzio,Abderrazzak Douhal,Ganchimeg Perenlei

doi:10.3390/ijms20061316

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.

Highlights

Trapping organic molecules in the interior of meso/nanosized hybrid materials have been fascinating the scientific community since the 1980s for the possibility to form composites of great interest in advanced chemical and biological applications like catalysis, photonics, and drug delivery [1]
We propose the existence of DCM monomers along with H- and J-aggregates in the cases of NaX, NaY, and MCM-41 compounds, being the absorption spectra of these complexes very similar to the DCM@HY one
The Stokes shift values observed for the DCM@zeolite complexes (∆vmabasx−em= 5415, 5590, and 5850 cm−1 for DCM@HY, DCM@NaX, and DCM@NaY, respectively) and for DCM@MCM-41 (∆vmabasx−em= 4850 cm−1) are higher than that observed in dichloromethane solution (∆vmabasx−em= 4510 cm−1), indicating that excited-state CT reactions may occur for trapped DCM molecules

Summary

Introduction

Trapping organic molecules in the interior of meso/nanosized hybrid materials have been fascinating the scientific community since the 1980s for the possibility to form composites of great interest in advanced chemical and biological applications like catalysis, photonics, and drug delivery [1]. The Stokes shift values observed for the DCM@zeolite complexes (∆vmabasx−em= 5415, 5590, and 5850 cm−1 for DCM@HY, DCM@NaX, and DCM@NaY, respectively) and for DCM@MCM-41 (∆vmabasx−em= 4850 cm−1) are higher than that observed in dichloromethane solution (∆vmabasx−em= 4510 cm−1), indicating that excited-state CT reactions may occur for trapped DCM molecules (monomers and/or aggregates). The DCM confinement within HY, NaX, and NaY zeolites leads to a substantial decrease in the global fluorescence intensity via additional non-radiative decay channels like self-quenching processes This has been observed for several organic dye guests within such kind of host materials [1]. FFiigguurree 66 ddiissppllaayyss tthhee eemmiissssiioonn ddeeccaayyss ooff DDCCMM iinn ddiicchhlloorroommeetthhaannee ssoolluuttiioonn aanndd iinn ccoonnttaacctt wwiitthh MMCCMM--4411 ((iinniittiiaallddyyeeccoonncceenntrtraatitoionn: :11××101−40M−4) Min)diinchdliocrholmoreotmhaentheasnuespseunspsieonnseioxnciteixncgitaint g37a1tn3m71annmd oanbsdeorvbisnegrvaitn4g5a0ta4n5d0 6a0n0dn6m00. Noormrmaalilzizeded(t(otoththeemmaxaximimuummoof finintetnensistiyty) )mmagagici-ca-nanggleleememisissisoionnddeceacyasysofofDDCCMM@@MMCCMM-4-411 cocommppoosistiete(i(niintiitailadl ydeyecocnocnecnetnrtartaiotino:n1: 1××101−0−44 MM))ininddicihchlolororommeeththaanneesususpspeennsisoionnssananddcocmompparairsiosnon wwitihthththeefrfereeeddyyeeininddiicchhlloorroommeetthhaannee ssoolluuttiioonn eexxcciittiinngg aatt337711nnmmaannddoobbseservrvininggatat(1()14) 54050nmnmanadnd(2) (26)0600n0mn.mT.hTehoebsoebrsveartvioantiownawvealvenelgetnhgftohr ftohretfhreeefrdeyeedisy6e0i0s n60m0.nTmhe. sTohliedsloinliedslainreesfraorme ftrhoembethstembueslttimeuxlptio-nexepnotinael nfittisaltofittshetoetxhpeereixmpeenritmalednatatal .dIaRtFa.isIR~F7i0s p~s7.0 ps

Materials and Methods

Findings

Conclusions