Mesoporous Organosilica Hybrids Consisting of Silica‐Wrapped π–π Stacking Columns

Abstract

Periodic mesoporous organosilica (PMO) materials prepared by surfactant-directed polycondensation of bridged organosilane precursors (R[Si(OR') 3 ] n ; n ! 2, R = organic bridging groups, R' = methyl, ethyl, etc.) are a new class of functional porous hybrid materials. [1][2][3][4][5][6] Organic groups R can be densely embedded within the pore walls without plugging the mesopores. Various organic bridges R ranging from functional p systems to metal complexes are available for tailoring functional frameworks with particular properties, such as tuning of HOMO-LUMO levels, fixation of electroactive organic groups, and formation of reactive and catalytic sites. [7][8][9][10][11][12] One of the most remarkable features of PMOs is the induction of molecular-scale periodicity in the pore wall, which has been realized for PMOs synthesized from dipodal rod-like precursors with rigid p-conjugated aromatic bridges (for example, 1,4-phenylene and 4,4'-biphenylylene) under basic hydrolytic conditions (Figure 1 a, left). [13][14][15][16][17][18][19][20] Molecularscale "crystal-like" ordering of the framework should enable design and control of the optical, electrical, and surface properties of PMOs. However, all of the conventional crystallike PMOs show lamellar structures consisting of alternating organic and silica layers (Figure 1 a, left). [13][14][15][16][17][18][19][20] In this configuration, the distance between neighboring organic bridges is about 0.44 nm, which is much longer than typical face-to-face p-p stacking distances (0.34-0.36 nm); [21,22] therefore, neither strong electronic coupling nor significant electroconductive properties are expected for the pore walls. The lamellar arrangement is thought to be directed by a hydrophobichydrophilic interaction of fully hydrolyzed dipodal precursors ((HO) 3 SiÀRÀSi(OH) 3 ) and subsequent polycondensation; the position and distance of the organic bridges are restricted by the chemical bond length of the siloxane network.Herein we present the first synthesis of a new class of molecularly ordered PMOs with columnar stacking of the bridging organic groups with a face-to-face p-stacking distance of 0.35-0.36 nm (Figure 1 a, right). The new PMOs were synthesized by surfactant-directed polycondensation of newly designed disk-like alkoxysilane precursors with hydrophobic and electroactive perylene bisimide (PBI) [22] cores (Figure 1 b). The key to the formation of this new type of the ordered structure is full utilization of the p-p stacking nature of the hydrophobic PBI moieties rather than the hydrophobic-hydrophilic interaction. As shown in Figure 1 c, the formation of mesostructured hybrids consisting of p-stacked PBI columns and micellar aggregates of a cationic surfactant is promoted under basic hydrolytic conditions through columnar self-assembly of disk-like PBI precursors and electrostatic interaction between the cationic surface of the micelles and the anionic silanolate groups of the columnassembled precursors. The PBI columns are then wrapped and reinforced with a pur...

Periodic Mesoporous Organosilica with Molecular‐Scale Ordering Self‐Assembled by Hydrogen Bonds

“…In addition, stripe patterns with aperiodicity of about 2nmwere partially observed in the TEM images ( Figure S7). This new molecular order was realized through acombination of the cooperative self-assembly of 1 and C 18 TMACl, and H- . Figure 3shows astructural model of the PMO synthesized using 1.T he proper development of H-bonded chains of cyclohexane triamide moieties suggests that the pore walls consist of H-bonded organosilica columns with 2D hexagonal packing.T he diameter of the H-bonded organosilica column is estimated to be about 1.7 nm by molecular modeling,which agrees with the lattice constant (1.65 nm) of the molecularscale 2D hexagonal packing obtained by XRD.C omparing the mesoscale periodicity of the PMO (5-6 nm) with the DFT pore diameter (3.1 nm), the thickness of the pore wall is thought to be 3nm.…”

“…[16] Thef irst example was reported for ab enzene-bridged PMO in 2002, [8] which possessed alternating benzene-silica lamellar structures.A similar "crystal-like" lamellar ordering for pore walls has been found in PMOs prepared from organosilane precursors with various hydrophobic bridging Rgroups,s uch as biphenyl, 1,4-divinylbenzene,n aphthalene,a nd 2,2'-bipyridine. [18] In this study,w ep resent an ovel approach to achieving ac rystal-like arrangement in the pore wall of PMOs.W e reasoned that if an organosilane precursor has H-bonding components within its molecule,anew type of molecularscale ordering can be induced in the pore walls of that PMO. [17] However,s ince the above-mentioned first report in 2002, there have been no studies on other types of crystallike PMOs showing molecular-scale ordering of pore walls except for the lamellar ordering.A lthough we reported electroactive PMOs containing p-stacked columns of perylenebisimide within the pore wall in 2012, regular packing or long-range ordering of the columnar assemblies was not confirmed.…”

Design of Multifunctional Fluorescent Hybrid Materials Based on SiO2 Materials and Core–Shell Fe3O4@SiO2 Nanoparticles for Metal Ion Sensing

“…In 2014, Han and co‐workers developed PMO‐based selective Cu 2+ ‐sensor PMOs‐RhD‐6, which displayed Cu 2+ ‐induced fluorescence enhancement emission with high selectivity and sensitivity (limit of detection = 1.0 × 10 −5 m ) in ethanol‐HEPES (HEPES = 4‐(2‐hydroxyethyl)‐1‐piperazineethanesulfonic acid) (8:2, v:v) aqueous solution at pH 6.8 according to the mechanism of CHEF . Hybrid sensor PMOs‐RhD‐6 showed two absorption bands at 212 and 301 nm, after complex with Cu 2+ ions these bands shifted to 260 and 524 nm due to the charge transfer (CT) transition from the electron‐rich rhodamine p‐conjugated system to the electron‐poor copper ions . In 2013, this research group successfully synthesized hybrid material PMOs‐RhD‐7 for selective Cu 2+ ion sensing purpose where the detection limit toward Cu 2+ ions was calculated to be 6.5 ppb …”

“…[75] Hybrid sensor PMOs-RhD-6 showed two absorption bands at 212 and 301 nm, after complex with Cu 2+ ions these bands shifted to 260 and 524 nm due to the charge transfer (CT) transition from the electron-rich rhodamine p-conjugated system to the electron-poor copper ions. [76] In 2013, this research group successfully synthesized hybrid material PMOs-RhD-7 for selective Cu 2+ ion sensing purpose where the detection limit toward Cu 2+ ions was calculated to be 6.5 ppb. [77] Fibrous silica nanosphere first developed by Polshettiwar et al, known as KCC-1, is the new family of the emerging silica materials with a special fibrous morphology, which possesses several advantages such as high surface area, and high thermal and hydrothermal stabilities.…”

Periodic Mesoporous Organosilica with Molecular‐Scale Ordering Self‐Assembled by Hydrogen Bonds

“…[17] However,s ince the above-mentioned first report in 2002, there have been no studies on other types of crystallike PMOs showing molecular-scale ordering of pore walls except for the lamellar ordering.A lthough we reported electroactive PMOs containing p-stacked columns of perylenebisimide within the pore wall in 2012, regular packing or long-range ordering of the columnar assemblies was not confirmed. [18] In this study,w ep resent an ovel approach to achieving ac rystal-like arrangement in the pore wall of PMOs.W e reasoned that if an organosilane precursor has H-bonding components within its molecule,anew type of molecularscale ordering can be induced in the pore walls of that PMO. Thus,w ed esigned cyclohexane triamide derivative 1 (Figure 1a), because the cyclohexane triamide moiety is known as as trong H-bonding component and has been applied to functional supramolecular materials such as low-molecularweight gelators,t hickeners,a nd stimuli-responsive nanofibers.…”