Insights into the Photophysics and Supramolecular Organization of Congo Red in Solution and the Solid State

Abstract

Steady-state and time-resolved absorption and fluorescence measurements are reported for Congo Red (CR) in aqueous and dimethylsulfoxide (DMSO) solutions. The very low fluorescence quantum yield (≈10 ) for CR in dilute solutions together with the absence of a triplet state indicates that internal conversion is the dominant deactivation route with more than 99.99 % of the quanta loss (attributed to the energy gap law for radiationless transitions). Although no direct evidence for trans-cis photoisomerization was obtained from absorption or fluorescence data, the global analysis of fs-transient absorption data indicates the presence of a photoproduct with a lifetime of ≈170 ps that is suggested to be associated with such a process. Spectral data for more concentrated CR solutions indicate the presence of oblique or twisted J-type aggregates. These results are compared with spectra for CR in the solid state (sodium salt) and intercalated in a layered double hydroxide via a one-step co-precipitation route. Powder XRD and electronic spectral data for the nanohybrid indicate that the CR guest molecules are intercalated as a monolayer consisting of slipped cofacial J-type aggregates.

Open hardware microsecond dispersive transient absorption spectrometer for linear optical response

“…This measurement demonstrates the ability of the instrument to measure 0.15 mOD signals (induced absorption). The shape and form of the TA signals for Congo red are consistent with reported in femtosecond transient absorption spectroscopy [25], while the timescales are far slower due to the polar solvent.…”

One‐Pot Intercalation Strategy for the Encapsulation of a CO‐Releasing Organometallic Molecule in a Layered Double Hydroxide

“…Solvents were dried using standard protocols (THF over Na/benzophenone, CH 2 Cl 2 and hexane over CaH 2 , ethyl acetate over Na 2 SO 4 ), distilled and degassed prior to use. A nitrate-form Zn,Al-LDH (denoted Zn,Al-NO 3 ) with the composition Zn 4 Al 2 (OH) 12 (NO 3 ) 2 •2.5H 2 O was prepared by using the standard method of coprecipitation of the Zn 2+ and Al 3+ hydroxides (initial Zn 2+ /Al 3+ molar ratio in solution = 2) in the presence of nitrate ions at a constant pH of 7.5-8 under nitrogen, followed by aging of the gel at 80°C for 20 h. [42,53] Literature methods were used to prepare [Mo(CO) 3 (η 6 -C 7 H 8 )] [54] and [Mo(CO) 3 (CNCH 2 COOH) 3 ] (ALF795). [45] Physical measurements: Microanalyses for C, H and N were carried out with a Truspec Micro CHNS 630-200-200 elemental analyzer.…”

Intercalation of (η5‐Pentamethylcyclopentadienyl)trioxomolybdenum(VI) in a Layered Double Hydroxide

“…Materials and methods: The chemicals 1,2,3,4,5‐pentamethylcyclopentadiene (94 %, Alfa‐Aesar), sodium amide, hexane (99 %) Mo(CO) 6 , anhydrous tetrahydrofuran (99 %), 70 % TBHP in water, Zn(NO 3 ) 2 · 6H 2 O (Fluka), Al(NO 3 ) 3 · 9H 2 O (Riedel‐de‐Haën), 1 m NaOH, sodium carbonate (José M. Vaz Pereira), cis ‐cyclooctene (95 %, Alfa Aesar), 5.5 m TBHP in decane, α,α,α‐trifluorotoluene (>99 %), diethyl ether (99.8 %), pentane (95 %, Carlo Erba), and undecane (> 99 %) were purchased from Sigma‐Aldrich unless otherwise stated, and used as received. A nitrate‐form Zn,Al LDH (denoted Zn,Al‐NO 3 ) with the composition Zn 4 Al 2 (OH) 12 (NO 3 ) 2 · 2.5H 2 O was prepared by using the standard method of coprecipitation of the Zn 2+ and Al 3+ hydroxides (initial Zn 2+ /Al 3+ molar ratio in solution = 2) in the presence of nitrate ions at constant pH (7.5–8) under nitrogen, followed by aging of the gel at 80 °C for 20 h , . Unless otherwise stated, all preparations and manipulations were carried out using Schlenk techniques under a nitrogen atmosphere.…”