Resonance Raman Investigation of the Short-Time Photodissociation Dynamics of the Charge-Transfer Absorption of the I2−Benzene Complex in Benzene Solution

Quinoid-Thiophene-Based Covalent Organic Polymers for High Iodine Uptake: When Rational Chemical Design Counterbalances the Low Surface Area and Pore Volume

A novel 2D covalent organic polymer (COP), based on conjugated quinoid-oligothiophene (QOT) and tris(aminophenyl) benzene (TAPB) moieties, is designed and synthesized (TAPB-QOT COP). Some DFT calculations are made to clarify the equilibrium between different QOT isomers and how they could affect the COP formation. Once synthetized, the polymer has been thoroughly characterized by spectroscopic (i.e., Raman, UV-vis), SSNMR and surface (e.g., SEM, BET) techniques, showing a modest surface area (113 m² g^-1) and micropore volume (0.014 cm³ g^-1 with an averaged pore size of 5.6-8 Å). Notwithstanding this, TAPB-QOT COP shows a remarkably high iodine (I₂) uptake capacity (464 %wt) comparable to or even higher than state-of-the-art porous organic polymers (POPs). These auspicious values are due to the thoughtful design of the polymer with embedded sulfur sites and a conjugated scaffold with the ability to counterbalance the relatively low pore volumes. Indeed, both morphological and Raman data, supported by computational analyses, prove the very high affinity between the S atom in our COP and the I₂. As a result, TAPB-QOT COP shows the highest volumetric I₂ uptake (i.e., the amount of I₂ uptaken per volume unit) up to 331 g cm^-3 coupled with a remarkably high reversibility (>80% after five cycles).

UV and Resonance Raman Spectroscopic and Theoretical Studies on the Solvent-Dependent Ground and Excited-State Thione → Thiol Tautomerization of 4,6-Dimethyl-2-mercaptopyrimidine (DMMP)

The vibrational spectra of 4,6-dimethyl-2-mercaptopyrimidine (DMMP) in acetonitrile, methanol, and water were assigned by resonance Raman spectroscopy through a combination of Fourier-transform infrared spectroscopy (FT-IR), FT-Raman UV-vis spectroscopy, and density functional theoretical (DFT) calculations. The FT-Raman spectra show that the neat solid DMMP is formed as a dimer due to intermolecular hydrogen bonding. In methanol and water, however, the majority of the Raman spectra were assigned to the vibrational modes of DMMP(solvent) _n ( n = 1-4) clusters containing NH···O hydrogen bonds. The intermolecular NH···O hydrogen bond interactions, which are key constituents of the stable DMMP thione structure, revealed significant structural differences in acetonitrile, methanol, and water. In addition, UV-induced hydrogen transfer isomeric reactions between the thione and thiol forms of DMMP were detected in water and acetonitrile. DFT calculations indicate that the observed thione → thiol tautomerization should occur easily in lower excited states in acetonitrile and water.

Ultrasonic, spectrophotometric and theoretical studies of sigma and PI interactions of iodine with substituted benzene

The acoustical method shows the ability to study the structure, energetics and spectroscopic aspects of charge transfer complexes of three different benzenoid compounds with iodine and is supported by the UV-Visible and DFT methods.

Resonance Raman and density functional study of the excited state structural dynamics of 3-amino-2-cyclohexen-1-one in water and acetonitrile solvents

FT-Raman and/or FT-IR spectra of 3-amino-2-cyclohexen-1-one (ACyO) in solid state and/or in solvents of water and acetonitrile were obtained. Density functional theory calculations were done to help elucidate the vibrational band assignments. The A-band resonance Raman spectra of ACyO were acquired in water and acetonitrile solvents to examine the excited state structural dynamics and the state-mixing or curve-crossing tuned by solvents. A preliminary resonance Raman intensity analysis using the time-dependent wave-packet theory and simple model was done for ACyO in acetonitrile solvent. Resonance Raman spectroscopic probing of the excited state curve-crossing or state-mixing was proposed.

Resonance Raman spectroscopic and theoretical investigation of the excited state proton transfer reaction dynamics of 2-thiopyridone

The resonance Raman spectra were obtained for both 2-thiopyridone (2TP) and its proton-transfer tautomer 2-mercaptopyridine (2MP) in water solution. Density functional theory (DFT) calculations were carried out to help elucidate their ultraviolet electronic transitions and vibrational assignments of the resonance Raman spectra associated with their B-band absorptions. The nanosecond time-resolved resonance Raman spectroscopic experiment was carried out to further confirm the assignment that the transient species was the ground state 2MP. The different short-time structural dynamics were examined for both 2TP and 2MP in terms of their resonance Raman intensity patterns. The transition barriers between 2TP and 2MP for S(0), T(1), and S(1) states are determined by using (U)B3LYP-TD and CASSCF level of theory computations, respectively. The excited state proton transfer (ESPT) reaction mechanism is proposed and briefly discussed.