Experimental investigation by UV–VIS and IR spectroscopy to reveal electronic and vibrational properties of pyrrole-2-carboxyldehyde: A theoretical approach

Effects of hydrogen bonding between pyrrole-2-carboxaldehyde and nearest polar and nonpolar environment

The present paper represents dominant effects of hydrogen bonding on the existence of different molecular aggregates in one of the heterocyclic pyrrole system: pyrrole-2-carboxaldehyde (PCL). Theoretical and experimental Raman spectral evidence verifies the existence of different molecular aggregates like dimeric, monomeric, hydrated complex states in PCL. Atoms in molecules (AIMs) analysis and fluorescence decay profile provide a strong signature of intermolecular hydrogen bonding (I_erHB) as the possible reason for the existence of cis form of dimeric (X) molecular aggregates. The high remnant polarization of 3.13μCcm^-2 and smaller dielectric loss in solid form of PCL arise due to in X by ordering of dipoles as a result of I_erHB. A remarkable high ferroelectric response in solid phase makes PCL a desirable candidate to be used as raw material for energy storage devices. For solution phase, in presence of external hydroxylic environment, PCL reacts with external water molecules through weak I_erHB and creates different hydrated PCL/(H₂O)_n complexes by creating water bridge with number of water molecules from 1 to n. An increasing number of water molecules helps to form stronger hydrated complex by separation of charges by lowering the transferring energy barrier.

Photoenolization via excited state double proton transfer induces "turn on" fluorescence in diformyl diaryl dipyrromethane

A light triggered enolization in diformyl diaryl dipyrromethane by excited state dual proton transfer (ESDPT) induces "turn on" fluorescence. The role of diaryl and diformyl groups in the enolization process was confirmed by photophysical and theoretical studies.

FT-IR, Laser-Raman spectra and quantum chemical calculations of methyl 4-(trifluoromethyl)-1H-pyrrole-3-carboxylate-A DFT approach

In this study the experimental and theoretical vibrational frequencies of a newly synthesized anti-tumor and anti-inflammatory agent namely, methyl 4-(trifluoromethyl)-1H-pyrrole-3-carboxylate have been investigated. The experimental FT-IR (4000-400cm(-1)) and Laser-Raman spectra (4000-100cm(-1)) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths, bond angles and torsion angles) have been calculated using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr and DFT/M06-2X: highly parameterized, empirical exchange correlation function) with 6-311++G(d,p) basis set by Gaussian 03 software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data and results in the literature. In addition, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy and the other related molecular energy values of the compound have been investigated using the same theoretical calculations.

Excited state behavior of pyrrole 2-carboxyldehyde: theoretical and experimental study

Photophysical and photochemical dynamics of excited state proton transfer reaction have been reported for Pyrrole 2-carboxyldehyde (PCL). Experimental and theoretical observations yield all possible signatures of intramolecular and intermolecular proton transfer in an excited state. Dual emission (~325 nm, ~375 nm) on photo excitation indicates the existence of more than one species in an excited state. Computed reaction pathway and two-dimensional potential energy profile in the ground state reveals a single minimum corresponding to normal form (E). Dual minima in excited state energy profile shows the existence of two species, one normal and other zwitterionic (Z*) species. A large Stokes shifted emission at ~375 nm in hydrocarbon medium reveals the existence of zwitterionic species due to Excited state intramolecular proton transfer (ESI(ra)PT). Excited State Intermolecular proton transfer (ESI(er)PT) is observed in a hydroxylic environment around 430-490 nm. pH variation in hydroxylic medium suggests the formation of anion (A((-))) from Z*.

White light generation by carbonyl based indole derivatives due to proton transfer: an efficient fluorescence sensor

The motivation of the present work is to understand the optical, chemical, and electrical aspects of the proton transfer mechanism of indole (I) and some carbonyl based indole derivatives: indole-3-carboxaldehyde (I3C) and indole-7-carboxaldehyde (I7C) for both powder form and their liquid solution. Structural information for indole derivatives (isolated molecule and in solution) is obtained with density functional theory (DFT) and time dependent DFT (TD-DFT) methods. Calculated transition energies are used to generate UV-vis, FTIR, Raman, and NMR spectra which are later verified with the experimental spectra. The occurrence of different conformers [cis (N(c)), trans (N(t)), and zwitterion (Z*)] have been interpreted by Mulliken charge, natural bond orbital (NBO) analysis, and polarization versus electric field (P-E loop) studies. (1)H and (13)C NMR and molecular vibrational frequencies of the fundamental modes established the stability of Nc due to the presence of intramolecular hydrogen bonding (IHB) in the ground state (S0). Computed/experimental UV-vis absorption/emission studies reveal the creation of new species: zwitterion (Z*) and anion (A*) in the excited state (S1) due to excited state intramolecular and intermolecular proton transfer (ESI(ra)PT and ESI(er)PT). Increased electrical conductivity (σ(ac)) with temperature and increased ferroelectric polarization at higher field verifies proton conduction in I7C.