Time-dependent Density Functional Theory-polarized Continuum Model Research Articles

Functional group induced excited state intramolecular proton transfer process in 4-amino-2-methylsulfanyl-pyrimidine-5-carboxylic acid ethyl ester: a combined spectroscopic and density functional theory study

The molecule methyl-2-aminonicotinate (2-MAN) does not exhibit excited state intramolecular proton transfer (ESIPT), but its derivative 4-amino-2-methylsulfanyl-pyrimidine-5-carboxylic acid ethyl ester (AMPCE), widely used in the preparation of pyrimidopyrimidines as a protein kinase inhibitor, does exhibit ESIPT. Increasing acidic and basic character at the proton donor and proton acceptor sites by adding functional groups is found to be responsible for the large Stokes shifted ESIPT emission (Δν = 12,706 cm(-1)) in AMPCE. The photophysics of AMPCE have been explored on the basis of steady state and time resolved spectral measurements, quantum yield calculation with variation of polarity, as well as hydrogen bonding ability of solvents. Experimental findings have been correlated with the calculated structure and potential energy surfaces based on the intramolecular proton transfer model obtained by density functional theory (DFT). Properties based on the calculated excited state surfaces generated in vacuo and methanol solvent using time dependent density functional theory (TDDFT) and time dependent density functional theory polarized continuum model (TDDFT-PCM), respectively, show good agreement with the experimental findings. HOMO and LUMO diagrams also support the favorable ESIPT process in the first excited state potential energy surface.

Excited State Charge Transfer reaction with dual emission from 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile: Spectral measurement and theoretical density functional theory calculation

The excited state intramolecular charge transfer process in donor–chromophore–acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been investigated by steady state absorption and emission spectroscopy in combination with Density Functional Theory (DFT) calculations. This flexible donor acceptor molecule DMAPPDN shows dual fluorescence corresponding to emission from locally excited and charge transfer state in polar solvent. Large solvatochromic emission shift, effect of variation of pH and HOMO–LUMO molecular orbital pictures support excited state intramolecular charge transfer process. The experimental findings have been correlated with the calculated structure and potential energy surfaces based on the Twisted Intramolecular Charge Transfer (TICT) model obtained at DFT level using B3LYP functional and 6-31+G( d, p) basis set. The theoretical potential energy surfaces for the excited states have been generated in vacuo and acetonitrile solvent using Time Dependent Density Functional Theory (TDDFT) and Time Dependent Density Functional Theory Polarized Continuum Model (TDDFT-PCM) method, respectively. All the theoretical results show well agreement with the experimental observations.

Substituent and Solvent Effects on Electronic Structure and Spectral Property of ReCl(CO)3(N∧N) (N∧N = Glyoxime): DFT and TDDFT Theoretical Studies

The ground- and excited-state structures of five Re(I) halide glyoxime complexes ReCl(CO)(3)(N(∧)N) (N(∧)N = glyoxime (DHG 1), dimethylglyoxime (DMG 2), cyclohexane dione glyoxime (CHDG 3), dibromoglyoxime (DBG 4), and dimethylformylgloxime (DMFG 5)) have been studied with density functional theory (DFT) and configuration interaction with single excitations (CIS) methods. Time-dependent density functional theory/polarized continuum model (TDDFT/PCM) was carried out to predict the absorption and emission spectra in different media. The effect of substituent and solvent has been researched. It is found that electron-donating groups increase the lowest unoccupied molecular orbital (LUMO) energy resulting in the increased highest occupied molecular orbital (HOMO)-LUMO energy gap. The change leads to their absorption spectra blue shifts in the order 1 > 2 > 3, which arises from the HOMO-1 → LUMO. Just the opposite, electron-withdrawing groups lead to the spectra red shifts (5 > 4 > 1) because of the decreased HOMO-LUMO energy gap. The reorganization energy (λ) calculations show that the relatively balanceable charges transfer abilities of 2 will result in the higher efficiency of organic light emitting devices (OLEDs). In addition, both the absorption and the emission spectra display red shifts in different extents with the decrease of solvent polarity.

Evidence for excited state intramolecular charge transfer reaction in donor–acceptor molecule 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester: Experimental and quantum chemical approach

Intramolecular charge transfer (ICT) reaction has been investigated in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME) using spectroscopic techniques. The molecule DPDAME shows local emission in non-polar solvent and dual emission in polar solvents. Solvatochromic effects on the Stokes shifted emission band clearly demonstrate the charge transfer character of the excited state. Quantum chemical calculations have been performed at Hartree–Fock (HF) and density functional theoretical (DFT) levels to correlate the experimental findings. Potential energy curves (PECs) for the ICT reaction have been evaluated along the donor twist angle at DFT and time dependent density functional theory (TDDFT) levels for the ground and excited states, respectively, using B3LYP hybrid functional and 6-31G ⁎ ⁎ basis set. The solvent effects on the spectral properties have been explored theoretically at the same level with time dependent density functional theory-polarized continuum model (TDDFT-PCM) and the theoretical results are found to well substantiate the solvent polarity dependent Stokes shifted emission of DPDAME. Huge enhancement of dipole moment (Δ μ=16.42 D) of the molecule following photoexcitation dictates the highly polar character of the excited state. Although elucidation of PECs does not exactly predict the operation of ICT according to twisted intramolecular charge transfer (TICT) model in DPDAME, lowering of vertical transition energy as a function of the donor twist coordinate scripts the occurrence of red shifted emission as observed experimentally.

Spectroscopic and theoretical evidence for the photoinduced twisted intramolecular charge transfer state formation in N, N-dimethylaminonaphthyl-(acrylo)-nitrile

The phenomenon of excited state twisted intramolecular charge transfer (TICT) process in N, N-dimethylaminonaphthyl-(acrylo)-nitrile (DMANAN) has been reported on the basis of steady-state absorption and fluorescence spectroscopy in combination with quantum chemical calculations. The absorption and fluorescence characteristics of DMANAN in solvents of different polarity reveal the presence of a single species in the ground state which forms the intramolecular charge transfer state upon photoexcitation. The observed dual fluorescence is assigned to a high-energy emission from the locally excited or the Franck–Condon state and the red-shifted emission from the charge transfer (CT) state. In polar protic solvents, hydrogen-bonding interaction on CT emission has been established from the linear dependency of the position of the low-energy emission maxima on hydrogen-bonding parameter ( α). The experimental findings have been correlated with the theoretical results based on TICT model obtained at density functional theory (DFT) level. The theoretical potential energy surface for the first excited state along both the donor and acceptor twist coordinates in the gas phase obtained by time dependent density functional theory (TDDFT) method and in polar solvent by time dependent density functional theory-polarized continuum model (TDDFT-PCM) method predicts well the experimental spectral properties.

Spectroscopic study of excited state intramolecular charge transfer in ethyl ester of N, N′-Dimethylaminonaphthyl-(acrylic)-acid

In this work, we have studied the twisted intramolecular charge transfer process in ethyl ester of N, N′-Dimethylaminonaphthyl-(acrylic)-acid (EDMANA) using absorption and emission spectroscopy. Single conformer of EDMANA present in the ground state gives rise to local and charge transfer emission in different solvents. Solvatochromic effect on the Stokes shifted emission band clearly indicates the charge transfer character of the emitting singlet excited state. Considering twisted intramolecular charge transfer model, the ground and excited state properties of EDMANA have been evaluated along the donor and acceptor twisting coordinates separately using density functional theory (DFT) and time dependent density functional theory (TDDFT), respectively, with B3LYP functional and 6-31G basis set. The effect of solvent on the spectral properties has been explored theoretically at the same level with time dependent density functional theory-polarized continuum model (TDDFT-PCM) and the theoretical results support the solvent polarity dependent Stokes shifted emission of EDMANA molecule.

Photoinduced Intramolecular Charge Transfer Reaction in (E)-3-(4-Methylamino-phenyl)-acrylic Acid Methyl Ester: A Fluorescence Study in Combination with TDDFT Calculation

A donor-acceptor substituted aromatic system (E)-3-(4-Methylamino-phenyl)-acrylic acid methyl ester (MAPAME) has been synthesized, and its photophysical behavior obtained spectroscopically has been compared with the theoretical results. The observed dual fluorescence from MAPAME has been assigned to emission from locally excited and twisted intramolecular charge transfer states. The donor and acceptor angular dependency on the ground and excited states potential energy surfaces have been calculated both in vacuo and in acetonitrile solvent using time dependent density functional theory (TDDFT) and TDDFT polarized continuum model (TDDFT-PCM), respectively. Calculation predicts that a stabilized twisted excited state is responsible for red shifted charge transfer emission.

Photophysical properties of trans-3-(4-monomethylamino-phenyl)-acrylonitrile: Evidence of twisted intramolecular charge transfer (TICT) process

A donor acceptor substituted aromatic system trans-3-(4-monomethylamino-phenyl)-acrylonitrile (MMAPA) has been synthesized and its photophysical behavior has been investigated in the solvent of different polarity by steady state absorption and emission, time-resolved emission and quantum chemical calculations. The observed dual fluorescence of MMAPA in polar aprotic solvents has been assigned to emission from the locally excited and twisted intramolecular charge transfer states. The low-energy emission in protic solvent is attributed to the hydrogen-bonded complex. Potential energy surfaces for the ground and excited states along the donor (–NHMe group) and acceptor (acrylonitrile group) twist coordinates have been calculated by time-dependent density functional theory (TDDFT) and time-dependent density functional theory-polarized continuum model (TDDFT-PCM) in the gas phase and in acetonitrile solvent, respectively. Calculations predict that the stabilized excited state along the twist coordinate is responsible for the solvent dependent red shifted charge transfer emission. It is found that the twisting along the donor site is energetically favorable compared to that of the acceptor site. The canonical crossing of the excited states for the twisting of the donor group and localized nitrogen lone pair orbital of –NHMe group at the perpendicular configuration with respect to p-orbitals of benzene ring support TICT model for photo-induced charge transfer reaction in MMAPA molecule.