Calculations Of Optimized Geometries Research Articles

Effect of the π-bridge structure on the intramolecular charge transfer of push–pull 2-phenylthiophene and 2-(furan-2-yl)pyridine derivatives

Effect of the bridge structure on the photophysical properties of D-π-A of structurally similar 2,5-diphenylthiophene (cpd. I) and 2-(5-phenylfuran-2-yl)pyridine (cpd. 2) derivatives having the same electron donating and electron withdrawing groups were studied in different solvents. Solvent effect on the absorption and fluorescence emission spectra as well as their excited state decay were studied in detail. Introduction of 2,5-diphenylthiophene and 2-(5-phenylfuran-2-yl)pyridine between methoxy and carbonitrile groups lead to a shift of about 20 nm in both the absorption and fluorescence emission maxima of the former. Stokes shift of about 90 nm was observed for both compounds in protic solvents and polar aprotic solvents and decreases as the solvent polarity decreases. The solvatochromism in the fluorescence emission spectra was higher than the observed in absorption spectra, indicating higher dipole moment in the excited state than in the ground state for both compounds. DFT and TD-DFT optimized geometry calculations show that (I) is planar in the excited state while (II) is planar in both the ground and excited states reflecting the importance of the bridge structure on the geometry in the ground and excited states. Theoretical calculations of the dipole moment change from the ground to the excited states were consistent with the values obtained from Lippert-Mataga relationship and higher than values obtained from Reichardt-Ravi relationship. It has been found that the fluorescence lifetime of both compounds was found to decrease as the emission energy increases and being higher for (II) than for (I), and also was found to increase as the solvent’s dielectric constant increases. All photophysical properties were found to correlate well with Reichardt’s solvent polarity parameter, ETN. We have employed Kamlet-Taft, Catalán and Laurence et al. multi-parametric relationships to assign the contribution of the specific and non-specific solute–solvent interactions. Non-specific interactions were found to be mostly dominating in all cases.

Synthesis and third order optical nonlinearity studies of toluidine tartrate single crystal supported by photophysical characterization and vibrational spectral analysis

The organic nonlinear crystal Toluidine Tartrate (TT) was synthesized, its structure was reinvestigated by X-ray diffraction analysis and investigated theoretically as well as experimentally to examine its nonlinear optical (NLO) behavior. The electron transport mechanism and hydrogen bonding interactions in TT have been explored using the Natural Bond Orbital analysis and optimized geometry calculations. The vibrational spectral investigations of the compound have been carried out using the experimental and computational FT-IR and FT-Raman analyses. UV–vis spectral investigations show the optical absorption of TT crystal at 271 nm and 319 nm and reveal its optical transparency in the visible region. The HOMO LUMO study reveals a 4.5388 eV energy gap which shows its reactivity. Photoluminescence and lifetime studies show a near violet emission with considerable lifetime. The thermal property of the sample was analyzed by TG and DTA analysis and it was found that the TT crystalline compound is stable up to 201 °C. Hyperpolarizability calculations give an augmented value of hyperpolarizability. Z-scan measurements in the pulsed as well as continuous wave laser excitation regimes reveal a substantial decrease in normalized transmittance at higher laser fluences, substantiating the nonlinear behavior and optical limiting application of TT crystals.

The solvatochromism and aggregation-induce enhanced emission of triphenylamine substituted styrene derivatives and its application in dye sensitized solar cells

Five new triphenylamine (TPA) based D-π-A structural motifs were strategically designed and synthesized in high purity. The photophysical, electrochemical, photovoltaic properties were studied and the optimized geometry calculations of D-π-A chromophores and dyes were ascertained by DFT and TD-DFT methods. Photoluminescence properties of all the chromophores were studied in different organic solvents as well as in aggregated states. Three chromophores emit blue fluorescence in ethanol solution. However, two chromophores TPA-PHA [(E)-4′-(4-(diphenylamino)styryl)-[1,1′-biphenyl]-4-carbaldehyde], TPA-PFA [(E)-4′-(4-(diphenylamino)styryl)-2-fluoro-[1,1′-biphenyl]-4-carbaldehyde] exhibited Aggregation-induced emission enhancement (AIEE) revealing the formation of excimer in excited state. The TPA-PFA had lesser quantum yield than TPA-PHA in an aggregated state, since the m-fluorine substitution on phenyl containing chromophore makes an “inductive effect”. Substitution of aldehyde group causes enhanced formation of ICT from donor to acceptor. From FE-SEM analysis we concluded that both AIEE chromophores exhibit two different kinds of “nano-aggregates” in the solid state. The AIEE chromophores (TPA-PHA and TPA-PFA) and its derivatives i.e., Dye-1, Dye-2 were utilized in DSSC application for the first time. The dye-1 and dye-2 exhibit power conversion efficiencies (PCE) of 1.9% (Jsc = 4.68 mA/cm2, Voc = 0.70 V and FF = 0.59) and 2.1% (Jsc = 5.05 mA/cm2, Voc = 0.68 V and FF = 0.61), respectively.

Revisit of 4,4′-Diaminodiphenyl Sulfone Photophysics in Different Solvents

This paper aims at getting the origin of dual emission of 4,4′-diaminodiphenyl sulfone (Dapsone) in various solvents using steady state and time-resolved emission spectroscopy in conjunction with ground and excited state optimized geometry calculations in gaseous phase and in solvents. The dual fluorescence in different solvents and a distinctive bathochromic spectral shift of the low energy band in polar solvents indicate the possibility of intramolecular charge transfer (ICT) from the donor site (−NH2) to the acceptor moiety in the excited state. Time-resolved emission spectra (TRES) and more precisely time-resolved area normalized emission spectra (TRANES) depict the evolution of the dynamics of excited state species and the charge transfer. Hindrance of rotational relaxation in restricted environments causes intensified charge transfer emission quantum yield. A plausible model for excited state deactivation through ICT has been proposed on the basis of both theoretical and experimental findings. The o...

Structures and vibrations of p-dimethoxybenzene conformers in the S 0 and S 1 states studied by ab initio calculations and resonant two-photon ionization spectroscopy

Detailed data on the structures and vibrations of the p-dimethoxybenzene (PDMB) conformers in the S 0 and S 1 states have been obtained by ab initio calculations and resonant two-photon ionization (R2PI) spectroscopy. Results from optimized geometry calculations show that several conformers (assuming the methoxyl groups are a point) exist in the S 0 state. However, only the cis and trans planar conformers appear as stable species in the S 1 state. The S 1 ← S 0 transition causes the ring to expand and the ring COCH 3 bond to shrink, indicating an enhanced interaction between the ring and the methoxy substituent of PDMB in the excited state. The R2PI spectrum displays two series of bands with respect to the two band origins separated by 221 cm −1. These features can be well correlated to the cis and trans conformers involved in the electronic excitation. Computed results on normal vibrational frequencies also enable us to assign the spectral bands observed.