Conformational Effects on the Lowest Excited States of Benzoyl-Pyrrolopyridazine: Insights from PCM Time-Dependent DFT

Abstract

Time-dependent density functional theory (TD-DFT) computations and steady-state electronic spectroscopy measurements are performed on two recently synthesized pyrrolopyridazines to account for the detrimental effect of benzoyl substitution on the blue fluorescence emission. In the case of the highly fluorescent ester derivative, planar in ground state, we show that TD-DFT using the PBE0 and B3LYP hybrid functionals in the state-specific solvation approach provides an accurate description of absorption and emission properties. In benzoyl-pyrrolopyridazine, the (pretwisted) orientations of the benzoyl group and the solvent polarity are both found to modulate the nature of the lowest excited states. The first excited state has nπ* character at ground-state geometry of the main conformer (carbonyl group facing the diazine ring) in nonpolar solvents and become nearly degenerate with a ππ* state in polar solvents. The latter, lower than the nπ* state at the ground state geometry of a minor conformer, relaxes into a twisted intramolecular charge transfer. Experimental absorption and excitation spectra are consistent with the conformational-dependent picture of the lowest excited state (as derived from TD-DFT). A rather qualitative agreement in predicting the fluorescence emission wavelength is achieved in computations employing the CAM-B3LYP and BH&HLYP functionals, whereas global hybrids with low or moderate amounts of exact exchange exhibit the expected TD-DFT failure with up to 1 eV underestimated transition energies.

Spectroscopic signatures and structural motifs in isolated and hydrated theophylline: a computational study

“…RI-CC2 implementation in Turbomole 6.4 employing the basis set 6-311++G(d,p) was also used to compute the vertical excitation energies (VEE) of the theophylline monomer, using CC2/aug-cc-pvdz optimized geometry. The effect due to the so-called bulk water molecules was taken into account within the polarizable continuum model (PCM) [37][38] and the conductor like screening model (COSMO) framework. 38 The electronic absorption spectra in aqueous solution have been calculated by employing the B3LYP hybrid exchange correlation functionals, using the PCM and COSMO continuum solvent models.…”

“…The effect due to the so-called bulk water molecules was taken into account within the polarizable continuum model (PCM) [37][38] and the conductor like screening model (COSMO) framework. 38 The electronic absorption spectra in aqueous solution have been calculated by employing the B3LYP hybrid exchange correlation functionals, using the PCM and COSMO continuum solvent models. [35][36][37][38][39] In this work, the lowest excited 1 ππ* state of theophyllinne was optimized at the TD-B3LYP/6-311++G(d,p) and TD-PBEO 40 / TZVP levels of theory implemented in Turbomole V6.4.…”

“…Thus the blue shift in complexes II and III reflects a decrease in the binding energy upon electronic excitation by 387 and 564 cm -1 , respectively. The effect of hydration on S 1 ( 1 ππ* ) excited state due to bulk water environment, mimicked by the polarizable continuum model (PCM)[37][38] and conductor like screening model (COSMO),39 both show a small blue shift in accordance with the result of experimental electronic absorption spectra in aqueous solution 19. The corresponding VEE to S 2 ( 1 nπ*) state for each O-bonded Thp 1 -(H2O) 1 complexes were blue shifted.…”

Electro-Optical and Spectral Comparative Study of Some Triazolium Methylids with Biomedical Applications

“…Structural formula of the studied 1,2,4-triazolium ylids geometry optimization of the studied compounds. Four carbanion monosubstituted 1,2,4-triazolium ylids were synthesised [18] and studied from structural and spectral point of view. The structural features of the studied ylids result from the scheme 1 and table 1.…”

Microwave Assisted Reactions of Fluorescent Pyrrolodiazine Building Blocks

“…Azaindolizines derivatives represent such a class (with 10 π-electron N-fused heterocycles, containing a bridgehead nitrogen atom shared by an electron-excessive pyrrole and a diazine electron deficient six-membered ring) being a ‘pure’ blue-emitting moiety. [15,16]. This uneven π-electron distribution between the two fused rings is an important feature that leads to electron delocalization.…”