Circular Dichroism of Helicenes Investigated by Time-Dependent Density Functional Theory

Abstract

It is shown that molecular electronic circular dichroism (CD) can systematically be investigated by means of adiabatic time-dependent density functional theory (TDDFT). We briefly summarize the theory and outline its extension for the calculation of rotatory strengths. A new, efficient algorithm has been implemented in the TURBOMOLE program package for the present work, making large-scale applications feasible. The study of circular dichroism in helicenes has played a crucial role in the understanding of molecular optical activity. We present the first ab initio simulation of electronic CD spectra of [n]helicenes, n ) 4-7, 12. Substituent effects are considered for the 2,15-dicyano and 2,15-dimethoxy derivates of hexahelicene; experimental CD spectra of these compounds were newly recorded for the present work. The calculations correctly reproduce the most important spectral features and greatly facilitate interpretation. We propose assignments of the lowenergy bands in terms of individual excited states. Changes in the observed spectra depending on the number of rings and substitution patterns are worked out and rationalized. Merits and limitations of TDDFT in chemical applications are discussed.

Ternary thiophene–X–thiophene semiconductor building blocks (X=fluorene, carbazole, phenothiazine): Modulating electronic properties and electropolymerization ability by tuning the X core

“…The excitation analysis had been performed by means of Time Dependent Density Functional Theory (TD-DFT) [53][54][55]; calculations were carried out based on geometries optimized by means ADF with the previously described method. For each excitation, the composition of the solution vector of the TD-DFT eigenvalue problem from which the transition dipole moments are computed [56][57][58] in terms of contributions from pairs of occupied and virtual MOs allows a convenient and intuitive analysis of the results in terms of "excitations" from occupied to virtual Kohn-Sham orbitals [59]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 7 We applied the Davidson iterative procedure for the computation of the eigenvalues and the eigenvectors of the TDDFT equation [60].The parameterizations adopted in the excitation analysis and in the theoretical prediction of the UV/Vis spectra are listed in Appendix B.…”

Chiroptical properties from time-dependent density functional theory. II. Optical rotations of small to medium sized organic molecules

“…12 and 45 in order to be consistent with our previous work 14 and other investigations. 12 For other molecules that we have previously studied in Ref. 14, the same computationally optimized structures have been used in this work.…”

“…Not surprisingly therefore, there has been recently an increasing interest in the computation of optical activity related observables by timedependent density functional theory [9][10][11] ͑TDDFT͒. For example, TDDFT implementations for electronic circular dichroism have been presented by Furche et al 12,13 in 2000 and by Autschbach et al 14 in 2002. Vibrational circular dichroism ͑VCD͒ has already been implemented for DFT by Stephens et al in 1996.…”

Synthesis and Characterization of Novel Chiral Conjugated Materials

“…For (+)- [6]helicene 1, the vectors m and μ are parallel and g abs = ∆ε/ε = +7 × 10 -3 (at 325 nm) may be estimated from the reported data [21,128]. CD spectra of [n]helicenes may be calculated by time-dependent density functional theory (TD DFT) to provide the transition moments and the assignments of absolute confi gura tions [129]. In cross-conjugated carbon-sulfur [7]helicene 40, which possesses similar helical geometry but with a relatively smaller helix turn, g abs = ∆ε/ε = -4 × 10 -3 (at 285 nm, ∆ε max = -117 and ε = 3.1 × 10 4 L mol -1 cm -1 ) is estimated based on chiroptical data for the (-)-enantiomer.…”