Computational Investigations on Excited State Properties of Cyanine Dyes and Carbene-bound Main Group Elements

  • Author / Creator
    Momeni Taheri, Mohammad Reza
  • The first section of this thesis is concerned with the computational study of excited state properties of boron-dipyrromethene (BODIPY) organic dyes using ab initio and time-dependent density functional theory (TD-DFT) methods. Through a comprehensive benchmark of TD-DFT methods against experiment for the BODIPY and Aza-BODIPY families, it was found that all TD-DFT methods systematically overestimate excitation energies. However, due to the high linear correlation of TD-DFT results with experiment, most functionals were found to be useful in predicting the excitation energies if corrected empirically. Through extensive examination of common TD-DFT problems (i.e., charge transfer (CT), multi-reference (MR) and double electron excitations), the deviation from experiment for TD-DFT was found to originate from contributions of multi-reference character and double electron excitations for the BODIPY family. We determined that the local coupled cluster method (LCC2) offered the best compromise between accuracy and efficiency for these systems. An extensive benchmark study on vertical excitation energies of 11 different BODIPY and Aza-BODIPY dimers was performed using 15 different TDA-DFT methods. Adiabatic excitation energies were obtained for all structures using the M06-2X meta hybrid functional. Among the TDA-DFT functionals used, B2GP-PLYP and PBE0-2 double hybrid density functionals were found to yield the least amounts of mean absolute deviations (0.188 and 0.202 eV, respectively) when compared to experiment. The possible applications of BODIPY and Aza-BODIPY dimers in photodynamic therapy were examined by determining their spin-orbit coupling matrix elements, CASSCF occupancies along with the LCC2 vertical excitation energies and [S0-T1] and [S1-T1] singlet-triplet gaps. A systematic study on possible azo-linked BODIPY and Aza-BODIPY dimers was accomplished and novel near infrared heavy atom free dyes were introduced. In the second section of this thesis, the chemistry of carbene bound borane and silane adducts is discussed extensively with a particular focus on the propensity of these adducts for C-N bond cleavage of the carbenic species. A significant difference was observed between N-heterocyclic carbenes (NHCs) and aminoalkyl carbenes (Me}CAAC) in terms of the propensity of their element hydride complexes to participate in ring expansion chemistry. The computations showed that formation of a ring expanded product from ImMe2-BH3 is kinetically unfavourable due to the high energy barrier for the H-atom migration from boron to carbon. In the case of the silane adducts with NHC, the simultaneous presence of at least one hydrogen atom and one phenyl ring is crucial as the ring expansion reaction is not likely to happen for SiH4 and SiPh4; these computational findings are in agreement with the experimental observations. Bonding analyses of boron-nitride substituted adducts with N-heterocyclic carbenes and phosphino yilides were carried out using EDA-NOCV, NBO and AIM techniques. Considering the Gibbs free energies, values greater than -50 kcal/mol were found for the complexation energies. From the NBO, AIM and EDA-NOCV approaches, the existence of a polar covalent bond between carbene and the boron atom was confirmed in each adduct studied. A donor-acceptor strategy showed that LB(BN)n-W(CO)5 (n = 1-3) complexes could be experimentally achievable (LB = Lewis base). Finally, analysis of the EDA-NOCV results in these adducts showed that the carbene-boron bonds are stronger in the presence of W(CO)5 as a Lewis acid mainly because of a dramatic decrease in Pauli repulsion rather than an increase in the electrostatic/orbital attraction.

  • Subjects / Keywords
  • Graduation date
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Department of Chemistry
  • Supervisor / co-supervisor and their department(s)
    • Brown, Alex (Chemistry)
  • Examining committee members and their departments
    • West, Frederick (Chemistry)
    • Jacquemin, Denis (Chemistry, University of Nantes)
    • Veinot, Jonathan (Chemistry)
    • Klobukowski, Mariusz (Chemistry)
    • Xu, Yunjie (Chemistry)