ADF Study of Photoconversion Efficiency Enhancement in Zinc Porphyrin Dyes via Donor–Acceptor Theory and the BCL Model

Using ADF 2023, a recent J.Mol.Model publication shows that the Barrera-Crivelli-Loeb (BCL) model is effective for zinc porphyrin dyes, particularly when excitations involve intraligand charge transfer. Quantifying the donor and acceptor strengths provides insight into the role of the anchor ligand and its impact on solar cell efficiency.

Based on these insights, a strategy was developed to design zinc porphyrin-based dyes with improved photoconversion efficiency. Calculations of donor and acceptor capacities of molecular substituents allow optimization of the push–pull effect, which is limited by the singlet yield and maximized when donor and acceptor strengths are balanced.

Efficiency can be further enhanced by increasing the energy absorbed in Franck–Condon excitations and the SOMO energy, either through incorporation of a second chromophore or by boosting the participation of the anchor ligand in virtual orbitals involved in the excited state. Additional gains in singlet yield can be achieved by increasing contributions from key molecular fragments ({X} and {F}) via stronger acceptor or polarizing capacities.

Applying this approach led to the design of two new pigments, BCL516 and BCL520, with theoretical photoconversion efficiencies of 10.64% and 10.61%, demonstrating the power of rational donor–acceptor tuning in zinc porphyrin dyes.