Investigating the optical properties of BOIMPY dyes using ab initio tools.

Using a computational approach combining Time-Dependent Density Functional Theory (TD-DFT) and second-order Coupled Cluster (CC2) approaches, we investigate the spectral properties of a large panel of BOIMPY dyes. BOIMPY derivatives constitute a new class of fluorophores that appeared only very recently [Angew. Chem. Int. Ed., 2016, 55, 13340-13344] and display intriguing properties. First, we show that theory is able to reproduce experimental 0-0 energies with reasonable accuracy, and more importantly excellent consistency (R = 0.99). Next, by analyzing the nature of the excited-states, we show that the first electronic transition does not imply a significant charge-transfer character and significantly differs from the one of the parent BODIPYs. Third, we unravel the vibrational modes responsible for the specific band shapes of the BOIMPY derivatives. Finally, using theory to design new compounds, we propose substitution patterns leading to redshifted absorption spectra, up to ca. 1000 nm.