Structure-property relationships in quinazoline-based photoluminescent emitters

When designing novel chromophores to target specific properties and applications, there is no established procedure for predicting optical and photophysical properties. To facilitate the screening of promising candidates, we attempt at rationalizing the optical and photophysical properties of six quinazoline compounds by examining their S₁ excited-state (anti)aromaticity via the nuclear-independent chemical shift (NICS) indices. The quinazolines were selected to achieve white light or specific wavelength emission, as they are insufficiently explored chromophores for materials chemistry applications. We found that the accumulation of charge density in the quinazoline π* levels in the S₁ state, without the possibility of transferring it to a suitable electron-acceptor, tends to diminish the fluorescence yields in solution. A larger accumulated charge on the quinazoline core increases its antiaromaticity in the Franck-Condon geometry, thus enhancing the dynamical tendency to relieve it. The NICS indices correlate well with the differences in the interatomic distance matrices of the S₁ and S₀ minima (Δ(S₀,S₁)). Thus, they can be used to anticipate the extent of deformation undergone by the quinazoline core during relaxation from the Franck-Condon geometry towards the S₁ minimum. The structure-property relationships are discussed for all quinazoline compounds, including three newly synthesized derivatives developed from readily available, similar precursors. In this work, we demonstrate that the synergy of experimental and theoretical approaches is essential for the rational design of new chromophores with desired properties.