Interplay of Intramolecular Charge Transfer and Exciton States in pi-Extended Triptycenes Enhances Mid-Spectrum Absorbance Intensity and Fluorescence Quantum Yields

Strategies for tuning the optical properties of organic chromophores generally focus on shifting the edges of the spectrum, this might be red-shifting the longest absorbance band to improve solar absorbance, or blue-shifting of the highest energy emission band towards deep blue emission. In contrast, strategies to enhance molar absorptivity and control excited state rate constants are less obvious with intermolecular excitons, J-aggregates, providing one of the most powerful approaches. Here, a homologous series of π-extended triptycenes are presented which reveal routes to control both aspects while also providing an explanation for enhanced optical properties previously observed in donor-acceptor triptycenes and related three-dimensional chromophores. These molecules have electronic spectra consisting of two distinct regimes, a low energy intramolecular charge transfer and a mid-spectral progression characteristic of a J-aggregate-like exciton state but occurring entirely intramolecularly. This integration of a rigid 3D scaffold with functional all-ring-fused chromophores thereby results in systematic amplification of mid-spectrum absorbance intensities and high fluorescence quantum yields. Our findings underscore the importance of 3D structure design in achieving superior optoelectronic performance, thus offering a pathway for the development of advanced molecular materials for organic photovoltaics and light emitting devices.