Experimental and Computational Investigation of the Photophysical Properties of a Series of Luminescent D-A-D' and D-A-A' Pyrimidines

Pyrimidines, a prominent isomer class of diazines, are promising molecular constituents of electron-deficient luminescent and hole-transport materials. Here, we report the fluorescence lifetimes and describe the electronic structures and character of low-lying emissive excited states of a series of synthetically accessible donor-acceptor-donor (D-A-D') and donor-acceptor-acceptor (D-A-A') type pyrimidines, including both all-organic and hybrid organic-organometallic analogues. We find that strategically varying the aryl substituents on a pyrimidine enables tuning of the character of the luminescent excited states from charge-transfer (CT) to locally excited (LE) states, which then differ in their sensitivity to their environment. This study suggests structural handles for controlling the photophysics of arylpyrimidines relevant to a variety of applications for luminescent materials.