Design and Synthesis of Red-Absorbing Fluoran Leuco Dyes Supported by Computational Screening

We report here on the design and synthesis of red-absorbing fluoran leuco dyes (LD). An essential part of the present dye development process is a computational screening of the candidate molecules, which allows for both time-efficient and accurate in silico characterization of the dyes. We focus our study here on the robust benzo[a]fluoran scaffold frequently used in leuco dyes. For the computational screening of LD candidates, an automated DFT-based simulation protocol has been developed and applied. The protocol consists of a combinatorial generation of the molecular structures of possible LD candidates, followed by simulations of their optimized molecular geometries, with their UV-Vis spectra as the main figure of merit. In the present application of the simulation protocol, more than 1600 structures of possible LD candidates have been evaluated. Finally, two structures, LD01 and LD02, have been chosen from the list of the best computed LD candidates to be synthesized and characterized. Our study demonstrates how the synergy between experiment and simulation can facilitate the design of novel leuco dyes.