Frontier molecular orbital analysis of dual fluorescent dyes: predicting two-color emission in N-Aryl-1,8-naphthalimides

A 3 x 3 matrix of disubstituted N-aryl-1,8-naphthalimides was synthesized for the evaluation and discovery of dual fluorescence (DF). The matrix elements included for this study were based on a predictive model that is proposed as a seesaw balanced photophysical model. This model serves as a guide to optimize the dual fluorescence emission from N-phenyl-1,8-naphthalimdes by appropriate placement of substituent groups at both the 4-position of the N-arene as well as the 4'-position of the naphthalene ring. Steady-state fluorescence studies under a variety of solvents indicate that four of the nine dyes in the matrix are dual fluorescent. To provide a more quantitative description of the model, cyclic voltammetry experiments were used to calculate HOMO/LUMO energies of the aromatic components that comprise these DF dyes and give evidence in support for potential mixing of S-1 and S-2 excited states. Given the difficulties in predicting excited state properties such as molecular fluorescence, this ratio of four out of nine hits' for discovering DF signifies proof of principle for this proposed model and should provide a rational basis for the synthesis of future DF 1,8-naphthalimide systems.