New Dual Fluorescent Dyes Based on Modified “Excited State with Extended Conjunction” Photophysical Model
This review presents research that centers on verification of a new photophysical model for the excited state properties of N-phenyl-1,8-naphthalimides. The first section of the review highlights the critical advantages that two-color dyes possess relative to single color dyes with respect to internal calibration and quantitative analysis. Recent examples are provided to show the development of the modified photophysical model and the fluorescence properties on which this model is based upon. Results shown in this section serve as a guide or roadmap toward future strategies, specifically, which substituents are required for the promotion of dual fluorescence (DF). Based on these concepts, a 3×3 matrix of substituted N-aryl-1,8-naphthalimides was synthesized for the evaluation and discovery of DF. The matrix elements included for this study were based on a predictive model that we propose as a seesaw balanced photophysical model. This model serves as 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 4ʹ-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. 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.
KeywordsHigh Quantum Yield Naphthalene Ring Long Wavelength Band Twisted Intramolecular Charge Transfer Dual Fluorescence
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