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A ten element matrix of 5- and 6-substituted-(2,3)-naphthalimides was prepared for the appropriate placement of substituents necessary to promote dual fluorescence (DF). As prescribed by our balanced seesaw photophysical model this matrix yielded nine new DF dyes out of a possible ten compounds. From this set of nine DF dyes, 4-fluoronaphthalic amide (37) was selected as a probe for ratiometric detection of DNA and demonstration of panchromatic emission.

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-naphthalimides 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 S1 and S2 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.

The 3 x 3 matrix elements included for the evaluation of dual fluorescence are based on a predictive model described as a 'seesaw balanced' photophysical model.

Three isomers of hydroxy substituted N-aryl-1, 8-naphthalimides based on N-aryl naphthalic anhydride fluorophore have been synthesized. The decrease in fluorescence intensity from ortho to para substitution of hydroxy group on N-aryl reveals that para substituted isomer undergoes ESEC (Excited State with Extended Conjugation) mechanism which is proved by low quantum yield and appearance of dual emission. The ortho isomer, however, has high quantum yield and no tautomer emission, indicating ESIPT (Excited State Intramolecular Proton Transfer) mechanism is not operating. Similarly, all these isomers show strong fluorescence quenching in presence of strong H-bonding solvents like DMSO and pyridine, but there was neither the shift of emission bands nor the appearance of new bands for proton transfer to these solvents. Thus, it also indicates the absence of excited state proton transfer mechanism. Both the ortho isomer, and to a greater degree the meta isomer, showed larger quenching constants (Kapp) with pyridine than DMSO. This trend opposes the hydrogen-bond affinity for these solvents with phenol and points to a 2-point recognition interaction. In addition, a naphthalimide derivative using 2-aminoimidazole was prepared and examined for optimal positioning of a six-membered ring hydrogen bond pattern. No dual fluorescence was observed for this compound either.