Inter- and intramolecular electronic interactions: Part 1. The formation and behavior of fluorescent Lewis acid-base exciplexes and triplexes. Part 2. Polyarylureas

Part 1. The excited singlet states of trans -3-aminostilbenes and 9-aminophenanthrene and their N-aminoalkyl derivatives are strongly fluorescent in cyclohexane. Addition of low concentrations of Et₃N, Pr₂NH, or PrNH ₂ results in red-shift of the emission maximum and moderately decreased fluorescence intensity. Analysis of the fluorescence behavior using a combination of Singular Value Decomposition with Self-Modeling and kinetic analysis provides evidence for the sequential formation of a 1:1 complex (exciplex) and 1:2 complex (triplex) between the excited arylamines and ground state alkyl amine, both of which are strongly fluorescent. Both the formation and decay of the exciplex and triplex are dependent upon the extent of amine N-alkylation. Excited state complex formation is attributed to a Lewis acid-base interaction between the excited aminophenanthrene and ground state amine.; Part 2. The molecular structure and absorption and fluorescence spectra of tertiary N,N′-dipyrenyl- and dinaphthylureas have been investigated and compared to the properties of N,N,N′-trimethyl-N ′-arylurea model compounds. The diarylureas exists predominantly as a mixture of folded (E,E) syn and anti rotamers that interconvert via flipping of one of the arene rings to unfolded (E,Z) rotamer geometries. The absorption and fluorescence spectra of the diarylureas at 77 K in a rigid glass are similar to those of the model compounds. However, in fluid solution, the diarylureas exhibit both excimer fluorescence and monomer fluorescence. This behavior is attributed to rotational equilibrium between folded rotamers exhibiting excimer fluorescence and unfolded rotamers which exhibit monomer fluorescence. The behavior of the diarylureas is compared to that of other systems that form intramolecular excimers.; Polyarylurea oligomers have been reduced with alkali metal. Transient formation of arylurea anion radicals leads to reductive elimination of the urea linkages, to form the anion radicals of the corresponding oligoaryls. The reactions are intramolecular and sequencing remains intact. The p _π orbitals of the adjacent ipso carbons evolve into aryl-aryl sigma bonds of the oligoaryl anion radical products. Although similar behavior has been observed for more constrained π-stacked systems, the urea linkages provide a novel architecture for templating aryl-aryl bond formation in oligomeric systems.