Dynamics and equilibrium for the formation of fluorescent Lewis acid-base exciplexes and triplexes between 9-aminophenanthrene and aliphatic amines

摘要

The excited singlet states of 9-aminophenanthrene and its N-aminoalkyl derivatives are strongly fluorescent in cyclohexane.Addition of low concentrations of Et_3N,Pr_2NH,or PrNH_2 results in a 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 1 :1(exciplex)and 1 :2(triplex)complexes between the excited 9-aminophenanthrene and ground-state alkylamine,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.Rate constants and equilibrium constants for complex formation follow the order 1 deg-2deg>3deg,analogous to that for the formation of ground-state complexes between amines and the soft Lewis base HgBr_2.Similarly,N-aminoalkyl derivatives of 9-aminophenanthrene form intramolecular exciplexes.Excited-state complex formation is attributed to a Lewis acid base interaction between the excited aminophenanthrene(lone-pair acceptor)and ground-state amine(lone-pair donor).The factors which determine the stability of excited-state Lewis acid base complexes are characteristic of the specific excited-state acceptor.No universal scale of lone-pair donor strength can be expected to describe the formation of such complexes.