Photophysics and Photochemistry of Intramolecular Stilbene-Amine Exciplexes

Abstract

The photophysical and photochemical behavior of a series of trans-(aminoalky1)stilbenes in which a primary, secondary, or tertiary amine is appended to the stilbene ortho position with a methyl, ethyl, or propyl linker has been investigated. The tertiary (aminoalky1)stilbenes form fluorescent exciplexes and undergo trans-cis isomerization, but fail to undergo intramolecular reactions analogous to intermolecular addition reactions observed for stilbene with tertiary amines. The photophysical behavior of the tertiary (aminoalky1)stilbenes is dependent upon the choice of linker, solvent, and temperature. The secondary (aminoalky1)stilbenes do not form fluorescent exciplexes but undergo intramolecular N-H addition to the stilbene double bond. Unlike the intermolecular reactions of substituted stilbenes with secondary amines, which yield mixtures of regioisomeric adducts and reduction products, the intramolecular reactions are highly selective, providing an efficient method for the synthesis of tetrahydrobenzazepines. Direct irradiation of the primary (aminoalky1)stilbenes results only in trans-cis isomerization. However, irradiation in the presence of the electron acceptor p-dicyanobenzene results in regioselective intramolecular N-H addition to the stilbene double bond. These results are discussed in terms of the mechanisms of direct and electrontransfer-sensitized irradiation.

Photoreduction of trans-4-R-4′-nitrostilbenes with R: OMe, H and NO2 by di- and trialkylamines in polar media

“…The photoreactions of trans-stilbene with tertiary aliphatic amines in solvents of various polarity have been intensively investigated. [1][2][3][4][5] Most effort has been put into the time-resolved studies, including a Hammett correlation for various p-conjugating substituents R in Me 2 NCH 2 R 3 and the direct observation of N,N-diethylvinylamine formed from triethylamine (TEA) by chemically induced dynamic nuclear polarization. 4 The photoproducts of trans-stilbenes generally result from amine and=or H-atom addition to the central double bond.…”

Photo-polymers Containing (S)-Phenylalanine and Stilbene Pendants: Synthesis and Properties of Ionic Polyacrylates

“…This should provide the existence of a suitably high density of fluorophore molecules, which allow the interaction of singlet trans-stilbene with different amines for the observation of appreciable fluorescence quenching. It should be noted that an electron transfer between the electron donor (ground-state amine) and the acceptor molecules (singlet trans-stilbene) lead either to an exciplex or an ion pair of stilbene radical anions type and amine radical cations within a solvent cage [27]. Figure 4a shows the plot of the fluorescence emission spectra for poly(AcPheBzco-DMAQ) in DMF solution, excited at 334 nm and recorded in the presence and absence of monomethyl viologene as electron donor.…”

Temperature‐Dependent Behavior of Protein‐Chromophore Interactions: A Theoretical Study of a Blue Fluorescent Antibody

“…One mechanism for the red‐shifted fluorescence emission and lengthened fluorescence lifetime at higher temperature is the formation of an exciplex, and these authors suggested two complementary scenarios by which this could occur 1. One involved the intimate interaction between a nearby tryptophan (Trp‐A106)and characterized by significant sharing of charge distribution between stilbene and the tryptophan side chain 19. Another posited that subtle changes in the vibronic coupling between the protein environment and the ligand could lead to the observed lifetime increase of the fluorescence emission with temperature 1.…”