The Photoaddition of Alcohols to Methoxy Substituted Stilbenes

Trapping the Phantom Excited Singlet State

Research Mentor: Dr. Jack Saltiel,
Department, College, Affiliation: Chemistry and Biochemistry, Arts and Sciences
Contact Email: jsaltiel@fsu.edu
Research Assistant Supervisor (if different from mentor): Dr. Sumesh Babu Thomas
Research Assistant Supervisor Email:
Faculty Collaborators: Dr. Edwin Hilinski
Faculty Collaborators Email: hilinski@chem.fsu.edu

Looking for Research Assistants: Maybe one more
Number of Research Assistants: 2
Relevant Majors: Prefer Chemistry majors interested in graduate school.
Project Location: On FSU Main Campus
Research Assistant Transportation Required: Yes
Remote or In-person: In-person
Approximate Weekly Hours: At least 10 hours/week, Flexible schedule (Combination of business and outside of business. TBD between student and research mentor.)
Roundtable Times and Zoom Link: Not participating in the Roundtable

Project Description

UROP Project Saltiel Laboratory
The Mechanism of Ether Formation from the Photoaddition of Alcohols to p- and m-Methoxystilbenes
The photoaddition of methanol, ethanol and 2,2,2-trifluoroethanol (TFE) to methoxy-substituted stilbene derivatives was described by Roberts and Pincock. [1] The position of the methoxy group was shown to have an enormous effect on the fluorescence efficiency (quantum yield, QYf) of the stilbene. [2] Measured fluorescence yields in acetonitrile are 0.007 and 0.16 for t-p-MeOSt and t-m-MeOSt, respectively, Chart 1. [2] TFE quenches the fluorescence of the trans-isomers and they concluded that this was due to protonation of the trans-stilbene singlet excited states (1t*). The resulting cations react with the alkoxide ion to give ether by coupling, or bibenzyl products by hydride transfer. [2] Ether also forms following rearrangement to a carbene intermediate. [1-4] Our more recent work with the unsubstituted stilbenes established that the major protonation pathway follows torsional relaxation of 1t* to a common zwitterionic twisted intermediate, 1p* that is also accessed from the cis-stilbene singlet excited state, 1c*. [3] The mechanism is shown for deuterated methanol in Scheme 1. Consequently, we have questioned Pincock’s conclusion that protonation precedes torsional relaxation. [3] Studying the initial formation of the ethers starting from the pure trans- and cis-isomers of p-MeOSt and m-MeOSt will allow evaluation of the degree to which ether formation involves 1t* or 1p*.
References
(1) Roberts, J. C.; Pincock, J. A. The Photochemical Addition of 2,2,2-Trifluorethanol to Methoxy-Substituted Stilbenes. J. Org. Chem. 2004, 69, 4279-4282.
(2) Roberts, J. C.; Pincock, J. A. Methoxy-substituted stilbenes, styrenes, and 1-arylpropenes: Photophysical properties and photoadditions of alcohols. J. Org. Chem. 2006, 71, 1480-1492.
(3) Saltiel, J.; Gupta, S. Photochemistry of the Stilbenes in Methanol. Trapping the Common Phantom Singlet State. J. Phys. Chem. A 2018, 122, 6089-6099. Woning, J.; Oudenampsen, A.;
(4) Laarhoven, W. H. Photochemical Addition of Methanol to Stilbenes. J. C. S. Perkin Trans. 2 1989, 2147-2154.


Research Tasks: The undergraduate research project consists of securing the pure trans-isomers of p-MeOSt and m-MeOSt and synthesizing the cis-isomers using triplet sensitized photoisomerization followed by column liquid phase chromatography. Addition of alcohols in parallel to the two pairs of isomers will be carried out in a Merry-Go-Round apparatus and the progress of photoisomerization and ether formation will be determined by gas phase chromatography using a flame ionization detector. Products will be separated by liquid chromatography and their purity will be determined by 1H NMR and UV spectroscopies. This research should determine whether the mechanism in Scheme 1 applies to the methoxy-substituted stilbenes.


Skills that research assistant(s) may need: Having had the CHM 2210 and 2211 Organic Chemistry courses would help.