Reaction Dynamics of a Photochromic Fluorescing Dithienylethene

Abstract

The interplay of photochromism and fluorescence was studied by attaching anthracene as chromophore to dithienylperfluorocyclopentene (1,2-bis[5-anthryl-2-methylthien-3-yl]perfluorocyclopentene, Ac-BMTFP). The blue fluorescence of the open isomer of Ac-BMTFP is suppressed by the ring-closure reaction. The spectroscopic properties and the reaction dynamics of this compound were characterized by measurements of the fluorescence yield and decay dynamics, and the quantum yields of the photochromic ring-closure and ring-opening reactions, as well as the spectra and time evolution of reaction intermediates. The data are analyzed in terms of a model potential and single-electron density matrices, which are calculated using the collective electronic oscillator (CEO) approach and the INDO/S semiempirical Hamiltonian. For the ringopening reaction, single-exponential decays with a time constant of 8 ( 0.5 ps were determined for the photoinduced bleaching and absorption transients. In contrast, because of the presence of reacting and nonreacting conformers, the dynamics measured for ring closure are more complex. Both conformers of the open isomer undergo a fast electronic-conformational relaxation on a time scale of ≈0.9 ps after excitation of the S 1 or S 3 state. Nonreacting conformers fluoresce with a distribution of lifetimes ranging from less than 100 ps to more than 400 ps. Reacting conformers reach a precursor state with a lifetime of 10 ps from which the ring-closure reaction takes place. The rates of the ring-opening and ring-closure reactions are determined as 9.5 × 10 9 and 6 × 10 10 s -1 , respectively. Rather than being a drawback, the presence of different conformers in the sample is argued to be a requirement for applications relying on efficient switching of the fluorescence.

Fluorescent Switches Based on Photochromic Compounds

“…Furthermore, similar operating principles can be extended from fluorophore-photochrome dyads to fluorophore-photochrome-fluorophore triads. [26,[36][37][38] The molecular dyad 9a ( Figure 2) integrates an oxazine fluorophore with a fulgide switch within its molecular skeleton. [29] The photochromic component ring closes upon ultraviolet irradiation.…”

Theoretical Photochemistry of the Photochromic Molecules Based on Density Functional Theory Methods

“…However, these modifications may change or completely eliminate the photochromic ability. Theoretical studies are indispensible to understand the reason of these changes and to formulate the guiding principles for the rational molecular design ( [6] and [7]). However, as Nakamura et al state in their recent review [7], the accurate relative energies of the excited states in real size molecules are still very difficult to calculate, because it requires the balanced description for both covalent (2A state) and ionic states (1B state).…”

Ring Closure Reaction Pathway of a Diarylethene in Solution Using Femtosecond Time‐resolved Fluorescence Spectra

“…The isomerization from the open isomer to the closed isomer is initiated by ultraviolet (UV) irradiation, while the reverse reaction by visible light. 4,5,[11][12][13][14][15][16][17][18][19][20][21][22][23] However, large variation in the reaction rates obscures the analysis of the reaction dynamics. According to the Woodward-Hoffmann rule, 6 only the antiparallel isomer can be converted to the closed form by photoexcitation.…”

“…The closed isomer has a single conformation, whereas the open isomer has two conformations, parallel and antiparallel, depending on the direction of the aryl moieties as shown in Scheme 1. 19 However, femtosecond transient absorption (TA) experiment for thiophene oligomer with a diarylethene structure yielded the ring closure time of 1.1 ps. It is known that the photochromism of a diarylethene is preserved even in polymer chains and single crystalline phase.…”