Reaction dynamics of photochromic dithienylethene derivatives

Abstract

Ž. The reaction dynamics of the photochromic ring-opening reaction of 1,2-bis 5-formyl-2-methyl-thien-3-yl perfluoro-Ž . cyclopentene CHO-BMTFP in dichloromethane solution was investigated using femtosecond transient absorption spectroscopy. The data were analyzed in terms of a model potential and single-electron density matrices, which were calculated Ž . using the collective electronic oscillator CEO approach and the INDOrS semiempirical Hamiltonian. The S -S and 0 1 S -S transitions of the closed isomer were resonantly excited using 120 fs pump pulses at 610 and 410 nm, respectively. A 0 2 temporally delayed white light continuum probe pulse monitors the decay of the S or S state as well as the recovery of the 1 2 S state. Within the first picosecond after excitation, CHO-BMTFP was observed to undergo a fast structural relaxation 0 along the S potential energy surface into a minimum constituting a precursor of the ring-opening process. The rather long 1 lifetime of the precursor, t s 13 ps, was consistent with the calculated potential barrier in front of the conical intersection 2 with the S potential energy surface, which may arise from stabilization of the nearly planar closed isomer by an efficiently 0 delocalized p-electron system. q

Photoswitching Behavior of a Cyclohexene‐Bridged versus a Cyclopentene‐Bridged Dithienylethene System

“…The PES of the first excited singlet state shows a global minimum which coincides with the minimum of the closed form in the ground state, and a shallow local minimum at a CC distance of around 2.3 Å (except for 2 calculated with BP86), which cannot be clearly distinguished from a numerical error. In the work of Nakamura and co‐workers42 the PES for the first excited state of the ethenyl‐bridged switch obtained with CASSCF/CASPT2 shows a similar shallow minimum, so it appears to be a true feature of the excited‐state PES.…”

Photochemical investigation of a photochromic diarylethene compound that can be used as a wide range actinometer

“…28, 29 The lowest energy band of most open isomers closely resembles, in shape and position, the first excitation of the free aryl groups, 28,30,31 and thus can be attributed to transitions within the p-system of these chromophores. The broad absorption band of the closed isomers in the visible region reflects the large p-conjugation of the lateral aryl chromophores and the central structure; therefore the red-shifting of these bands correlates with the p-donating ability of the substituents on the aryl rings.…”

Photocontrol on ultrafast excited state transfer processes

“…The dynamics of the photochromic reactions of symmetrically substituted and unsubstituted diarlyethenes have been studied recently by fs-and ps-transient absorption spectroscopy [7][8][9][10][11][12][13] and time-constants of less than 12 ps down to 1:1 ps are reported. Possible applications of diarylethenes in functional photoswitchable systems discussed in the literature rely on the different extension of conjugation in the two isomeric forms.…”