Transient optical absorption spectroscopy of the photochemical spiropyran-merocyanine conversion

Abstract

The photochemical ring-opening reaction of 1',3',3'-trimethylspir~[2H-l-benzopyran-2,2'-indoline] has been followed by transient absorption spectroscopy, covering the range 370-650 nm with a temporal resolution of 0.42 ps. During the pump pulse, induced transient absorption is observed only at wavelengths shorter than 500 nm, with a maximum near 440 nm. The absorption at 440 nm decays within K 5 ps, while a broad absorption band appears at 550 nm in the region characteristic of merocyanine absorption. The risetime of the absorption at 550 nm is approximately 1.3 ps. The reaction is described as a barrierless photoisomerisation on the excited singlet potential energy surface towards a-nonplanar cisoid form, followed by internal conversion and

Overtone State‐Selective Isomerization by a Series of Picosecond Infrared Laser Pulses: Model Simulations for Be2H3D‐(C2v) → C3v)

“…• The parameters £? and O)k are tuned to be optimal for the respective individual transition (38) implying three pump pulses and one dump pulse. Thus, the series of K=4 laser pulse sshould induce the sequence of one-photon vibrational transitions i.e., the reaction leads, from the ground state of the reactant isomer to the third excited state of the product isomer .…”

Ultrafast ring-opening and solvent-dependent product relaxation of photochromic spironaphthopyran

“…However, the time scale for the ring-opening reaction remains a debated point. In the early 90's, Ernsting and coworkers reported the results of optical pump-probe experiments in the visible range carried out on BIPS solutions in n-pentane 16,17 as well as ethanol 18 and observed the formation of merocyanine species upon excitation at 308 nm with a rise time of B0.9 ps. They found that the spectrum in the 450-600 nm range at 30 ps resembled that of one recorded in the microsecond timescales suggesting that the product is well-established within this time frame.…”

Photochemistry of Merocyanine 540

“…3(b). Neither the yield nor the identity of this species have been elucidated, although it is unlikely to be a spiropyran formed by rearrangement of the cisisomer (Ernsting, 1989), and will be addressed in a later study employing time-resolved resonance Raman detection facilities. The absence of any apparent 02-quenching effect implies that this tranwavelength/ nm Figure 4.…”