Isomerization Dynamics of 1,1’-Diethyl-4,4’-Cyanine (1144C) Studied by Different Third-Order Nonlinear Spectroscopic Measurements

Abstract

The isomerization of 1,1'-diethyl-4,4'-cyanine (1144C) in two solvents, ethanol and hexanol, was studied by three different third-order four-wave mixing techniques: three-pulse photon echo peak shift (3PEPS), transient grating (TG), and pump-probe (PP) to provide complimentary information on different aspects of the reaction dynamics. A double-sided Feynman diagram analysis was used to assist in the formulation of the kinetic behavior in the TG and PP signals. The ground-state recovery process can be described as a single exponential process which is dominated by the bond-twisting motion on the excited-state surface. The rate is strongly viscosity and temperature dependent. A larger yield of the isomer is obtained in less viscous solvents or with greater excess excitation energy. Apparently, contradictory wavelength-dependent decay behavior was found in the TG and PP signals. This can be understood by considering the different real and imaginary contributions to the signals from hot ground-state absorption and its subsequent recovery to the equilibrated state and from the product state. I. IntroductionThe development of short laser pulses has made it possible to explore molecular motions on the time scale of femtoseconds via the nonlinear optical response. 1-3 Many different nonlinear spectroscopic techniques have been developed to probe different aspects of the molecular dynamics. 2,3 The third-order nonlinearity is the lowest order nonzero term in isotropic media and has been exploited to study the reaction dynamics in various types of four-wave mixing spectroscopies, 3-7 including photon echo, transient grating, and pump-probe measurements.The three-pulse photon echo peak shift (3PEPS) is a novel technique that has been applied by our group and others to study solvation dynamics and energy-transfer processes for several years. 5,[8][9][10][11][12] The insensitivity of 3PEPS to the excited-state lifetime makes it a suitable technique to study solvation dynamics and solvent effects in reactive systems. 7,13 One distinct feature of 3PEPS is its capability of differentiating the rephasing contribution and the free induction decay (FID) contribution, which contribute in a similar way to conventional populationbased techniques, such as fluorescence up-conversion, pumpprobe (PP), and transient grating (TG) spectroscopies. 5,10 This is the basis of the application of 3PEPS in the study of energy transfer. 10 Recently, we extended the 3PEPS technique to the study of reactive systems, such as electron transfer in electrondonating solvents 7 and torsional dynamics of the triphenylmethane (TPM) dye molecules. 14 Since 3PEPS is not sensitive to the excited-state lifetime, it can provide information on processes such as solvation and vibrational relaxation during reactions. Similar information is difficult to obtain from population-based techniques. Therefore, a combination of 3PEPS with population-based techniques such as TG or PP is attractive for the study of solution-phase reactive systems.Photoinduced isomerization rea...

Femtosecond study on the isomerization dynamics of NK88. I. Ground-state dynamics after photoexcitation

“…All transients represent the difference ⌬A of the absorption signal with and without pump pulse. The dynamics of the measured transients are approximated in a single or multiple exponential fitting procedure, as widely used in femtosecond transient spectroscopy, [32][33][34][42][43][44][45][46][47][48] with rise and decay times taking into account the cross correlation ͓200 fs full width at half maximum ͑FWHM͔͒ of the pump and the white-light probe laser pulses.…”

Four-wave mixing signals from β-carotene and its n = 15 homologue

“…In order to scale the response functions according to the population kinetics, each response function has to be separated into a nuclear and an electronic population kinetic component (Yan and Mukamel 1991;Xu et al 1999;Xu and Fleming 2001;Stenger et al 2002;Xu et al 2002;Jimenez et al 2004;Nibbering and Elsaesser 2004). For example, R 2 is scaled as a function of the population time T according to the corresponding kinetics of the S 2 state with the decay rate C. In this case, we can write R 2 ¼ R 0 2 exp½ÀCT, where R 0 2 represents the nuclear dynamics; the population kinetic component exp[-CT] has been separated.…”

Visualizing overdamped wavepacket motion: Excited-state isomerization of pseudocyanine in viscous solvents

“…Being the first step in vision, photoinduced isomerization is also the key process in nature. To characterize the excited-state dynamics leading to the formation of an isomer product (hence, excited-state isomerization -ESI), many time-resolved experimental approaches, including gas-phase photoelectron spectroscopy [2], fluorescence up-conversion [3], transient absorption [4], time-resolved stimulated Raman scattering [5], and three-pulse photon-echo spectroscopy were utilized [6,7]. These experiments targeted a wide variety of biologically relevant samples, e.g., retinal chromophores of rhodopsin [4,5], bacteriorhodopsin [8] and tetrapyrrole phycocyanobilin [9] as the system that mimics the phytochrome chromophore [10].…”