T. Reinot

Site Selective and Single Complex Laser-Based Spectroscopies: A Window on Excited State Electronic Structure, Excitation Energy Transfer, and Electron–Phonon Coupling of Selected Photosynthetic Complexes

Site Selective and Single Complex Laser-Based Spectroscopies: A Window on Excited State Electronic Structure, Excitation Energy Transfer, and Electron Phonon Coupling of Selected Photosynthetic Complexes Ryszard Jankowiak,* Mike Reppert, Valter Zazubovich, J€org Pieper, and Tonu Reinot Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States Department of Physics, Concordia University, Montreal H4B1R6 Quebec, Canada Max-Volmer-Laboratories for Biophysical Chemistry, Technical University of Berlin, Germany Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia

Electronic dephasing of APT in glassy films of water from 5 to 100 K: Implications for H‐bonding liquids

Nonphotochemical hole burning was used to characterize the linear electron–phonon coupling and measure the temperature dependence of the pure electronic dephasing of Al‐phthalocyanine tetrasulphonate (APT) in unannealed and annealed hyperquenched glassy films of water (HGW). Below about 10 K, the dephasing is dominated by coupling to the intrinsic two‐level systems (TLSint) of HGW. This dephasing is a factor of 5× faster for unannealed HGW due to its higher TLSint number density. For annealed HGW, the pure electronic dephasing time (i.e., that dephasing associated with the zero‐phonon line), T2*, is 6.4 ns at 5 K, the slowest dephasing time yet reported for a molecular glassy system at this temperature. At higher temperatures, dephasing due to exchange coupling with pseudolocalized modes at 50 and 180 cm−1, which correlate well with the transverse and longitudinal acoustic modes of water, becomes dominant. The exchange coupling mechanism is based on diagonal quadratic electron–phonon coupling. At 100 K, for example, the pure electronic dephasing times (T2*) are close to 1 ps in value for both types of film. Whereas the transverse acoustic mode is Franck–Condon active (S∼0.5), the 180 cm−1 mode is silent (S<0.02). The determination of the electron–phonon coupling parameters and static inhomogeneous broadening (400 cm−1) of APT’s origin band allowed for simulation of the burn temperature dependence of the overall hole profile (zero‐phonon hole plus phonon‐sideband holes). Comparison with experimental profiles shows that the hole profile theory of Hayes et al. [J. Phys. Chem. 98, 7337 (1994)] captures the main features of the temperature dependence.The S value of the transverse acoustic mode is used to quantitatively explain the burn temperature dependence of the saturated intensity of the zero‐phonon hole and its demise at temperatures just above 100 K (due to Franck–Condon forbiddeness). In view of the essentially complete understanding of the electron–phonon coupling and pure electronic dephasing of APT in HGW attained in this work, the data are used for extrapolation to ice (0° C) and water (at temperatures not far above 0° C) in order to connect with recent photon echo studies of optical coherence loss of dye molecules in liquids. The extrapolation predicts an ‘‘average’’ T1‐dephasing time of ∼0.1 ps due to multiphonon (Brownian oscillator) transitions associated with the transverse acoustic mode and subpicosecond pure electronic dephasing due to exchange coupling with the longitudinal mode. It is suggested that the marriage of hole burning and photon echo techniques in studies of glass forming liquids should be a powerful approach to understanding optical coherence loss in liquids.Nonphotochemical hole burning was used to characterize the linear electron–phonon coupling and measure the temperature dependence of the pure electronic dephasing of Al‐phthalocyanine tetrasulphonate (APT) in unannealed and annealed hyperquenched glassy films of water (HGW). Below about 10 K, the dephasing is dominated by coupling to the intrinsic two‐level systems (TLSint) of HGW. This dephasing is a factor of 5× faster for unannealed HGW due to its higher TLSint number density. For annealed HGW, the pure electronic dephasing time (i.e., that dephasing associated with the zero‐phonon line), T2*, is 6.4 ns at 5 K, the slowest dephasing time yet reported for a molecular glassy system at this temperature. At higher temperatures, dephasing due to exchange coupling with pseudolocalized modes at 50 and 180 cm−1, which correlate well with the transverse and longitudinal acoustic modes of water, becomes dominant. The exchange coupling mechanism is based on diagonal quadratic electron–phonon coupling. At 100 K, f...

Q-band splitting and relaxation of aluminum phthalocyanine tetrasulfonate

Abstract The doublet band structure evident in the fluorescence excitation and absorption spectra of aluminum phthalocyanine tetrasulfonate in various hyperquenched glassy solvents is attributed to splitting of the Q-band transition into x and y components. The splitting is caused by the ligation of water molecules to the aluminum atom which decreases the molecular symmetry. Picosecond relaxation from the Q y band to the Q x band is evident in the hole burned spectra.

New standard for high-temperature persistent-hole-burning molecular materials: aluminum phthalocyanine tetrasulphonate in buffered hyperquenched glassy films of water

Applications of persistent spectral hole burning to optical memory and processing technologies currently face a number of hurdles. Not the least important of these are efficient hole burning, high storage density in the frequency domain, resilience against destructive readout, and operation at high temperatures (⩾77 K). It is shown that aluminum phthalocyanine tetrasulphonate (APT) in buffered hyperquenched glassy water (HGW) is a material whose hole-burning properties exceed, in every category, those of previously studied molecular systems. Its attributes at 77 K include a frequency storage-density parameter (ratio of the inhomogeneous broadening to the homogeneous width of the zero-phonon line) of 125 (∼105 at 5 K), a burn fluence as low as 1.5 mJ/cm2 for production of a zero-phonon hole with a fractional depth of 0.1, and a quite impressive resilience against destructive readout from hole burning and light-induced hole filling. It was predicted, for APT in deuterated HGW, that ∼108 digital readouts could be executed before refresh was necessary. The mechanism for hole burning of APT in HGW is nonphotochemical, a one-photon process. The results argue against the notion that only two-photon gated hole-burning materials hold promise for memory/processing applications. Although HGW is not a practical host medium for devices, a biomolecular strategy for the design of materials that might be and that retain the exceptional hole-burning properties of APT in HGW is proposed. In this regard, the first demonstration of hole burning in Jello is presented.

A model for persistent hole burned spectra and hole growth kinetics that includes photoproduct absorption: Application to free base phthalocyanine in hyperquenched glassy ortho-dichlorobenzene at 5 K

Persistent nonphotochemical and photochemical hole burning of the S0→S1 origin absorption bands of chromophores in amorphous hosts such as glasses, polymers and proteins at low temperatures have been used to address a number of problems that range from structural disorder and configurational tunneling to excitation energy transfer and charge separation in photosynthetic complexes. Often the hole burned spectra are interfered by photoproduct (antihole) absorption. To date there has been no systematic approach to modeling hole burned spectra and the dispersive kinetics of zero-phonon hole growth that accounts for the antihole. A “master” equation that does so is presented. A key ingredient of the equation is a time-dependent, two-dimensional site excitation frequency distribution function (SDF) of the zero-phonon lines. Prior to hole burning (t=0) the SDF is that of the educt sites. For t>0 the SDF describes both educt and photoproduct sites and allows for burning of the latter that revert to the educt site...

Modeling of dispersive nonphotochemical hole growth kinetics data: Al-phthalocyanine tetrasulphonate in hyperquenched glassy water

Zero-phonon hole (ZPH) growth kinetics data that span six decades of burn fluence are reported for Al-phthalocyanine tetrasulphonate (APT) in hyperquenched glassy water (HGW) at 5.0 K. The kinetics are highly dispersive. The hole growth equation used for analysis of the dispersion incorporates three distributions (λ, α, and ω) where λ is the tunnel parameter associated with nonphotochemical hole burning (NPHB), α is the angle between the transition dipole and the laser polarization and the ω-distribution stems from off-resonant absorption of the zero-phonon line (ZPL). The single site absorption profile used includes the phonon sideband as well as the ZPL. The homogeneous width of the ZPL and shape of the phonon sideband were determined from experiment. Eight models, which include the possible combinations of the above distributions, were used to fit the data. As in previous works the λ-distribution was taken to be a Gaussian peaked at λ=λ0 with a standard deviation of σλ. The results show that the contri...

NONPHOTOCHEMICAL HOLE BURNING IN HYPERQUENCHED GLASSY FILMS OF WATER : A PRONOUNCED DEUTERATION EFFECT

The effects of deuteration on hole burning of aluminum phthalocyanine tetrasulfonate (APT) in glassy films of water is reported. Deuteration has no effect on the zero phonon hole width of the APT electronic transition, but a large effect on the hole burning kinetics. These effects are discussed in terms of the two level systems of glassy water.

Non-Lorentzian zero-phonon holes and new insights on nonphotochemical hole burning: Al-phthalocyanine in hyperquenched glassy water

Zero-phonon hole (ZPH) profiles and hole spectra that span about eight decades of burn fluence are reported for Al-phthalocyanine tetrasulphonate in hyperquenched glassy water (HGW) films at 5.0 K. The profiles of unsaturated zero-phonon holes (low burn fluence stage) are more sharply tipped than a Lorentzian. It is shown that the non-Lorentzian behavior is a natural consequence of the interplay between the three distributions that govern the dispersive kinetics of nonphotochemical hole growth. They are denoted by λ, α, and ω, where λ is the tunnel parameter associated with nonphotochemical hole burning (NPHB) and α is the angle between the transition dipole and the laser polarization. The ω distribution stems from off-resonant absorption of the zero-phonon line (ZPL). The single site absorption spectrum used in the calculations included the ZPL and the phonon sideband. The contribution of a distribution of homogeneous ZPL widths to the non-Lorentzian behavior was assessed and found to be negligible compa...

Laser-induced hole filling and spectral diffusion of aluminum phthalocyanine tetrasulfonate in hyperquenched glassy films

Laser-induced hole filling and spectral diffusion for the dye aluminum phthalocyanine tetrasulfonate in hyperquenched glassy films of water, ethanol, and methanol are investigated. Burning multiple holes into these films reveals a dependence on the burn direction, which is explained by the asymmetry of the antihole produced in the burning process. Spectral diffusion rates are shown to be dependent on sample annealing at temperatures well below the glass transition temperature, Tg. This is interpreted in terms of a β-relaxation process of the glass and is identified with transport of free volume.

Non-photochemical versus photochemical hole burning in hyperquenched glassy water and cubic ice

3The Shu-Small mechanism (J. Opt. Soc. Am. B 9 (1992) 724) for non-photochemical hole burning (NPHB) of electronic transitions of chromophores in amorphous hosts at low temperatures is based on a hierarchy of configurational tunneling events that begin in the outer shell and terminate in the inner shell that surrounds the chromophore. Connectivity between the intrinsic and extrinsic two level systems that stem from structural disorder and the excess free volume of glasses are key features of this mechanism. This mechanism has recently been modified to take into account multilevel extrinsic systems (J. Chem. Phys. 114 (2001) 9105). An important prediction of the Shu-Small mechanism is that NPHB should cease upon formation of a crystalline phase produced, for example, by warming of a vitrified glass. In this paper data are presented that are consistent with that prediction. The systems studied are aluminum phthalocyanine tetrasulphonate (APT) and free base phthalocyanine tetrasulphonate (PcT) in hyperquenched glassy films of water (HGW) and cubic ice (I c ). The hole-burning mechanisms for APT and PcT are non-photochemical and photochemical, respectively. Surprisingly, the hole-growth kinetics for PcT are as highly dispersive as are the kinetics for APT. This means that the kinetics for photoinduced proton tautomerization in PcT are strongly influenced by its nanoenvironment of water molecules, some of which are involved in H-bonding to the -NH groups of PcT.