John M. Hayes

Non-photochemical hole burning and impurity site relaxation processes in organic glasses

Abstract Laser-induced holes in the inhomogeneously broadened absorption spectra of aromatic hydrocarbons in frozen glasses are reported. The holes are shown to be of non-photochemical origin. Mechanisms for excited state site interconversion based on a metastable distribution of sites in asymmetric double well potentials are presented. Methods of eliminating non-photochemical holes and of distinguishing between photochemical and non-photochemical holes are described.

Theory for spectral hole burning of the primary electron donor state of photosynthetic reaction centers

A theory for solid state spectral hole burning is developed. The theory is valid for arbitrarily strong linear electron-phonon coupling within the Condon approximation which is accurate for strongly allowed optical transitions. Model calculations show that, from the dependence of the hole profile on the burn frequency, the contribution to the absorption linewidth from site inhomogeneity and the linear coupling parameters can be determined. The theory is used to analyze recent hole-burning data on the primary electron-donor states of isolated reaction centers of Rhodopseudomonas viridis, Rhodobacter sphaeroides and Photosystem I. The results show that all of these states are characterized by strong linear electron-phonon coupling (Huang-Rhys factor S ≳ 4) and large site inhomogeneous line broadening.

Red antenna states of photosystem I from cyanobacterium Synechococcus elongatus: a spectral hole burning study

Abstract The existence of at least three low-energy chlorophyll a (Chl a ) antenna states is shown for photosystem I (PS I) of Synechococcus elongatus by the use of nonphotochemical hole burning (NPHB) spectroscopy. In addition to the previously reported states at 708 and 719 nm, it is demonstrated that there is a third state at 715 nm. The responsible Chl a molecules are referred to as C-708, C-715 and C-719. For both Synechococcus and Synechocystis , the lowest energy state is shown to be characterized by strong electron–phonon coupling (large Huang-Rhys factor S ), large permanent dipole moment change ( f · Δμ ), and large linear pressure shift rates attributable to electron exchange of dimeric Chl a . The lowest energy state of Synechocystis is at 714 nm. The properties of the 714 and 719 nm states are very similar, suggesting that their dimer structures are also similar. Although the other red antenna states of these cyanobacteria have smaller values for S , f · Δμ , and linear pressure shift rate, these are still larger than typically measured for monomeric antenna Chl a . Possible assignments of red absorption bands to particular chlorophyll dimers or trimer are discussed.

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...

Mechanisms of non-photochemical hole-burning in organic glasses

Abstract From observation of the temperature dependence of hole formation and disappearance and of an anomalous temperature variation in zero-phonon fluorescence of tetracene in alcoholic glasses, conclusions regarding hole-burning mechanisms are made. At temperature above ≈10 K the homogeneous hole width allows determination of the rate of site interconversion.

Symmetry reduction–vibronically induced mode mixing in the S1 state of β‐methylnaphthalene

Supersonic jet excitation and single vibronic level (SVL) dispersed fluorescence spectra for α‐ and β‐methylnaphthalene (S1 state) are presented. Marked mirror symmetry breakdown between the excitation and origin excited fluorescence spectra of the β isomer is observed. The SVL spectra reveal that mode mixing in the S1 state is too extensive to be accounted for by first order treatment of the Duschinsky effect. Vibronically induced mode mixing in the β isomer is suggested as the mechanism which leads to intramolecular vibrational energy redistribution which onsets at a significantly lower excess vibrational energy than in naphthalene. The implications of our findings for other polyatomics are discussed.

Persistent hole burning of the primary donor state of photosystem i: strong linear electron-phonon coupling

Abstract Persistent photochemical hole burning for P-700 (primary donor state of photsystem I) for enriched reaction center particles is reported. Profiles consisting of a sharp zero-phonon hole superimposed on a very broad hole are interpreted in terms of strong linear electron-phonon coupling. The lifetime of P-700 at 1.6 K is ≈ 90 ps.

Vibronic activity in the laser jet spectra of phenanthrene

Abstract Photoexcitation and dispersed fluorescence spectra of phenanthrene and phenanthrene-d10 in supersonic expansions of helium are presented. Mirror symmetry breakdown (MSB) between excitation and S1 origin excited fluorescence is quantified for transitions involving planar vibrational modes. For modes which are totally symmetric, model calculations are performed based on the formalism of Craig and Small for the interference of Condon and Herzberg-Teller derived transition moments. It is shown that for a1 transitions displaying drastic absorption/fluorescence asymmetries, observed intensities can be reproduced by use of simple first-order formulae. The breakdown of the model in predicting the 2010 (632 cm−1 in S1) and 2001 (679 cm−1 in S0) transitions in phenanthrene-d10 is discussed. Mode mixing is observed in several b2 levels and in a1 levels near 1380 cm−1 in S1 and are described in terms of normal coordinate (Duschinsky) rotation and Fermi resonance, respectively.

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.