Aleksander. Siemiarczuk

Bio: Aleksander. Siemiarczuk is an academic researcher. The author has contributed to research in topics: Absorption spectroscopy & Dimethylaniline. The author has an hindex of 1, co-authored 1 publications receiving 63 citations.

Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures

Abstract: 6. Rehybridization of the Acceptor (RICT) 3908 7. Planarization of the Molecule (PICT) 3909 III. Fluorescence Spectroscopy 3909 A. Solvent Effects and the Model Compounds 3909 1. Solvent Effects on the Spectra 3909 2. Steric Effects and Model Compounds 3911 3. Bandwidths 3913 4. Isoemissive Points 3914 B. Dipole Moments 3915 C. Radiative Rates and Transition Moments 3916 1. Quantum Yields and Radiationless Deactivation Processes 3916

Ultrafast Charge Transfer in Amino-Substituted Boron Dipyrromethene Dyes and Its Inhibition by Cation Complexation: A New Design Concept for Highly Sensitive Fluorescent Probes

Abstract: The photophysical behavior of a newly synthesized aza crown-substituted boron−dipyrromethene (BDP) dye and its dimethylamino analogue were investigated with steady-state and time-resolved fluorometry and compared to a reference compound. In solvents more polar than hexane, excitation of the dyes leads to a fast charge transfer from the locally excited (LE) state to a weakly emissive charge-transfer (CT) state. The donor-substituted compounds show dual emission from the LE and CT state, both fluorescence quantum yields being low. The rate constant of excited-state charge separation, calculated from the global analysis of time-resolved emission data, was determined to 1.6 × 1011 s-1 in 1,4-dioxane. The crowned compound forms 1:1-complexes with various alkali and alkaline-earth metal ions, which exist as two conformers in solution. In these complexes, coordination of the cation to the nitrogen donor atom of the crown inhibits the charge-transfer process, leading to a cation-dependent enhancement of the LE em...

Effect of the Solvent Environment on the Spectroscopic Properties and Dynamics of the Lowest Excited States of Carotenoids

Abstract: The spectroscopic properties and dynamics of the lowest excited singlet states of peridinin, fucoxanthin, neoxanthin, uriolide acetate, spheroidene, and spheroidenone in several different solvents have been studied by steady-state absorption and fast-transient optical spectroscopic techniques. Peridinin, fucoxanthin, uriolide acetate, and spheroidenone, which contain carbonyl functional groups in conjugation with the carbon−carbon π-electron system, display broader absorption spectral features and are affected more by the solvent environment than neoxanthin and spheroidene, which do not contain carbonyl functional groups. The possible sources of the spectral broadening are explored by examining the absorption spectra at 77 K in glassy solvents. Also, carotenoids which contain carbonyls have complex transient absorption spectra and show a pronounced dependence of the excited singlet state lifetime on the solvent environment. It is postulated that these effects are related to the presence of an intramolecul...

Excited state properties of peridinin: Observation of a solvent dependence of the lowest excited singlet state lifetime and spectral behavior unique among carotenoids

Abstract: The spectroscopic properties and dynamic behavior of peridinin in several different solvents were studied by steady-state absorption, fluorescence, and transient optical spectroscopy. The lifetime of the lowest excited singlet state of peridinin is found to be strongly dependent on solvent polarity and ranges from 7 ps in the strongly polar solvent trifluoroethanol to 172 ps in the nonpolar solvents cyclohexane and benzene. The lifetimes show no obvious correlation with solvent polarizability, and hydrogen bonding of the solvent molecules to peridinin is not an important factor in determining the dynamic behavior of the lowest excited singlet state. The wavelengths of emission maxima, the quantum yields of fluorescence, and the transient absorption spectra are also affected by the solvent environment. A model consistent with the data and supported by preliminary semiempirical calculations invokes the presence of a charge transfer state in the excited state manifold of peridinin to account for the observat...

Ultrafast charge transfer in excited electronic states and investigations into fundamental problems of exciplex chemistry: Our early studies and recent developments

Abstract: Among various excited state molecular interactions, photoinduced charge transfer (CT) and electron transfer (ET) are the most important fundamental ones underlying most problems in photophysical, photochemical and photobiological reaction processes. Among the excited state molecular interactions, the excited dipolar solute-polar solvent interactions are not typical CT or ET interactions. Nevertheless, this interaction is very important in the ultrafast ET reactions between donor (D) and acceptor (A) molecules, where the reaction rate is controlled by the solvent dynamics. When photoexcitation of solute molecule induces a large dipole moment in the excited solute in a polar solvent, one can observe a large fluorescence Stokes shift due to the solvation, for which the first quantitative theoretical formula was proposed and its experimental proof was given by Mataga et al. in 1955 [(a) N. Mataga, Y. Kaifu, M. Koizumi, Bull. Chem. Soc. Jpn. 28 (1955) 690; (b) N. Mataga, Y. Kaifu, M. Koizumi, Bull. Chem. Soc. Jpn. 29 (1956) 465.] and also by Lippert et al. [(a) E. Lippert, Z. Naturforsch. 109 (1955) 541; (b) E. Lippert, Ber. Bunsenges. Phys. Chem. 61 (1957) 962.] at the same time independently. Recent advances in the experimental methods for the measurement of time-resolved spectra with femtosecond (fs) laser spectroscopy have enabled us to reveal precise features of the dynamics of the fluorescence Stokes shift due to the ultrafast solvation of the large dipole moment induced by the photoexcitation. Of course, the problems of the excited state molecular interactions are not limited to the above-mentioned simple inter- and intramolecular photoinduced CT and ET reactions, including the solute–solvent interactions, but more complex cases can arise. Namely, the electronic structures of intermolecular exciplexes (EXs), of intramolecular EXs with non-rigid bridges between D and A groups, and of excited CT complexes appear to change due to solute–solvent interactions, a phenomenon that induces further geometrical structural changes, depending on the solvent polarities. This problem is very important for EX chemistry, i.e., for the elucidation of the mechanisms of photoinduced CT and subsequent chemical reactions in solutions and is closely related to the mechanisms of fluorescence quenching reactions in solution, which is a very important problem with a long history. We have started systematic investigations on EX chemistry, including this problem of the fundamental mechanisms of the fluorescence quenching reactions in solutions, during the period 1950–1970 and have carried out extensive work on the fundamental aspects of EX chemistry by means of nanosecond (ns), picosecond (ps), and fs laser spectroscopic studies and also some theoretical investigations [N. Mataga, M. Ottolenghi, in: R. Foster (Ed.), Molecular Association, vol. 2, Academic Press, London, 1979, p. 1; N. Mataga, Pure Appl. Chem. 56 (1984) 1255; J. R. Bolton, N. Mataga, G. McLendon (Eds.), Electron Transfer in Inorganic, Organic and Biological Systems, Advances in Chemistry Series, vol. 228, American Chemical Society, Washington, DC, 1991; N. Mataga, T. Okada, M. Masuhara (Eds.), Dynamics and Mechanisms of Photoinduced Electron Transfer and Related Phenomena, Elsevier, Amsterdam, 1992; N. Mataga, H. Miyasaka, Prog. React. Kinet. 19 (1994) 317; T. Kakitani, N. Matsuda, A. Yoshimori, N. Mataga, Prog. React. Kinet. 20 (1995) 347; N. Mataga, H. Miyasaka, Adv. Chem. Phys. 107 (1999) 431; N. Mataga, Pure Appl. Chem. 69 (1997) 729]. In this article, we discuss the results of our early studies on the fundamental aspects of EX chemistry and also those of our recent investigations, developing our early studies, under 15 different topical headings that are closely related to the most important essential problems of EX chemistry.