Dynamics of Two-Color Two-Photon Excited Fluorescence of p-Terphenyl: Determination and Analysis of the Molecular Parameters

Abstract

We present the experimental and theoretical study of the two-photon excited polarized fluorescence of p-terphenyl dissolved in cyclohexane/paraffin. The fluorescence was produced within a two-color two-photon (2C2P) excitation scheme utilizing simultaneous absorption of two femtosecond laser pulses at 400 nm and at 800 nm with the total excitation energy of 4.649 eV. The fluorescence was detected by a time correlated single photon counting (TCSPC) system with two detectors. Using different combinations of the absorbed photon polarizations we extracted seven time-dependent molecular parameters from experiment that contain all information on the dynamics of the three-photon process under study. The analysis of the obtained molecular parameter values was based on the ab initio calculations of the vertical excitation energies and transition matrix elements in p-terphenyl and allowed for determination of the whole structure of the two-photon absorption tensor, fluorescence lifetime, and the rotational correlation time. The obtained results imply that the fluorescence in the conditions of our experiment was governed mostly by the d(z) component of the fluorescence transition dipole moment that is parallel to the molecular long axis Z. The tensor was found to be symmetric. The two-photon excitation in p-terphenyl occurs simultaneously via two channels, one of them resulting in the population of the totally symmetric excited state and the other in the population of the nontotally symmetric excited state. Moreover, the energetically allowed pure electron transitions are dipole forbidden and become allowed by vibronic coupling.

Исследование скорости релаксации фотовозбужденных молекул индола интерферометрическим методом pump and probe с пикосекундным разрешением

“…Для исследования быстропротекающих процессов релаксации воз-бужденных состояний широко используются методы, основанные на времякорреляционной спектроскопии счета фотонов молекулярной флу-оресценции [4][5][6][7], а также на технике pump-probe [8]. Особенно высокое временное разрешение может быть достигнуто с помощью методов pump-probe, поскольку сегодня доступны лазеры, генерирующие им-пульсы фемтосекундной длительности, а временную задержку между возбуждающим и зондирующим импульсами можно сделать короче длительности импульса.…”

Two-color two-photon excited fluorescence of indole: Determination of wavelength-dependent molecular parameters

“…The experimental setup based on the 2C2P excitation scheme and the procedure of processing the experimental data used in the present study are described in detail elsewhere. 17,18 The scheme of the experimental setup is sketched in Fig. 1.…”

“…The use of femtosecond laser pulses in TPEF experiments makes it possible to track the evolution of the fluorescence from the anisotropic ensembles of excited molecules in the real time domain with high temporal resolution. 8,16 The Braunschweig group 8,9,17,18 has recently used the femtosecond 2C2P excitation scheme for detailed investigation of important UV fluorophores: p-terphenyl (PTP) 17 and 2-methyl-5-t-butylp-quaterphenyl (DMQ). 18 The complete set of molecular parameters has been determined from experiment in those studies which met the conditions of the complete polarization experiment.…”

“…This paper presents the study of indole at seven effective excitation wavelengths in the spectral region 268-294 nm using the theory and experimental setup developed in our previous studies. 15,17,18 Indole (C 8 H 7 N), the chromophore of the amino acid tryptophan, attracted much attention of theoretical and experimental groups all over the world during latest decades as an important fluorescent marker responsible for most of the UV absorption in proteins. 19 The indole excitation properties and fluorescence behavior in various media are governed by two close-lying lowest excited states conventionally noted as 1 L a and 1 L b .…”

“…In this paper, the TPEF polarization technique was used for obtaining detailed photodynamic information on indole dissolved in propylene glycol. Using the experimental procedure and method of the experimental data analysis developed in our previous papers, 15,17 we experimentally determined and analyzed seven molecular parameters M K (R,R ′ ), the two-photon polarization ratio Ω, and the components of the two-photon excitation tensor S Rγ containing important information on the principal tensor axes and the anisotropy of indole two-photon absorptivity. The results obtained are in perfect agreement with the analysis by Callis 29 who theoretically reconstructed the two-photon excitation tensors for 1 L a and 1 L b states.…”