Solvent-Dependent Excited-State Evolution of Prodan Dyes

0549945 - ÚFCH JH 2022 RIV US eng J - Journal Article
Pospíšil, Petr - Cwiklik, Lukasz - Sýkora, Jan - Hof, Martin - Greetham, G. M. - Towrie, M. - Vlček, Antonín
Solvent-Dependent Excited-State Evolution of Prodan Dyes.
Journal of Physical Chemistry B. Roč. 125, č. 51 (2021), s. 13858-13867. ISSN 1520-6106. E-ISSN 1520-5207
R&D Projects: GA ČR(CZ) GA21-05180S
Institutional support: RVO:61388955
Keywords : Solvents * Quantum mechanics * Fluorescence
OECD category: Physical chemistry
Impact factor: 3.466, year: 2021
Method of publishing: Limited access

Excited-state character and dynamics of two 6-(dimethylamino)-2-acylnaphthalene dyes (Prodan and Badan-SCH2CH2OH) were studied by picosecond time-resolved IR spectroscopy (TRIR) in solvents of different polarity and relaxation times: hexane, CD3OD, and glycerol-d8. In all these solvents, near-UV excitation initially produced the same S1(ππ*) excited state characterized by a broad TRIR signal. A very fast decay (3, ∼100 ps) followed in hexane, whereas conversion to a distinct IR spectrum with a ν(C═O) band downshifted by 76 cm–1 occurred in polar/H-bonding solvents, slowing down on going from CD3OD (1, 23 ps) to glycerol-d8 (5.5, 51, 330 ps). The final relaxed excited state was assigned as planar Me2N → C═O intramolecular charge transfer S1(ICT) by comparing experimental and TDDFT-calculated spectra. TRIR conversion kinetics are comparable to those of early stages of multiexponential fluorescence decay and dynamic fluorescence red-shift. This work presents a strong evidence that Prodan-type dyes undergo solvation-driven charge separation in their S1 state, which is responsible for the dynamic fluorescence Stokes shift observed in polar/H-bonding solvents. The time evolution of the optically prepared S1(ππ*) state to the S1(ICT) final state reflects environment relaxation and solvation dynamics. This finding rationalizes the widespread use of Prodan-type dyes as probes of environment dynamics and polarity.
Permanent Link: http://hdl.handle.net/11104/0325840