Photophysical and Protonation Time Resolved Studies of Donor–Acceptor Branched Systems With Pyridine Acceptors

Abstract

A comparative study of the photophysical properties of octupolar pyridyl-terminated triphenylamine molecule, with its quadrupolar and dipolar analogues by means of ambient and low temperature steady state spectroscopy and fs to ns time resolved fluorescence spectroscopy is reported. The push-pull molecules bear triphenylamine electron donating core, pyridine peripheral electron acceptors and acetylenic π-bridge. The samples were studied in solvents of varying polarity and also upon addition of small amounts of acetic acid to induce protonation of the pyridine group. All samples exhibit significant positive fluorescence solvatochromism as well as a relaxation of their excited state to a solvent relaxed Intramolecular Charge Transfer state on the ps timescale. For the octupolar compound, excited state relaxation occurs simultaneously with excitation energy hopping among the branches. The hopping time is solvent polarity controlled since it becomes slower as the polarity increases. The experimental hopping times are compared to those predicted by Förster and Fermi formulations. The samples are capable of emitting broadband light covering almost the whole visible spectrum by careful control of protonation. Energy transfer from the neutral towards the protonated species on the 1 ps timescale is revealed.

Tuning the Photophysical Properties of Push‐Pull Azaheterocyclic Chromophores by Protonation: A Brief Overview of a French‐Spanish‐Czech Project

“…Timeresolved emission studies performed on compounds 67-69 revealed an energy transfer from the neutral to the protonated species on the 1 ps time scale. [37] As expected, a substantial . Photographs were taken upon irradiation with a handheld UV-lamp (λ exc = 366 nm).…”

The effect of protonation on the excited state dynamics of pyrimidine chromophores

“…However, although white light emission upon protonation from chromophores containing azaheterocycles has been achieved and white organic light emitting diodes (WOLEDs) have been obtained using this strategy, the fundamental photophysical properties of these systems have been mainly studied by steady state spectroscopy while less attention has been given in their excited state dynamics. 62 Such a study is crucial towards understanding the nature of the interactions among the neutral and protonated species as well as among the solute and different acids.…”

“…Very recently, our groups has studied the effect of protonation with acetic acid on the optical properties of pyridine-based chromophores, revealing a quenching of the neutral species fluorescence which was accompanied by a decrease of their excited state lifetime. 62 In this work, the effect of protonation on the photophysical properties of two pyrimidine-based chromophores is addressed focusing on the excited state dynamics. For this reason time resolved fluorescence spectroscopy in the fs-ps and ps-ns timescales has been employed.…”

“…Note that excitation is made at 400 nm and thus, the neutral molecules are mainly excited in the time resolved experiments. Therefore, the fluorescence from the protonated species originates by an energy transfer mechanism 62. However, the decays become faster for CSA addition above 0.67 eq.…”

Effect of protonation on the photophysical properties of 4-substituted and 4,7-disubstituted quinazoline push-pull chromophores

“…The fluorescence dynamics on the fs-ps timescale were measured by a femtosecond timeresolved fluorescence method based on the upconversion technique. [52,53] The dynamics were measured under magic angle conditions and the samples were excited at 385 nm, which corresponds to the second harmonic of a Ti:Sapphire fs laser emitting 80 fs pulses at 770 nm. The samples were placed in a 1 mm path-length specific cell that was continuously rotated, and had an optical density below 0.1 at the excitation wavelength.…”