Decoupling Fluorescence and Photochromism in Bifunctional Azo Derivatives for Bulk Emissive Structures

Abstract

Bifunctional molecules that combine independent push-pull fluorophores and azo photochromes have been synthesized to create fluorescent structures upon light-induced migration in neat thin films. Their photochromic and emissive properties have been systematically investigated and interpreted in light of those of the corresponding model compounds. Fluorescence lifetimes and photoisomerization and fluorescence quantum yields have been determined in toluene solution. Kinetic analyses of the femtosecond transient absorption spectra reveal that the fluorophores evolve in a few picoseconds into a distorted intramolecular charge-transfer excited state, strongly stabilized in energy. Radiative relaxation to the ground state occurred competitively with the energy-transfer process to the azo moiety. Introduction of a 10 Å-long rigid and nonconjugated bridge between the photoactive units efficiently inhibits the energy transfer while it imparts enhanced free volume, which favors photoactivated molecular migration in the solid state.

Strong Color Tuning of Self‐Assembled Azo‐Derived Phosphonic Acids upon Hydrogen Bonding

“…In solvents like tetrahydrofuran (THF), dimethylformamide (DMF), ethyl acetate (AcOEt) or methanol, the solutions appeared orange with a band centered at 436–439 nm as commonly reported for azo derivatives due to ππ* charge transfer transitions involving the aminophenylazo unit (Figure a, Figure S1), and confirmed by TDDFT calculations at a B3LYP/6‐31G++(2d, 2p) level in THF to account for non‐covalent H‐bond interactions of AzoHBP with the solvent molecules (Figure S2). The second higher‐energy band located in the UV range around 330–340 nm can be ascribed to intramolecular charge transfer within the biphenylamino branches by analogy with previous compounds …”

“…The second higherenergy band located in the UV range around 330-340 nm can be ascribed to intramolecular charget ransfer within the biphenylaminob ranches by analogy with previous compounds. [19] When using toluene, AzoHBP hardly dissolved at early times. In the course of time, the solution turned bright orange and UV/Vis absorption spectroscopy revealed the rise of two bands at 341 and 431 nm ( Figure S3 a).…”

Nanosecond photochromic molecular switching of a biphenyl-bridged imidazole dimer revealed by wide range transient absorption spectroscopy

“…We set the excitation wavelength to 305 nm for ns and 310 nm for fs transient absorption measurements. The details of the experimental setup were reported previously 29,30 and are briefly shown in the ESI. † Fig.…”

Exploiting Light Interferences to Generate Micrometer‐High Superstructures from Monomeric Azo Materials with Extensive Orientational Mobility

“…Such a film thickness allowed for reduced adhesion effects of the azo layer with the glass substrate known to impair photomigration, [ 17 ] and yielded absorbance around 0.5, allowing for illumination throughout the azo thin films and not only by the upper surface. The fact that both E and Z isomers closely absorb [ 34 ] makes the photomigration more efficient since both isomers could be excited at 488 nm, near their absorption maximum. Under structured polarized light irradiation, push–pull azo materials undergo considerable mass transport according to mechanisms that keep being debated between optical, [ 35 ] entropy‐driven elastic, [ 36 ] or mechanical effects, [ 37 ] to form surface relief gratings (SRGs).…”