Optical and photophysical properties of anisole- and cyanobenzene-substituted perylene diimides

Abstract

One- and two-photon absorption cross-sections and spectra and the photophysical properties of eight perylenetetracarboxy-3,4:9,10-diimide (PDI) derivatives are reported and analyzed. The investigated compounds are characterized by direct binding of the phenyl rings of the substituents to the bay positions of the perylene core. They have been designed to test the effects of differences in the electronic nature - electron donating (anisole) or accepting (cyanobenzene) - and binding topology (cis or trans, meta or para disubstitution or tetrasubstitution) of the bay substituents on the above optical and photophysical observables. (TD)DFT and Hückel MO calculations have provided theoretical information on the ground-state geometries, the MOs and the electronic spectra of several model compounds. For tetrasubstituted and cis disubstituted derivatives, strong steric interactions in the bay area determined the preferred conformations, with perylene cores distorted near the substituted bay(s) and a 42-44° twisting of the substituent rings relative to the core, quite irrespective of the electronic nature of the substituents. On the other hand, in trans-disubstituted PDI steric hindrance in the bay areas was much weaker and similar in the cyanobenzene and the anisole derivatives. So, the large differences found in the conformational preferences were completely attributable to electronic effects. With electron-accepting cyanobenzene, the substituent rings were found normal to the central planar perylene core, thus enabling the assignment of the moderate spectroscopic effects to inductive interactions. The DFT analysis of the PDI trans-disubstituted with electron-donating anisoles gave quite strongly distorted perylene-core geometries and less twisted (59°) substituent rings. The corresponding increased substituent/core conjugative interactions resulted in new CT allowed electronic transitions and an extremely pronounced solvent-polarity dependence of the emission spectra and intensities. All anisole substituted PDI feature a very fast radiationless decay path in polar solvents, likely related to a relaxation to a charge-separated configuration in the lowest excited-state.

Synthesis and Self‐Assembly of Bay‐Substituted Perylene Diimide Gemini‐Type Surfactants as Off‐On Fluorescent Probes for Lipid Bilayers

“…The latter effect is generally attributed to an out‐of‐plane distortion of the perylene ring system because of the sterically encumbered substituent groups 65, 66. The overall bathochromic shift of the maximum absorption wavelength is due to the π‐donating effect of the oxygen substituents on the perylene ring system 52. The fluorescence spectra of 1,12‐bay‐substituted PDIs are a mirror image of their corresponding absorption spectra (Figure 3 a), including the loss of vibronic fine structure accompanied by a relatively large Stokes shift as compared with PDI 1 .…”

“…[65,66] The overall bathochromic shift of the maximum absorption wavelength is due to the p-donating effect of the oxygen substituents on the perylener ing system. [52] The fluorescence spectra of 1,12-bay-substituted PDIs are am irror image of their corresponding absorption spectra (Figure 3a), Figure 2. A) Expansion of the aromatic region of the 2D 1 H, 13 CHMBCs pectrum of PDI 3.The inset showsthe molecular structure of PDI 3 with the assigned protons and carbons.…”

“…Partly substituted 1,6‐ and 1,7‐regioisomers, commonly as mixtures,44, 45, 46, 47, 48 have also been synthesised,49, 50 while 1,12‐bay‐substituted PDIs have been rarely reported. The latter are interesting because the distortion of the perylene ring system by the 1,12‐substitution will strongly alter the optical properties of the compound, comparable to their corresponding tetrasubstituted PDIs, while solubility and self‐assembly properties will be different 51, 52, 53. Unfortunately, 1,12‐bay‐substituted PDIs have to be accessed through halogenation/dehalogenation chemistry,54, 55, 56, 57 which is typically inefficient, cumbersome, and low yielding.…”

“…The latter are interesting because the distortion of the perylene ring system by the 1,12-substitution will strongly alter the optical properties of the compound, comparable to their corresponding tetrasubstituted PDIs, while solubility and self-assembly properties will be different. [51][52][53] Unfortunately,1 ,12-bay-substituted PDIs have to be accessed through halogenation/dehalogenation chemistry, [54][55][56][57] which is typically inefficient, cumbersome, and low yielding. Controlled and efficient access to 1,12-bay-substituted PDIs is evidently challenging, and yet also potentially highly valuableg iven their untapped chemical potentiala nd prospective influence on the PDIs optical properties.…”

Perylenetetracarboxy-3,4:9,10-diimide derivatives with large two-photon absorption activity

“…These molecules have 2,6diisopropylphenyl groups at the imide positions and the derivative with four p-methoxyphenyl as bay substituents has a cross section of 180 GM at 850 nm, one order of magnitude greater respect to the reference derivative with no substituents in the bay positions. 46 It was also shown that tetrasubstitution causes twisting of the perylene core because of the steric hindrance between the phenyl rings connected at the bay positions. Another way of bay substitution involves the use of an ether linker between the perylene core and the -delocalized groups.…”