Donor-acceptor substituted phenylethynyltriphenylenes – excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission

Abstract

SummarySeveral 2-(phenylethynyl)triphenylene derivatives bearing electron donor and acceptor substituents on the phenyl rings have been synthesized. The absorption and fluorescence emission properties of these molecules have been studied in solvents of different polarity. For a given derivative, solvent polarity had minimal effect on the absorption maxima. However, for a given solvent the absorption maxima red shifted with increasing conjugation of the substituent. The fluorescence emission of these derivatives was very sensitive to solvent polarity. In the presence of strongly electron withdrawing (–CN) and strongly electron donating (–NMe2) substituents large Stokes shifts (up to 130 nm, 7828 cm−1) were observed in DMSO. In the presence of carbonyl substituents (–COMe and –COPh), the largest Stokes shift (140 nm, 8163 cm−1) was observed in ethanol. Linear correlation was observed for the Stokes shifts in a Lippert–Mataga plot. Linear correlation of Stokes shift was also observed with E T(30) scale for protic and aprotic solvents but with different slopes. These results indicate that the fluorescence emission arises from excited state intramolecular charge transfer in these molecules where the triphenylene chromophore acts either as a donor or as an acceptor depending upon the nature of the substituent on the phenyl ring. HOMO–LUMO energy gaps have been estimated from the electrochemical and spectral data for these derivatives. The HOMO and LUMO surfaces were obtained from DFT calculations.

Lanthanide(III) Complexes of Diethylenetriaminepentaacetic Acid (DTPA)–Bisamide Derivatives as Potential Agents for Bimodal (Optical/Magnetic Resonance) Imaging

“…These represent the well‐known S 0 → S 2 transitions of naphthalene‐based ligands 26. Finally, for Gd–DTPA–BEthA, a maximum absorption can be seen at 263 nm, which corresponds to the phenylethynyl group of the ligand 27…”

Optical sensing of aqueous boron based on polymeric hydroxytriphenylene derivatives

“…The emission maximum in DMF is independent of the substituents, indicating no signicant intramolecular charge transfer in the excited state. 33,34 However, in the case of 7a a small broad peak is visible around 550 nm, possibly due to interactions between the PEG chains and the free hydroxyl groups of the triphenylene moiety, leading to aggregation or excimer formation.…”

Spectral Characteristics of Highly Fluorescent 2-(<i>N,N</i>-dimethylamino)tryptanthrin

“…Equation (1) describes the Stokes shifts (=A -F) in terms of the change in dipole moment of the fluorophore (Δ = E -G) and the dependence of the dipole energy on the  values and refractive index (n) of the solvent. It also accounts for the general solvent effect, but it does not account for specific solvent-fluorophore interactions, such as those involved in hydrogen bonding [15]. The Lippert-Mataga plots for T2NH2 and T2NMe2 in aprotic solvents are shown in Figure 4.…”

“…The Lippert-Mataga plots for T2NH2 and T2NMe2 in aprotic solvents are shown in Figure 4. From the slopes in this plot, the change in the dipole moment (Δ) of the fluorophore upon electronic excitation (E -G) was estimated, assuming the molecular radius as the cavity radius [15]. The molecules under consideration are non-spherical; hence, the substitution of the molecular radius for the cavity radius is only approximate.…”