Tuning the Rainbow: Systematic Modulation of Donor–Acceptor Systems through Donor Substituents and Solvent

Abstract

A series of donor-acceptor compounds is reported in which the energy of the triarylamine donor is systematically tuned through para substitution with electron-donating methoxy and electron-withdrawing cyano groups. The acceptor units investigated are benzothiadiazole (btd), dipyridophenazine (dppz), and its [ReCl(CO)3(dppz)] complex. The effect of modulating donor energy on the electronic and photophysical properties is investigated using (1)H NMR spectroscopy, DFT calculations, electrochemistry, electronic absorption and emission spectroscopies, ground state and resonance Raman spectroscopy, and transient absorption spectroscopy. Qualitative correlations between the donor energy and the properties of interest are obtained using Hammett σ(+) constants. Methoxy and cyano groups are shown to destabilize and stabilize, respectively, the frontier molecular orbitals, with the HOMO affected more significantly than the LUMO, narrowing the HOMO-LUMO band gap as the substituent becomes more electron-donating-observable as a bathochromic shift in low-energy charge-transfer absorption bands. Charge-transfer emission bands are also dependent on the electron-donating/withdrawing nature of the substituent, and in combination with the highly solvatochromic nature of charge-transfer states, emission can be tuned to span the entire visible region.

Chromophore-Functionalized Phenanthro-diimine Ligands and Their Re(I) Complexes

“…These values correlate well with those obtained for donor–acceptor species with comparable linear dimensions. 75 , 78 …”

Synthesis and Optical Properties of Unsymmetrically Substituted Triarylamine Hexaazatrinaphthalenes

“…The electrochemical results show the relative energies of the redox acceptor and donor moieties . The electrochemical data are presented in Table , and cyclic voltammograms in Figure S3 in the Supporting Information.…”

pysisyphus: Exploring potential energy surfaces in ground and excited states

“…By adding such electron‐donating or withdrawing‐groups to the triphenylamine (TPA) moiety in a rhenium complex, Larsen reported the effective emission energy tuning from a short‐lived 1 ILCT state (intra‐ligand‐charge‐transfer). [ 89 ] In an effort to adjust the interaction of ILCT and metal‐to‐ligand‐charge‐transfer (MLCT) states in fac ‐[Re(L)(CO) 3 ( α ‐diimine)] n + , Shillito investigated the role of the ancillary ligand L. [ 90 ] The α ‐diimine ligand corresponds to 1,10‐phenanthroline with TPA appended in the 5 position (phen‐TPA). Recently, the effect of further modifying TPA in the phen‐TPA ligand by electron‐donating methoxy or electron‐withdrawing cyano groups on the photophysics of two rhenium and platinum complexes was analyzed by a combined experimental and computational study.…”