Strong Photophysical Diversity and the Role of Charge Transfer Excitons in Transition Metal Phthalocyanine β-Phases

Abstract

The photophysics of the three transition metal phthalocyanines NiPc, CuPc and ZnPc in their β-phase has been studied using complementary experimental techniques: photoluminescence, optical absorption and electronenergy-loss spectroscopy. We demonstrate that the strongly different photoluminescence signal can be understood based on the different exciton dispersions, and that tiny differences in the structure and thus the intermolecular orbital overlap is able to model these differences. Our results clearly indicate a significant admixture of charge-transfer excitations to the lowest exciton state. They additionally demonstrate the need of a detailed microscopic understanding of organic semiconductors for their application potential.

Symmetry-breaking charge transfer and intersystem crossing in copper phthalocyanine thin films

“…The presence of such an intermolecular charge-transfer state coupled to the intramolecular Frenkel excitons has been identified in both α-CuPc and β-CuPc. 36,40,42,79–81 The spectral lineshape for the β-CuPc steady-state absorption can therefore be similarly explained, with the predominant peaks at 640 and 725 nm being assigned to the first and second π–π* transitions on the phthalocyanine macrocycle, and lower intensity shoulders contributing due to the four-fold (F1, F2)-CT mixing. In the following, we explore how this mixing mediates photophysical dynamics in α- and β-CuPc.…”

“…Frenkel–CT mixing has been observed in various π-stacked organic chromophore systems, including pentacene, 21,24–27 perylene derivatives, 28–33 squaraines, 34,35 and also in phthalocyanines. 7,36–44 This mixing has been purported to influence photophysical mechanisms, such as singlet fission and the formation of free charge carriers via symmetry-breaking charge separation. 26,37…”

“…Frenkel-CT mixing has been observed in various p-stacked organic chromophore systems, including pentacene, 21,[24][25][26][27] perylene derivatives, [28][29][30][31][32][33] squaraines, 34,35 and also in phthalocyanines. 7,[36][37][38][39][40][41][42][43][44] This mixing has been purported to influence photophysical mechanisms, such as singlet fission and the formation of free charge carriers via symmetrybreaking charge separation. 26,37 Copper phthalocyanine (CuPc) is a robust small molecule OSC which, along with related derivatives, has attracted attention for a variety of applications.…”

Carbon Quantum Dot Conjugated Copper(II) Phthalocyanine Integrating BiVO4 Semiconductor for Photocatalytic Water Oxidation

“…The corresponding Copper(II) phthalocyanine (CuPc) is a ring compound with macrocyclic electron-conjugated structure, whose ball-and-stick model is shown in Figure S8. CuPc is very stable in concentrated acid and base and at high temperature, 47 whereas CuPc will decompose in hot nitric acid. 48 Here, we investigate the impact of CQDs on the stability of CuPc through controlled variable experiments.…”

Momentum Dependence of the Electronic Excitations in Polyfluorinated Metal Phthalocyanines

“…On the other hand, the thin film absorption results in rather broad spectra, which consist of at least four to five excitations, visible as maxima and shoulders, like the absorption spectra of the unfluorinated counterparts. 33,45 Moreover, the lowest excitation is shifted toward lower energies in the solid state, as a reason for solid-state effects. 46−48 These effects include the lifting of the degeneracy as a consequence of the symmetry reduction of the molecules in the crystal.…”