Photophysical and Redox Properties of Perylene Bis- and Tris-Dicarboximide Fluorophores with Triplet State Formation: Transient Absorption and Singlet Oxygen Sensitization

Abstract

A detailed photophysical characterization of a couple of new perylene imide derivatives, a carboxylic trisimide PIx, and an asymmetrically substituted carboxylic bisimide PIa is presented. PIx and PIa have the lowest singlet excited state just below 2.6 eV. The dyes are remarkably fluorescent (ϕ(f) = 0.37 ± 0.03 for PIa and ϕ(f) = 0.58 ± 0.04 for PIx in toluene), but they also display an efficient intersystem crossing. This leads to typical excited triplet photophysics/photochemistry, with intense triplet state absorption spectra and efficient singlet oxygen ((1)Δ(g)) photosensitization (ϕ(Δ) = 0.68 ± 0.02 for PIa and 0.44 ± 0.02 for PIx in toluene). On the basis of the measured ϕ(Δ), a ϕ(isc) of 0.65 ± 0.02 for PIa and 0.43 ± 0.02 for PIx in toluene is derived. PIx reduces at -0.58 eV vs SCE, almost similarly to the corresponding symmetrically substituted perylene bisimide PI0, but unlike the latter, it has the first oxidation potential above +1.9 V. PIa is more electron rich and displays a more difficult first reduction at -0.95 V with a more facile oxidation at +1.75 V, similar to that of the parent PI0. The absorption spectra of the excited singlet and triplet states and that of electrochemically generated monoanions are reported.

Phosphorescent perylene imides

“…The spectra from the two different apparatuses are in excellent agreement and show intense bands respectively at 686, 764 and 862 nm for PIa and 737, 830 and 948 nm for PIx. One can notice that the bands formerly detected above 900 nm 8 ( Fig. S1, ESIw) may represent only the weakest low energy tail of the phosphorescence.…”

“…1). 8 A remarkable feature of these new PIs is an intrinsic high triplet yield, an unprecedented feature for this class of compounds. Triplet reactivity for PIs has been formerly reported only as a consequence of inter-molecular 9 or intra-molecular sensitization [10][11][12] or under conditions of induced enhancement of triplet yield in multi-component arrays.…”

“…In fact a single broad band at around 950 nm could be detected and this casts doubts on the correctness of the previous assignment. 8 In the present study we intend to address in more detail the phosphorescence issue, to measure a reliable phosphorescence spectrum and derive the triplet excited state energy in order to fully characterize this state for the two compounds.…”

Photoinduced processes in a dyad made of a linear and an angular perylene bisimide

“…[7][8][9] This new perylene bisimide derivative is more electron rich than PI0, in addition to a still high fluorescence quantum yield (ϕ fl = 0.37 ± 0.03) PIa is able to undergo efficient intersystem crossing. Therefore, at variance with most perylene bisimides, it displays typical triplet state photoreactivity as singlet oxygen photosensitization 8 with ϕ Δ = 0.68 ± 0.02, and low temperature phosphorescence at 692 nm.…”

“…[7][8][9] This new perylene bisimide derivative is more electron rich than PI0, in addition to a still high fluorescence quantum yield (ϕ fl = 0.37 ± 0.03) PIa is able to undergo efficient intersystem crossing. Therefore, at variance with most perylene bisimides, it displays typical triplet state photoreactivity as singlet oxygen photosensitization 8 with ϕ Δ = 0.68 ± 0.02, and low temperature phosphorescence at 692 nm. 9 PIa has also been used as an electron donor in a dyad comprising corrole and has provided a charge separated state lifetime of several microseconds, an impressive result if one considers the simple structure of the array and the close proximity of the reactants.…”