π-Extended diketopyrrolopyrrole–porphyrin arrays: one- and two-photon photophysical investigations and theoretical studies

Abstract

A complete one- and two-photon spectroscopic and photophysical characterization of three diketopyrrolopyrrole (DPP)-porphyrin conjugates is reported. The increased conjugation introduced by the incremental addition of one, two and four DPP units on the meso porphyrin positions strongly affects the optical properties of the systems. Ground and triplet excited state absorption spectra show a gradual broadening and bathochromic shift and a trend to lower energies is also observed for both fluorescence and phosphorescence emission. Interestingly, the fluorescence quantum yield increases along the series, leading to remarkable NIR emission properties for the larger derivatives. Unlike the model porphyrin, all derivatives exhibit high two-photon absorption activity. An increase in two-photon absorption cross-section in the regions 800-840 nm and 910-930 nm is observed moving from one DPP to two DPP appended units, with a value of the order of 4000 GM at 910 nm for the latter system. The four compounds show high efficiency in generating singlet oxygen, with yields ranging from 0.7 to 0.5, envisaging favourable applications in both one- and two-photon photodynamic therapies. A detailed theoretical exploration of both linear (absorption and emission) and non-linear (two-photon absorption) properties proposes an analysis of the experimental spectra and a comprehensive interpretation of the two-photon activity within the series of compounds.

Review of porphyrin-based photodynamic therapy materials

“…Porphyrins are a class of tetrapyrrole compounds, which consist of a planar porphin core surrounded by substituent groups [1][2][3]. It is undoubted and well documented that porphyrins are one of invaluable and ubiquitous molecular species, which play critical roles in living systems including photosynthesis [4][5][6][7].…”

Synthesis, Structure, Photophysics, and Singlet Oxygen Sensitization by a Platinum(II) Complex of Meso‐Tetra‐Acenaphthyl Porphyrin

“…[44] Porphyrins having increased conjugation at the β positions, often called π-extended porphyrins, have attracted significant attention as potential candidates for optoelectronic materials. [45] These compounds exhibited phosphorescence in the red-near infrared (NIR) region of the spectrum. [46] However, similar studies with the increased conjugation at the meso-phenyl ring have not been covered that much.…”

The Synthesis and Photophysical Properties of Weakly Coupled Diketopyrrolopyrroles

“…Looking for chromophores, which possess the suitable architecture for probing via weakening of their intramolecular electronic coupling, we focused on diketopyrrolopyrrole (DPP) derivatives ( Figure 1 ) [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. These donor–acceptor cross-conjugated dyes with DPP cores are characterized by straightforward synthesis [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ], almost a unity emission quantum yield [ 21 ], large two-photon absorption cross-section [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ], and broad utility in organic optoelectronics [ 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , …”

“…30 to ~7 degrees, thus altering the photophysical properties [ 21 ]. In particular, a bathochromic shift of absorption is often observed [ 79 , 80 , 81 , 82 ], accompanied by better packing in the crystalline state, stronger charge transfer, and larger two-photon absorption cross-sections [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ]. It is, therefore, interesting to study multiple architecture based on the DPP scaffold-possessing groups such as benzoxazole and benzothiazole either directly linked via benzene ring or elongated via thiophene rings.…”