Phthalocyanines: An Old Dog Can Still Have New (Photo)Tricks!

Abstract

Phthalocyanines have enjoyed throughout the years the benefits of being exquisite compounds with many favorable properties arising from the straightforward and diverse possibilities of their structural modulation. Last decades appreciated a steady growth in applications for phthalocyanines, particularly those dependent on their great photophysical properties, now used in several cutting-edge technologies, particularly in photonic applications. Judging by the vivid reports currently provided by many researchers around the world, the spotlight remains assured. This review deals with the use of phthalocyanine molecules in innovative materials in photo-applications. Beyond a comprehensive view on the recent discoveries, a critical review of the most acclaimed/considered reports is the driving force, providing a brief and direct insight on the latest milestones in phthalocyanine photonic-based science.

Keywords: charge transfer; nonlinear optics; photocatalysis; photoelectronics; photonics; photovoltaics; phthalocyanine.

Figure 1

General structure of metal-free phthalocyanine (left) and metal phthalocyanine complex (right), with schematic representation of possible structural modulation sites and ring numbering.

Figure 2

Relative weight of reports retrieved using the term “phthalocyanin*” (orange bars) vs. its refining with the term “photo*” (blue bars). In parentheses are the percentage weights of photo-applications over all others.

Figure 3

Pcs used in photovoltaic ternary systems.

Figure 4

Representative cross-sectional image of a device based on phthalocyanine as HTM. Adapted with permission from ref [89]. Copyright 2017 Elsevier.

Figure 5

Pcs used in perovskite solar cells.

Figure 6

Cell performance and thermal stability. (a) J–V curves for the best cell using Pc 6 as HTM (in reverse (black) and forward (red) scans). The photovoltaic parameters of the best cell are shown in the inset table (average values in blue); (b) Stability of the devices tested at different temperatures (25, 85, 100, 115, and 130 °C, respectively) for 30 min, employing Pc 6 (black color), spiro-OMeTAD (red color), and PTAA (blue color); (c) Long-term stability of the devices stressed at 85 °C in air (25–30% humidity), using Pc 7 (black color) and spiro-OMeTAD (blue color) and 1100 h stability of the device utilizing Pc 6 at 85 °C in a nitrogen-filled glove box (red color); (d) J–V curves of a Pc 6 device before and after the thermal cycling test of 50 cycles within the temperature range between −40 °C and 85 °C. Adapted with permission from ref [92]. Copyright 2018 The Royal Society of Chemistry.

Figure 7

Phthalocyanines for application in semiconducting systems.

Figure 8

Energy-level diagram showing possible photochemical processes occurring in the Pc 16-MoS₂ hybrid material. Solid arrows show major processes; dashed arrows show minor ones. Adapted with permission from ref [118]. Copyright 2019 John Wiley and Sons.

Figure 9

Pcs used in photocatalysis.

Figure 10

(a) Operating set up based on the MOST concept; (b) Catalytic cycle for the back-reaction. Adapted with permission from ref [130]. Copyright 2019 The Royal Society of Chemistry.

Figure 11

Immobilized phthalocyanine photocatalysts for degradation of pollutants. Structure of compound 27 was adapted with permission from ref [136]. Copyright 2017 Elsevier.

Figure 12

Phthalocyanines for nonlinear optics applications.

Figure 13

Comparison in the electronic absorption spectra between Pcs 30 and 31, recorded in CHCl₃. Adapted with permission from ref [141]. Copyright 2016 American Chemical Society.

Figure 14

The nonlinear absorption and fitting curves (solid lines) of polymeric carboxyl phthalocyanines Z-scan (left: closed aperture; right: open aperture). Adapted with permission from ref [144]. Copyright 2017 American Chemical Society.

Figure 15

Phthalocyanine hybrid materials for NLO.

Figure 16

Transmittance of sandwich complexes and their conjugates with QDs depending on the incident fluence, performed at a pulse rate of 10 ns and I₀ ≈ 0.33 GW/cm². The red solid line corresponds to 50% transmittance (limiting threshold). Adapted with permission from ref [146]. Copyright 2017 John Wiley and Sons.