Running title: Hybrids of thioalkyl-porphyrazines with nanocarbons
ABSTRACTWe designed a novel pyrene-substituted thioethyl-porphyrazine (PzPy) and the formation of supramolecular assembly with nanocarbons demonstrating photoinduced electron transfer ability. As revealed by spectroscopic and electrochemical studies, PzPy displays wide spectral absorption in the visible range, charge separation upon photoexcitation, as well as bandgap and highest occupied/lowest unoccupied molecular orbital (HOMO/LUMO) energy values, matching the key requirements of organic optoelectronic. Moreover, the presence of a pyrene moiety promotes attractive interactions with -conjugated systems. In particular, theoretical calculations show that in the PzPy the HOMO and LUMO are localized on different positions of the molecule, i.e., the HOMO on the pyrene moiety and the LUMO on the macrocycle. Therefore, HOMO-LUMO excitation gives rise to a charge separation, preventing excitons recombination. Two kinds of non-covalent hybrid composites are prepared by mixing the PzPy with single wall carbon nanotubes (SWNTs) and graphene nanoflakes (GNFs), respectively, and used for photocurrent generation through charge transfer processes between PzPy and nanocarbons. Photoconduction experiments show photocurrent generation upon visible light irradiation of both PzPy/SWNT and PzPy/GNF composites (0.78 and 0.71 mA/W at 500 nm, respectively), demonstrating their suitability for optoelectronic applications and light harvesting systems.widely used for this purpose. [12] More recently, carbon nanotubes (CNTs) have also been reported as acceptors, [13][14][15] and the use of graphene is rapidly raising too. [16][17][18][19][20][21] In particular, single wall carbon nanotubes (SWNTs) have been proposed as acceptor material since they possess nanoscale diameter and large aspect ratio in combination with favorable electrical transport properties. [14,19] Furthermore, SWNTs show unique optoelectronic properties, electrochemical stability, and energy levels that can be suitably coupled to those of conjugated polymers with long-range charge transport properties to make efficient composites for optoelectronic devices. [19] Similarly, graphene has high electron and hole mobility at room temperature, with reported values exceeding 15000 cm 2 V -1 s -1 . [20][21][22] Graphene is also electrochemically stable, with a very high specific surface area (∼ 2630 m 2 g −1 ), surpassing that of both SWNTs and graphite. [23,24] Moreover, graphene has an optical transmittance over the visible range of 97.7%, [25] and its work function (∼ 4.5 eV) [26] can be matched to the energy levels of organic donor materials. [22] Moving from these motivations, both SWNTs and functionalized graphene have been used as electron acceptors in combination with conjugated polymer donors, such as poly(3-octylthiophene) (P3OT), or poly(pphenylenevinylenes), and poly(3-hexylthiophene) (P3HT), [14,19,27,28] especially in organic bulk heterojunction (BHJ) solar cell devices. [19] Amongst the non-poly...