Structure–Property Studies of Bichromophoric, PAH-Functionalized Dithieno[3,2-b:2′,3′-d]phospholes

Abstract

A series of dithienophospholes featuring polyaromatic hydrocarbon (PAH) substituents, with increasing number of fused rings ranging from 2 to 4 at the phosphorus center, have been synthesized and characterized. The installation of a large π-system in the vicinity of the dithienophosphole scaffold was found to induce unusual photophysics for this system that are based on the creation of two neighboring chromophores within the same molecular scaffold. Extensive photophysical studies revealed that significant energy transfer (ET) occurs from the PAH unit, which acts as a donor, to the dithienophosphole acceptor, showing ET efficiencies of almost 90%. TD-DFT calculations confirm the possibility for the two subunits to communicate with each other. Furthermore, due to the presence of the out-of-plane dithienophosphole unit, the PAH species do not show any significant tendency to form aggregates, such as excimers/exciplexes, even in colloidal suspensions.

Tunable Photochromism in the Robust Dithienylethene‐Containing Phospholes: Design, Synthesis, Characterization, Electrochemistry, Photophysics, and Photochromic Studies

“…Upon excitation into the transition band at about 308–382 nm of compounds 1 – 6 in degassed benzene solution at room temperature, the compounds display intense blue to greenish‐yellow luminescence at about 456–472 nm and the lifetimes of the compounds are found to be in the nanosecond range. The Stokes shifts of the compounds varied from 4765 to 5762 cm −1 9b. 20 Parallel to the electronic absorption study, the emission bands of the electron‐donating group‐substituted phosphole ( 4 ) and the electron‐withdrawing group‐substituted phospholes (compounds 1 and 2 ) occur at lower energy than that of the unsubstituted counterpart, as shown in Figure 6…”

P‐Terthienyl‐Functionalized Dithieno[3,2‐b:2′,3′‐d]phospholes

“…This 86 nm redshift suggests the presence of an intermolecular π–π interaction very likely due to the exposed linear terthienyl moiety that results in excimer emission at higher concentrations 19. It is important to mention that this type of behavior was not as pronounced, if observed at all, in related P ‐pyrenyl dithienophospholes,13a even though pyrene itself readily forms excimers20 at high concentrations. The blueshifted solid‐state emission of 4 relative to that as a solution in highly concentrated CH 2 Cl 2 can be attributed to the fact that formation of excimers in solution requires an appropriate intermolecular alignment of two species (possibly with different conformations) to aggregate,19 which may not be available in the solid state.…”

Structure–property studies of P-triarylamine-substituted dithieno[3,2-b:2′,3′-d]phospholes

“…29 In contrast, indolocarbazole-substituted 3e showed a slightly downeld-shied 31 P NMR resonance at d ¼ 22.2 ppm that is, however, in line with related systems exhibiting exocyclic polyaromatic hydrocarbon (PAH) substituents. 30 By contrast, ortho-derivative 3c featured a signicantly upeld-shied 31 P NMR chemical shi at d ¼ 12.9 ppm compared to its congeners 3a and 3b, indicating a distinctively different chemical environment of the phosphorus atom for this particular conguration. In all cases, the n-butyl substituents at the dithienophosphole core led to slightly (1-3 ppm) downeld-shied resonances, which is in accordance with previous ndings.…”

“…Nevertheless, interactions between the s*-orbital of the exocyclic bond and the p*-system of the ring lead to a certain degree of aromaticity and a high polarizability of the phosphole system. 23,24 The resulting high tunability of the photo-physical and electro-chemical properties by chemical modication 22,23,25 suggested the utility of this versatile building block for the elds of luminescent materials, [26][27][28][29][30][31] polymers, [32][33][34] coordination chemistry 26,35 and selforganizing materials. 36,37 In particular, oxidation of the phosphorus center is an appealing strategy to signicantly enhance the electron-accepting properties of the dithieno[3,2-b:2 0 ,3 0 -d] phosphole moiety, 21,24 which enables the application of this scaffold in donor-acceptor type materials.…”

“…Recently, the inuence of exocyclic donor groups on the properties of dithieno[3,2-b:2 0 ,3 0 -d]phosphole based donoracceptor materials has been investigated [29][30][31] revealing efficient charge transfer from the donor to the dithieno[3,2-b:2 0 ,3 0 -d] phosphole oxide core. 29 Herein we report on the synthesis and characterization of a new series of dithieno[3,2-b:2 0 ,3 0 -d] phosphole oxides with phenylcarbazole or indolo[3,2,1-jk] carbazole substituents as exocyclic donor moieties; the experimental results have been correlated with DFT calculations.…”