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Fig.5 (a) TGA spectra of ferrocenyl substituted DPPs 20-22 and 24; (b) fluorescence spectra of N-phenyl carbazole substituted DPPs 11-14 Reproduced from ref. 15 with permission from Wiley-VCH Verlag GmbH & Co. KGaA, Copyright 2016. In the context of improving the absorption of DPP, triphenyl- amine moieties were attached to DPP in symmetrical and unsymmetrical ways and the frontier energy levels suggested that molecules 1 and 2 can be used as electron donors for BH] OSCs (Chart 2). DPP 1 and 2 when used along with PC;,BM as an electron acceptor for OSCs showed PCEs of 2.23% and 3.05% respectively.*? Another donor carbazole was attached in place of the triphenylamine donor to DPP (11 and 12) and used as a donor along with the PC;,BM acceptor for BHJ-OSCs, exhibiting PCEs of 4.65% and 5.73% for 11 and 12 respectively.*° Further, thermally stable organometallic donor DPP has gained the attention of the research community due to its application as a fluorescent probe compared to other organic dyes. The DPP derivatives exhibit excellent photostability and high fluorescence quantum yield. But the functionalization of DPP with donors results in a decrease in the fluorescent nature. Moreover the functionalization with organometallic moi- eties such as ferrocene and cobalt dithiolene and incorporation of TCBD units completely quench the fluorescence. The fluores- cence spectra of N-phenyl carbazole substituted DPPs 11-14 are shown in Fig. 5b. The ethyne bridged DPPs (11 and 12) are fluorescent in nature but the TCBD derivatives (13 and 14) are non-fluorescent in nature. The quenching of fluorescence was observed due to self-absorption (overlap of the absorption and the emission spectrum) and quenching can also occur due to photoinduced charge transfer from the TCBD to the DPP moiety. The ethene and ethyne bridged di-substituted DPPs (28 and 29)

Figure 5 (a) TGA spectra of ferrocenyl substituted DPPs 20-22 and 24; (b) fluorescence spectra of N-phenyl carbazole substituted DPPs 11-14 Reproduced from ref. 15 with permission from Wiley-VCH Verlag GmbH & Co. KGaA, Copyright 2016. In the context of improving the absorption of DPP, triphenyl- amine moieties were attached to DPP in symmetrical and unsymmetrical ways and the frontier energy levels suggested that molecules 1 and 2 can be used as electron donors for BH] OSCs (Chart 2). DPP 1 and 2 when used along with PC;,BM as an electron acceptor for OSCs showed PCEs of 2.23% and 3.05% respectively.*? Another donor carbazole was attached in place of the triphenylamine donor to DPP (11 and 12) and used as a donor along with the PC;,BM acceptor for BHJ-OSCs, exhibiting PCEs of 4.65% and 5.73% for 11 and 12 respectively.*° Further, thermally stable organometallic donor DPP has gained the attention of the research community due to its application as a fluorescent probe compared to other organic dyes. The DPP derivatives exhibit excellent photostability and high fluorescence quantum yield. But the functionalization of DPP with donors results in a decrease in the fluorescent nature. Moreover the functionalization with organometallic moi- eties such as ferrocene and cobalt dithiolene and incorporation of TCBD units completely quench the fluorescence. The fluores- cence spectra of N-phenyl carbazole substituted DPPs 11-14 are shown in Fig. 5b. The ethyne bridged DPPs (11 and 12) are fluorescent in nature but the TCBD derivatives (13 and 14) are non-fluorescent in nature. The quenching of fluorescence was observed due to self-absorption (overlap of the absorption and the emission spectrum) and quenching can also occur due to photoinduced charge transfer from the TCBD to the DPP moiety. The ethene and ethyne bridged di-substituted DPPs (28 and 29)

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Department of Chemistry, Indian Institute of Technology Indore, Indore 453552, India. E-mail: rajneeshmisra@iiti.ac.in
Department of Chemistry, Indian Institute of Technology Indore, Indore 453552, India. E-mail: rajneeshmisra@iiti.ac.in
Chart 1 The chemical structures of DPP based small molecules 1-45,
Chart 1 The chemical structures of DPP based small molecules 1-45,
Scheme 1 General methodology used for the synthesis of DPP based small molecules 1-24. The general methodology used for the synthesis of donor functionalized DPPs and their TCBD derivatives 1-24 is shown The solution state electronic absorption spectra of alkylated thienyl DPP exhibit absorption bands in the range of 400 nm to 550 nm. The solid state absorption is red shifted compared to the solution state absorption due to intermolecular interactions
Scheme 1 General methodology used for the synthesis of DPP based small molecules 1-24. The general methodology used for the synthesis of donor functionalized DPPs and their TCBD derivatives 1-24 is shown The solution state electronic absorption spectra of alkylated thienyl DPP exhibit absorption bands in the range of 400 nm to 550 nm. The solid state absorption is red shifted compared to the solution state absorption due to intermolecular interactions
Fig. 1 Photograph of 11-14 in DCM (3 x 107° M). Reproduced from ref. 15 with permission from Wiley-VCH Verlag GmbH & Co. KGaA, Copyright 2016.
Fig. 1 Photograph of 11-14 in DCM (3 x 107° M). Reproduced from ref. 15 with permission from Wiley-VCH Verlag GmbH & Co. KGaA, Copyright 2016.
Fig. 2. (a) Normalized absorption spectra of 11-14; (b) cyclic voltammetry plots of 12 and 14. Reproduced from ref. 15 with permission from Wiley-VCH Verlag GmbH & Co. KGaA, Copyright 2016. Density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations supported the investi- gation of a red shift in the absorption with the lowering of the HOMO-LUMO gap after the incorporation of the TCBD unit into donor functionalized DPP. It also provided an idea about the localization of the electron density and the transitions in the absorption spectra. DFT investigation showed the stabilization DFT study revealed that the sp* hybrid N atom of triphenyl- amine breaks the electronic conjugation between the three arms,
Fig. 2. (a) Normalized absorption spectra of 11-14; (b) cyclic voltammetry plots of 12 and 14. Reproduced from ref. 15 with permission from Wiley-VCH Verlag GmbH & Co. KGaA, Copyright 2016. Density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations supported the investi- gation of a red shift in the absorption with the lowering of the HOMO-LUMO gap after the incorporation of the TCBD unit into donor functionalized DPP. It also provided an idea about the localization of the electron density and the transitions in the absorption spectra. DFT investigation showed the stabilization DFT study revealed that the sp* hybrid N atom of triphenyl- amine breaks the electronic conjugation between the three arms,
Fig. 3 (a) Normalized absorption spectra and (b) frontier molecular orbitals of DPPs 28 and 37. because of which tri-substituted DPP 37 shows a red shift of only 36 nm compared to a red shift of 68 nm observed after making the dimer with an ethene bridge between two DPP units 28. The breaking of the conjugation between the three arms can also be seen from the frontier molecular orbitals, which are shown in Fig. 3b. The electron density is localized all over the molecule in the HOMO as well as the LUMO in the case of DPP and dimer 28. On the other hand, in the case of tri-substituted DPP 37, the electron density is localized on all the three arms in the HOMO, and the LUMO is concentrated only on two arms, which are also separated from each other by the sp* hybridized N atom of triphenylamine. This indicated that the sp*® hybridized N atom of triphenylamine breaks the conjugation between the three arms in tri-substituted DPP 37. The TGA and DSC analysis of 34 exhibited only one melting peak at 227 °C indicating its high purity. The thermal decomposition temperature for 34 at 5% weight loss is 394 °C, which is higher than that of phenyl bridged dimers 30 (384 °C) and 31 (391 °C) due to the extended rigidity and larger molecular weight of the additional DPP moiety. The optical absorption spectra exhib- ited absorption maxima at 602, 573 and 555 nm for 30, 31 and 34 respectively. The electronic absorption spectrum of DPPs recorded in the thin film state was red shifted, and broadened compared to the absorption in solution. The optical band gap values for DPPs 30, 31 and 34 are 1.75, 1.82 and 1.95 eV respectively. The energy levels were calculated from the onset of oxidation and reduction potentials from cyclic voltammetry and the values of the HOMO/LUMO for 30, 31 and 34 are —5.16/ —3.52, —5.18/—3.65 and —5.22/—3.27.
Fig. 3 (a) Normalized absorption spectra and (b) frontier molecular orbitals of DPPs 28 and 37. because of which tri-substituted DPP 37 shows a red shift of only 36 nm compared to a red shift of 68 nm observed after making the dimer with an ethene bridge between two DPP units 28. The breaking of the conjugation between the three arms can also be seen from the frontier molecular orbitals, which are shown in Fig. 3b. The electron density is localized all over the molecule in the HOMO as well as the LUMO in the case of DPP and dimer 28. On the other hand, in the case of tri-substituted DPP 37, the electron density is localized on all the three arms in the HOMO, and the LUMO is concentrated only on two arms, which are also separated from each other by the sp* hybridized N atom of triphenylamine. This indicated that the sp*® hybridized N atom of triphenylamine breaks the conjugation between the three arms in tri-substituted DPP 37. The TGA and DSC analysis of 34 exhibited only one melting peak at 227 °C indicating its high purity. The thermal decomposition temperature for 34 at 5% weight loss is 394 °C, which is higher than that of phenyl bridged dimers 30 (384 °C) and 31 (391 °C) due to the extended rigidity and larger molecular weight of the additional DPP moiety. The optical absorption spectra exhib- ited absorption maxima at 602, 573 and 555 nm for 30, 31 and 34 respectively. The electronic absorption spectrum of DPPs recorded in the thin film state was red shifted, and broadened compared to the absorption in solution. The optical band gap values for DPPs 30, 31 and 34 are 1.75, 1.82 and 1.95 eV respectively. The energy levels were calculated from the onset of oxidation and reduction potentials from cyclic voltammetry and the values of the HOMO/LUMO for 30, 31 and 34 are —5.16/ —3.52, —5.18/—3.65 and —5.22/—3.27.
Fig. 4 (a) Normalized absorption spectra of 21 and 45; (b) frontier molecular orbitals of 45; (c) DPV curve for the reduction process of 45. Reproduced with permission from ref. 34, Copyright 2017, Elsevier.
Fig. 4 (a) Normalized absorption spectra of 21 and 45; (b) frontier molecular orbitals of 45; (c) DPV curve for the reduction process of 45. Reproduced with permission from ref. 34, Copyright 2017, Elsevier.
Chart 2. Chemical structures of DPP based donors used in solar cells.
Chart 2. Chemical structures of DPP based donors used in solar cells.
Chart 3 Chemical structures of DPP based donors used in solar cells.
Chart 3 Chemical structures of DPP based donors used in solar cells.
Chart 4 Chemical structures of DPP based non-fullerene acceptors and polymer donors used in OSCs.
Chart 4 Chemical structures of DPP based non-fullerene acceptors and polymer donors used in OSCs.
Chart 5 Triphenylamine and ferrocenyl functionalized DPPs for photo- thermal therapy.
Chart 5 Triphenylamine and ferrocenyl functionalized DPPs for photo- thermal therapy.
Related topics:
Organic ChemistryMaterials ChemistrySupramolecular ChemistryElectrochemistryOrganometallic ChemistryOrganic ElectronicsTime-dependent density functional theorySynthetic Organic ChemistryMaterial ChemistryOrganometallic Synthesis
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