Intramolecular Charge Transfer Properties Research Articles

Exploring the relationship between the “ON-OFF” mechanism of fluorescent probes and intramolecular charge transfer properties

In this study, the excited state charge distribution characteristics and fluorescence mechanism of HClO detection probes HN-ClO (weak fluorescence) and HN-ClO-F (strong fluorescence) probes were investigated based on density functional theory (DFT) and time-dependent density functional theory (TDDFT). The results of electrostatic potential (ESP) map and hole-electron analysis show that the HN-ClO and HN-ClO-F probes have obvious charge separation characteristics in the excited state. The excited state energy decomposition and Merz-Kollman charge analysis demonstrate the existence of distinct planar intramolecular charge transfer (PICT) features in HN-ClO and HN-ClO-F. Due to the strong charge coupling caused by the planar structure, the fluorescence of HN-ClO-F could occur. Furthermore, the weak fluorescence of HN-ClO is caused by inter-system crossing (ISC) between S1 and T1 state. Our result proves that the ICT process could exist in HN-ClO-F, but the PICT process does not cause fluorescence quenching, which have provided an excellent supplement to the mechanism of fluorescent probes. The conclusion is consistent with the fluorescence phenomenon observed in the experiment.

Photophysical and Electrochemical Properties of Highly π-Conjugated Bipolar Carbazole-1,3,4-Oxadiazole-based D-π-A Type of Efficient Deep Blue Fluorescent Dye.

In this contribution, we have designed and synthesized a novel carbazole-1,3,4-oxadiazole based bipolar fluorophore (E)-2-(4-(4-(9H-carbazol-9-yl)styryl)phenyl)-5-(4-(tertbutyl) phenyl)-1,3,4-oxadiazole (CBZ-OXA-IV). Wittig reaction is utilised for the synthesis of the designed bipolar target compound CBZ-OXA-IV. 1H NMR, 13C NMR, FT-IR and ESI-MS results confirmed the designed chemical structure of the fluorophore CBZ-OXA-IV. The photophysical properties have been investigated in detail using UV-Vis absorption, photoluminescence spectroscopy. Also, the photoluminescence studies on solid state samples (as thin films) were carried out. The CBZ-OXA-IV dye emits intense deep blue fluorescence with observed absorption and emission maxima occurring are at 353nm and 470nm, respectively. Fluorophore CBZ-OXA-IV has shown high Stokes shift of 7052cm-1. The experimentally measured optical band gap ([Formula: see text]) value is found to be 3.01eV and the fluorescence quantum yields (Φf) is 0.40. The intramolecular charge transfer property of CBZ-OXA-IV dye was examined by using photophysical properties such as absorption, emission in different solvents of different varying polarities. In addition, Density Functional Theory computations are studied in detail including the MEP surface plots and natural bond orbital analysis. The electrochemical properties have been investigated in detail by using cyclic voltammetry measurements. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurement results display a high thermal stability with decomposition temperature (Td5%) 387°C and a large glass transition temperature (Tg) of 98°C. The obtained results demonstrated that the novel bipolar fluorophore CBZ-OXA-IV could play an important role in organic optoelectronics and possibly can be utilized as bipolar transport materials for electroluminescence applications in optoelectronic devices/OLEDs.

Olefin-linked conjugated fluorescent oligomer: Design, synthesis, photophysical studies and detection of nitroaromatic compounds (NACs) in aqueous media

The development of novel fluorescent polymers has attracted significant attention owing to their potential applications in energy and environmental sciences. This study reports novel oligomer (TRZBT) synthesis via Wittig-Horner reaction using bithiophene aldehyde and triazine triethyl phosphite. The resulting oligomer possesses large porous morphology, which was confirmed using SEM analysis. Further, the chemical structure of TRZBT was confirmed by FT-IR, NMR, and GPC studies. The triazine acceptor (A) unit linked with bithiophene donor (D) unit through olefin π-conjugation resulted in a Donor-π-Acceptor (D-π-A) type oligomer. Detailed studies of the solvent-dependent photophysical properties of TRZBT were performed. Due to the alternate d-A structure of oligomer, enhanced intramolecular charge transfer (ICT) properties between D and A moiety was observed. Further, TRZBT in THF and THF: H2O (10:90) system effectively detected nitro-explosives in aqueous media, which exhibited high sensitivity, selectivity, and quick response via fluorescence quenching. TRZBT showed a higher quenching constant (Ksv) value of 4.91 × 105 M−1 towards picric acid as compared with other nitroaromatics. Significantly, the detection limit of 1.58 nM in a 100 % aqueous medium confirms that the synthesized material can detect even trace levels of the analyte.

Radical Photopolymerization Using 1,4-Dihydropyrrolo[3,2-b]pyrrole Derivatives Prepared via One-Pot Synthesis.

Radical photopolymerization has attracted significant attention for manufacturing products with complicated structures. Herein, the synthesized 1,4-bis(4-bromophenyl)-2,5-bis(4-nitrophenyl)-1,4-dihydropyrrole[3,2-b]pyrrole (PyBN) is found to show varying photoactivity upon irradiation at different wavelengths. PyBN affords two main absorption bands, and its maximum absorption peak is at 462 nm, attributing to its strong intramolecular charge transfer property based on the donor–acceptor structure. It efficiently photoinitiates the radical photopolymerization of different (meth)acrylate materials under 365 and 395 nm LED irradiation. The highest double bond conversion of 99.86% is achieved for these materials. Under 470 nm LED, PyBN does not show molecular structure change from photolysis results as a result of intramolecular charge transfer. Therefore, PyBN shows wavelength-selective photoactivity with potential application in dual-wavelength volumetric additive manufacturing. A unique solid product is successfully fabricated using a 365 nm LED with co-irradiation of a 470 nm LED. Additionally, PyBN incorporating camphorquinone (CQ) as a two-component visible light photoinitiator system is investigated under 470 nm LED irradiation. As PyBN has a charge transfer activity at 470 nm, the combination with CQ exhibits a good synergistic interaction. Besides nitro-based PyBN, a methyl-based PyBC was prepared as a reference compound.

New benzotriazole-based D–A–D type solvatochromic dyes for water content detection in organic solvents

Two new D-A-D structured organic dyes (LM1 and LM2) based on methoxy substituted triphenylamine (MeO-TPA) as the electron donor, N-aryl benzotriazole as the electron acceptor have been designed and synthesized for water content detection in organic solvents. Both dyes exhibit large stoke shift with solvatochromic properties and display apparent fluorescence quenching upon the addition of different amount of water in organic solvents. Compared to LM1, LM2 with stronger electron-withdrawing acceptor fluorinated benzotriazole possesses red-shifted absorption and fluorescence emission, enhanced intramolecular charge transfer (ICT) properties and stronger hydrogen-bonding interaction, resulting in a lower limit of detection (LOD) for water. The LODs in THF and 1,4-dioxane of LM2 are 0.009 % and 0.024 %, respectively, which indicates its great potential application in detecting water content in organic solvents.

Dual-Phase Emission AIEgen with ICT Properties for VOC Chromic Sensing.

In a film-based fluorescence sensor, luminogens are of vital importance since they play the role of probes or indicators. Traditional organic luminogens like pyrene show high luminescence quantum yields in dilute solutions, but their applications are usually limited by the aggregation-caused quenching (ACQ) effect and bad photochemical stability. Thus, this paper reports a novel aggregation-induced emission luminogen (AIEgen) containing both pyrene and o-carborane (CB-PY), which possesses unique dual-phase emission both in solution and solid state and intramolecular charge transfer (ICT) properties, fulfilling the gap between ACQ and AIE compounds. Importantly, the fluorophore presents extraordinary stability that there was almost no attenuation in the emission intensity of CB-PY in the solid state after 4 months of exposure at ambient conditions. It is these merits that make CB-PY exhibit outstanding sensing performances for volatile organic compounds (VOCs), where the fluorescence test strip shows fast, reversible, and visual discrimination of four organic solvents with varied polarities. Moreover, 92#, 95#, and 98# gasolines could be discriminated with CB-PY, showing different colors under UV illumination.

Carbazole-based D-π-A molecules: Determining the photophysical properties and comparing ICT effects of π-spacer and acceptor groups

4-(9′-Hexylcarbazol-3′-yl)benzaldehyde (Cz-Ph-CHO: 4) and 4-(9′-hexylcarbazol-3′-yl)benzylidenemalononitrile (Cz-Ph-CN: 5) were synthesised with the structure of D-π-A, where carbazole, phenylene and formyl/dicyanovinyl groups act as electron donor (D), pi-spacer (π) and electron acceptor (A) units, respectively. The thermal, electrochemical, optical and intramolecular charge transfer (ICT) properties of compounds 4 and 5 were investigated. Compounds 4 and 5, in particular their ICT behaviour, were also compared with the closely related structure, 2-(9′-hexylcarbazol-3′-yl)-5-pyridinecarbaldehyde (Cz-Py-CHO: 7). For the purpose of tuning chemical structure to obtain targeted properties, electrochemical data and absorption and emission measurements suggest that the dicyanovinyl unit in compound 5 is a better acceptor than formyl in compound 4, and that pyridine in compound 7 is a better π-spacer than benzene in compound 4, in exerting ICT characteristics such as fluorosolvatochromism and Stokes shifts.

DFT molecular modeling studies of D-π-A-π-D type cyclopentadithiophene-diketopyrrolopyrrole based small molecules donor materials for organic photovoltaic cells

A novel six D-π-A-π-D type compounds containing small molecules from cyclopentadithiophene (CPDT) and diketopyrrolopyrrole building (DPP) units were designed, as donors, for improving the efficiency of bulk hetero-junction solar cells. The geometries of the title compounds were optimized using the density functional theory at the hybrid functional B3LYP in combination with the 6−311 g(d,p) basis set. Electronic structures, photo-physical, optical and intra-molecular charge transfer properties have been investigated. The contour plots of the transition density matrix have been simulated for all compounds and used to evaluate the hole-electron localization, the donor-acceptor interaction as well as the electronic excitation processes in their excited states. The new designed donors have shown a large absorption in the visible range with interesting hole transport properties, resulted from their rigid-planar structures. The open circuit voltage and the fill factor were estimated. The present computational study showed that tuning the building blocks of the organic materials dispose a potential approach for further enhance the performance of small molecules donor materials in bulk hetero-junction (BHJ) organic solar cells.

Multicolor mechanochromism of a phenothiazine derivative through molecular interaction and conformational modulations

Mechanochromic luminescent (MCL) materials have attracted great attention in the fields of sensing, memory chips, and anti-counterfeiting. However, most MCL materials only display a two-color change and it is challenging to achieve multicolor mechanochromism with a single molecule. Herein, we reported a twisted D-π-A type molecule (PZ-BZ) composed of a phenothiazine (donor), 1,4-phenylene unit (π), and benzothiazole (acceptor). PZ-BZ exhibits intramolecular charge transfer and aggregation-induced emission enhancement properties. Additionally, the multicolor mechanochromic behaviour of PZ-BZ single crystal is observed. The original crystal of PZ-BZ emits cyan fluorescence (470 nm). When crushed, it exhibits blue-shifted emission (455 nm) due to the destruction of intermolecular interactions. Further grinding induces conformation planarization, resulting in large red-shifted fluorescence (503 nm). This study provides a deep insight into the molecular mechanism of multicolor mechanochromism through molecular interaction and conformation modulations.

A donor-π-acceptor aggregation-induced emission compound serving as a portable fluorescent sensor for detection and differentiation of methanol and ethanol in the gas phase

The design strategy of aggregation-induced emission (AIE) fluorophores with donor-π-acceptor (D-π-A) conjugation structure has greatly contributed to the development of luminescent materials and devices, including volatile organic compounds (VOCs) sensors. In this work, a D-π-A fluorophore DEBAB was synthesized, showing both AIE and intramolecular charge transfer (ICT) properties as confirmed by spectroscopic data and quantum chemical calculations. Furthermore, there is notable emission-enhancement when DEBAB is exposed to small-molecule alcohols, such as methanol and ethanol. Based on this phenomenon, a portable film sensor was fabricated, capable of detecting methanol and ethanol in gas phase, with detection limit (DL) as low as 8.02 ppm. Our systematic investigation suggests that hydrogen-bonding may be formed between DEBAB and alcohols, intensifying the AIE efficacy while influencing the ICT process. This working mechanism is supported by density functional theory (DFT) calculations including electrostatic potential mapping and molecular total energy. In addition, a sensor array was fabricated on a cellulose paper strip, showing different levels of emission changing in response to alcohols. Thus the detection and differentiation of methanol and ethanol are enabled.

Electron Push-Pull Effects on Intramolecular Charge Transfer in Perylene-Based Donor-Acceptor Compounds.

A series of asymmetric donor-acceptor (D-A) perylene-based compounds, 3-(N,N-bis(4'-(R)-phenyl)amino)perylene (Peri-DPA(R)), were successfully prepared to explore their intramolecular charge transfer (ICT) properties. To induce ICT between the donor and acceptor, diphenylamine (DPA) derivatives (electron donor units) with the same functional groups (R = CN, F, H, Me, or OMe) at both para positions were linked to the C-3 position of perylene to produce five Peri-DPA derivatives. A steady-state spectroscopy study on Peri-DPA(R)s exhibited a progressively regulated ICT trend consistent with the substituent effect as it progressed from the electron-withdrawing group to the electron-donating group. In particular, a comparative study using a D-A-D (donor-acceptor-donor) system demonstrated that not only the electron push-pull substituent effect but also subunit combinations influence photophysical and electrochemical properties. The different ICT characters observed in Lippert-Mataga plots of D-A(CN) and D-A-D(CN) (CN-substituted D-A and D-A-D) led to the investigation on whether ICT emission of two systems with differences in subunit combinations is of the same type or of a different type. The femtosecond transient absorption (fs-TA) spectroscopic results provided direct evidence of ICT origin and confirmed that D-A(CN) and D-A-D(CN) exhibited the same transition mix of ICT (from donor to acceptor) and reverse ICT (rICT, from arylamine to CN unit). Density functional theory (DFT)/TD-DFT calculations support the presence of ICT for all five compounds, and the experimental observations of rICT presented only for CN-substituted compounds.

Theoretical design and characterization of D-A1-A based organic dyes for efficient DSSC by altering promising acceptor (A1) moiety

The electronic, optical and photovoltaic properties of dyes can be readily tuned by modifying the structure. Herein, the thieno[2,3-b]indole (Thi)-based molecules derived from dye NTU-2 (D-A1-A) have been designed by substituting BT by DPP(O), DPP(S), QuT and BBT units and dicyanovinylene by cyanoacetic acid. Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, the regulation effect of acceptor groups on designed compounds was theoretically investigated. Indeed, in this context, the effects of various acceptor groups (A1) in D-A1-A dyes before and after binding to (TiO2)8 cluster on the electron injection have been studied. The optimized structures, electronic parameters, FMOs, NBO, PDOS analysis, the absorption spectra, and ICT parameters were evaluated to predict the suitable candidates for DSSC device. Our investigations reveal that all designed compounds have not only a significant λmax in the range of 593−824 nm, with a bandgap in the order, 2.31−1.56 eV, larger adsorption energies (Eads) and lower Λtotal, but also large light harvesting efficiency (LHE) and significant intramolecular charge transfer (ICT) properties compared to dye R. Accordingly, these theoretical calculations can provide an efficient strategy to design new promising sensitizers for DSSCs.

Fluorescent Chromophores Containing the Nitro Group: Relatively Unexplored Emissive Properties.

Apart from numerous applications, for example in azo dye precursors, explosives, and industrial processes, the nitro group (-NO2 ) appears on countless molecules in photochemical research owing to its unique characteristics such as a strong electron-withdrawing ability and facile conversion to the reduced substituent. Although it is well known as a fluorescence quencher, fluorescent chromophores that contain the nitro group have also emerged, with 3-nitrophenothiazine being recently reported to have 100 % emission quantum yield in nonpolar solvents. The diverse characters of nitro-containing chromophores motivated us to systematically review those chromophores with nitro substituents, their associated photophysical properties, and applications. In this Review, we succinctly elaborate the advance of the fluorescent nitro chromophores in fields of intramolecular charge transfer, fluorescent probes and nonlinear properties. Special attention is paid to the rationalization of the associated emission spectroscopy, so that the readers can gain insights into the structure-photophysics relationship and hence gain insights for the strategic design of nitro chromophores.

Nonlinear optical responses and ultrafast dynamics of three soluble ladder-conjugated molecules: A study on the terminal group effect

To study the structure-property relationship as well as the intramolecular charge transfer properties of typical ladder-conjugated molecules, three ladder-conjugated molecules named LT2, LT3 and BPTF-2 were systematically investigated by UV–vis absorption spectra and fluorescence spectra, the open-aperture Z-scan technique, two-photon excited fluorescence and femtosecond pump-probe experiments. These ladder-conjugated molecules employ the same fluorene group as the π-bridge and the central core, with substituent changes at the terminal position. These molecules exhibit a large two-photon absorption response and two molecules emit intense two-photon fluorescence at a wavelength of 800 nm, which is a commonly used wavelength in two-photon absorption/two-photon fluorescence applications. Our results indicate that the π-bridge and the terminal group play an important role in determining the two-photon absorption response. The dynamic results obtained from degenerated pump-probe experiments revealed that the evolution times of the intramolecular charge transfer state were >1000 ps, >1000 ps, and 40 ps for LT2, LT3 and BDTF-2, respectively. The results match those of the two-photon absorption responses and the fluorescence emission properties of these ladder-conjugated molecules. Our results also indicate that ladder-conjugated molecules have potential applications in two-photon absorption/two-photon fluorescence fields.

Synthesis, characterization, photo physical and DFT studies of bicoumarin and 3-(3-benzofuranyl)coumarin derivatives

• A series of novel bicoumarin and 3-(3-benzofuranyl)coumarin derivatives are synthesized. • Optical band gaps of the synthesized compounds were found to be 2.80–3.87 eV. • The 5% weight loss of derivatives is in the range of 239–367 °C. • The synthesized compounds are thermally stable. A series of novel bicoumarin and 3-(3-benzofuranyl) coumarin derivatives were synthesized by the reaction of salicylaldehyde and substituted coumarin 4-acetic acid/benzofuran-3-acetic acid using cyanuric chloride. The scaffolds were characterized by spectral analysis. The significant photophysical fundamentals for organic electronic applications such as thermal stability, strong and broad optical absorption were investigated for the synthesized compounds. Optical properties are studied in detail by UV-Vis absorption and fluorescence spectroscopy. Optical band gaps of the bicoumarin and 3-(3-benzofuranyl)coumarin derivatives were found to be 2.80–3.87 eV as calculated from their onset absorption edge. The bicoumarin and 3-(3-benzofuranyl)coumarin derivatives exhibit high thermal stability up to 239–367 °C. Density functional theory computation was performed to understand intramolecular charge transfer property. Photophysical studies designate that, the synthesized materials are potential candidates and play an important role in organic electronic applications.

NIR Absorbing AzaBODIPY Dyes for pH Sensing.

Two near-infrared (NIR) absorbing di(thien-2-nyl)-di(dimethylanilino)azaBODIPY dyes 2a and 2b were synthesized and characterized that differ depending on whether the dimethylaniline substituents are introduced at the 3,5- or 1,7-positions of the azaBODIPY core. The main spectral bands lie at 824 and 790 nm, respectively, in CH2Cl2. The effect of substituent position on the photophysical and pH sensing properties was analyzed through a comparison of the optical properties with the results of time-dependent density functional theory (TD-DFT) calculations. Protonation of the dimethylamino nitrogen atoms eliminates the intramolecular charge transfer properties of these compounds, and this results in a marked blue-shift of the main absorption bands to 696 and 730 nm, respectively, in CH2Cl2, and a fluorescence “turn-on” effect in the NIR region. The pH dependence studies reveal that the pKa values of the non-protonated 2a and 2b molecules are ca. 6.9 (±0.05) and 7.3 (±0.05), respectively, while that of the monoprotonated species for both dyes is ca. 1.4 (±0.05) making them potentially suitable for use as colorimetric pH indicators under highly acidic conditions.

Fluorescent Charge-Transfer Excited States in Acceptor Derivatized Thiophene Oligomers.

A family of thiophene oligomers with lengths of 3, 4, 5, 6, and 8 units were synthesized and end-capped with a strongly coupled naphthalimide acceptor (TnNIF) which produces an emissive intramolecular charge-transfer state. A thorough photophysical study was performed on the oligomers including UV-vis absorption, fluorescence, and picosecond transient absorption spectroscopy to investigate the effect of thiophene oligomer length/donor strength and solvent polarity on the intramolecular charge-transfer properties. In hexane, the TnNIF compounds behave in a manner similar to that of oligothiophenes as fluorescence from a local singlet excited state and intersystem crossing to the triplet state dominates the excited-state dynamics. Interestingly, the excited-state dynamics become much more complicated with increasing solvent polarity, from ether to acetone, where emission from a charge-transfer state (δ+TnNIF-δ) and quenching from a charge-separated state (•+TnNIF-•) become competitive. A mechanism is proposed that consists of a four-state diagram including a locally excited singlet state (1TnNIF), a triplet state (3TnNIF), an emissive charge-transfer state, and a nonemissive charge-separated state. The population of each of these states is highly dependent on both the thiophene oligomer length and solvent polarity which results in a mixture of excited states.

Unravelling photo-induced excited state dynamical process and ESIPT mechanism for 5-(diethylamino)-2-(((6-methoxybenzo[d]thiazol-2-yl)imino)methyl)phenol probe

By applying DFT and TDDFT methods, we probe into excited state luminescent properties as well as intramolecular proton transfer (ESIPT) process for a novel 5-(diethylamino)-2-(((6-methoxybenzo[d]thiazol-2-yl)imino)methyl)phenol (DMBYMP) system. We affirm intramolecular hydrogen bond of DMBYMP is supposed to become enhanced in S1. Exploring vertical excitation and charge redistribution, intramolecular charge transfer property has been found that triggers ESIPT reaction. We further construct potential energy curves and present the ultrafast ESIPT mechanism for DMBYMP. We sincerely wish this work could play roles in further developing novel applications based on DMBYMP compound and in promoting new ratiometric fluorescence probes in future.

A computational investigation of the influence of acceptor moieties on photovoltaic performances and adsorption onto the TiO2 surface in triphenylamine-based dyes for DSSC application

Five metal-free organic dyes (A1 to A5) comprising triphenylamine and vinyl-thiophene as a common donor and spacer, respectively were considered in this work. The different acceptors, such as 2-cyanoacetic acid, 2-methylenemalononitrile, rhodanine-3-acetic acid, benzoic acid, and pyridine were chosen to investigate their accepting ability, photovoltaic performances, and adsorption onto the TiO2 surface. Density functional theory (DFT) and time-dependent DFT were employed to study their photophysical and photoelectrochemical properties. The ground state energies were calculated to evaluate the dye regeneration driving force (EI3-/I--EHOMO). The excited-state calculation provided the information about the intramolecular charge transfer (ICT) and excited-state properties. Projected density of state and natural bond orbital (NBO) analyses were carried out to further understand the ICT between triphenylamine donor and the acceptor moiety. The density of states of the dye@TiO2 revealed the smooth electron transfer at the dye/TiO2 interface devoid of defect state. Higher (EI3-/I--EHOMO), highest negative NBO charge on the acceptor, lower reorganization energy, and higher negative adsorption energy onto the surface of the TiO2 would make the dye A1 as the best performer in DSSC. The computed data are in good agreement with the experimental observation.

New donor-acceptor-donor type of organic semiconductors based on the regioisomers of diketopyrrolopyrroles: A DFT study

The present work describes computational studies on structural, electronic, charge transport and photovoltaic properties of donor-acceptor-donor (D-A-D) type of compounds based on two regioisomers of diketopyrrolopyrrole. Diketopyrrolo[3,4-c]pyrrole (DPP1), a well known electron acceptor moiety and its regioisomer diketopyrrolo[3,2-b]pyrrole (DPP2) are coupled with various electron donor groups containing fused ring system to obtain model compounds of D-A-D type of architecture. The donor groups include meta-benzodithiophene, ortho-benzodithiophene, carbazole, dithienopyrrole, dithienosilole and dithienothiophene. An analysis of their properties reveal that these compounds possess unique characteristics and advantages over each other. Density functional theory (DFT) calculations show that the DPP2-based compounds exhibit lower hole reorganization energy (λh) than the corresponding DPP1-based compounds, while the DPP1-based compounds have lower electron reorganization energy (λe) than the corresponding DPP2-based compounds, which is in line with the observed ionizational potential (IP) and electron affinity (EA) values. The calculated open circuit voltage (Voc) and the fill factor (FF) values of the DPP2-based compounds as donors with fullerene-like PC61BM as an acceptor are higher than the DPP1-based compounds as donors. Charge density difference (CDD) calculation shows DPP2 based compounds exhibit better intramolecular charge transfer (ICT) properties as compared to their DPP1 counterpart. The weaker electron-hole coherence may lead to easy exciton dissociation in case of DPP1-based compounds at donor/acceptor interface, which is also supported by their comparatively lower exciton binding energy as compared to DPP2 counterparts.