Local Excitation Research Articles

Effect of A-DNA and B-DNA Conformation on the Interplay between Local Excitations and Charge-Transfer States in the Ultrafast Decay of Guanine-Cytosine Stacked Dimers: A Quantum Dynamical Investigation.

We here simulate in the gas phase the population dynamics of guanine/cytosine (GC) and cytosine/guanine (CG) stacked dimers in B-DNA and A-DNA arrangement, following excitation in the lowest-energy band, and considering the four lowest-energy ππ* bright excited states, the three lowest-energy nπ* states, and the G → C charge-transfer (CT) state. We resort to a generalized Linear Vibronic Coupling (LVC) model parametrized with time-dependent density functional theory (TD-DFT) computations, exploiting a fragment-based diabatization and we run nonadiabatic quantum dynamical simulations with the multilayer version of the Multiconfigurational Time-Dependent Hartree (ML-MCTDH) approach. G → C CT results in a major decay process for GC in B-DNA but less in A-DNA arrangement, where also the population transfer to the lowest-energy excited state localized on C is an important intermonomer process. In CG arrangements, mostly intramonomeric decays take place. We simulate the dynamics of several other GC structures whose arrangement is intermediate between B-DNA and A-DNA, obtaining further insights on the effect that the sequence and, especially, the stacking geometry have on the population transfer to the G → C CT.

Determine the Relative Aromaticity of Bilayer Graphyne, Bilayer Graphdiyne, and Bilayer Graphtriyne.

The electronic structure characteristics of bilayer graphyne, bilayer graphdiyne, and bilayer graphtriyne were systematically studied using molecular orbital (MO) analysis, density of states (DOS), and interaction region indicator (IRI) methods. The delocalization characteristics of the out-of-plane and in-plane π electrons (i.e., πout and πin electrons) of these materials were analyzed using the localized orbital locator (LOL). In addition, their responses to external magnetic fields were investigated through anisotropic induced current density (AICD) and isoscalar chemical shielding surfaces (ICSSs) to compare the induced ring currents and magnetic shielding effects, further exploring the aromaticity of the three bilayer materials. The research results indicate that as the number of alkyne groups increases, the aromaticity of the bilayer graphyne structure gradually weakens. Finally, their photophysical properties were studied through TD-DFT calculations. The results show that they exhibit strong localized excitation characteristics.

Deciphering the Photophysical Properties of Nonplanar Heterocyclic Compounds in Different Polarity Environments.

Nonplanar (butterfly-shaped) phenothiazine (PTZ) and its derivative's (M-PTZ) photophysical and spectral properties have been tuned by varying the solvents and their polarity and investigated employing spectroscopic techniques such as UV-Vis, steady-state and time-resolved fluorescence, and TDDFT calculations. The UV-Vis absorption studies and TDDFT calculations reveal two distinct bands for both compounds: a strong π-π* transition at shorter wavelengths and a weaker n-π* transition, which displays a little bathochromic shift in polar solvents. The detailed emission studies reveal that such dual emission is a result of the photoinduced excited-state conjugation enhancement (ESCE) process. The band at a shorter wavelength corresponds to the locally excited (LE) state, while the longer wavelength band arises from the planarized excited state resulting from ESCE. With the increase in solvent polarity, the LE band is less affected, whereas strong positive solvatochromism is observed for the ESCE band. As the solvent polarity increases, the ESCE band demonstrates significant positive solvatochromism, while emission intensity decreases with higher solvent polarity, suggesting stabilization of the excited state. The biexponential decay of fluorescence lifetimes further corroborates the dual emission behavior of PTZ and M-PTZ. PTZ exhibits a higher photoluminescence quantum yield (PLQY) than that observed for M-PTZ, and the solvent viscosity influences the PLQY, indicating that nonradiative decay is activated during the planarization of the excited state, also known as excited-state conjugation enhancement. Furthermore, the (time-dependent) density functional theory (TD) DFT calculations performed to understand the geometrical parameters and the electronic transitions of these model molecules further corroborate experimental findings. These findings underscore the significant influence of solvent polarity and molecular structure on the dual emission and excited-state dynamics of PTZ and M-PTZ, which eventually hold substantial implications for advanced photophysical applications.

A Manufacturing Technique for Binary Clathrate Hydrates for Cold and Very Cold Neutron Production.

Intense sources of very cold neutrons (VCNs) would be beneficial for various neutron scattering techniques and low-energy particle physics experiments. Binary clathrate hydrates hosting deuterated tetrahydrofuran (THF-d) and dioxygen show promise as potential moderators for such sources due to a rich spectrum of localized low-energy excitations of the encaged guest molecules. In this article, we present a reliable manufacturing technique for such hydrates. Neutron diffraction data confirm their clathrate structure as type II (CS-II), determine their purity, and cage occupancy. Furthermore, we present data on the thermal expansivity of THF-d- and THF-d-O2clathrates, drawing attention to them as an interesting case study for the complex structure and dynamics of this class of material.

Mechanical manipulation of electromechanical fields in multi-tunnel piezoelectric semiconductor thin film devices by creating localized transverse mechanical field excitations

Mechanical manipulation of electromechanical fields in multi-tunnel piezoelectric semiconductor thin film devices by creating localized transverse mechanical field excitations

Multicomponent synthesis of stereogenic-at-boron fluorophores (BOSPYR) from boronic acids, salicylaldehydes, and 2-formylpyrrole hydrazones.

This work describes one-step syntheses of various stereogenic-at-boron fluorochromes (BOSPYR) via multicomponent reactions involving readily accessible boronic acids, salicylaldehydes, and 2-formylpyrrole hydrazones. The dyes absorb and emit in the visible region of the electromagnetic radiation, and are characterized by large Stokes shifts (2850-4930 cm-1) with weak fluorescence emissions (Φfl: 1.5-9.1%). Notably, the dimmed fluorescence of BOSPYRs recovers upon transition to viscous media (21-fold for 1a). The representative compound 1a exhibits clear Cotton effects with dissymmetry factors of ca. |gabs| ∼ 1.9 × 10-3 in the visible region, indicating efficient asymmetry induction to the chromophore. The X-ray molecular structure of 1a shows that the chromophore deviates from planarity by 17.2°, which may contribute significantly to the inherent chirality of the fluorophore. A computational examination of excited states by time-dependent density functional theory (TD-DFT) identifies the emission mechanism as arising from a locally-excited (LE) state.

Theoretical elucidation of the effect of the linkage and orientation of carbazole and naphthalenediimide on the TADF and RTP propensities.

Thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) are most promising processes for harvesting triplet excitons in organic light-emitting diodes. In this work, the effect of the linkage between the carbazole (Cz) donor (D) and the naphthalenediimide (NDI) acceptor (A) on the TADF and RTP propensities is elucidated using density functional theory computations employing D-A, D-A-D, D-π-A, and D-π-A-π-D structural designs. The effects of the dihedral angle between the donor and acceptor units on the energy difference between the singlet and triplet excited states (ΔEST), the spin-orbit coupling (SOC) constants, and radiative (kr), intersystem crossing (kISC) and reverse intersystem crossing (kRISC) rates are unravelled. The molecules possessing a direct linkage between Cz and NDI exhibit large ΔEST values due to substantial overlap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). However, the insertion of a phenyl spacer between the Cz and NDI units led to disjoint HOMO and LUMO and consequently resulted in a small ΔEST. Furthermore, the presence of two donors with and without a phenyl spacer on NDI resulted in a high-lying triplet state (T2) that is energetically lower than the lowest singlet excited state (S1), hence providing additional channels to the TADF and RTP processes. Also, the orientation of Cz and NDI in the ortho-positions of the phenyl unit resulted in a T1 state with dominant LE character which led to moderate spin-orbit coupling constants and highest kr rates compared to the analogous meta- and para-linked derivatives. Thus, the ortho-derivatives possessed small ΔEST, charge transfer dominated S1, joint holes and electrons for the T1 state, characteristic of local excitation, high SOC, and promising rISC and kr rates. Overall, the phenyl linked derivatives possess TADF characteristics, while the directly linked analogues show RTP propensity.

Kevlar-Covered Subresonant Pressure Sensor for Flow Measurements

This study presents wall pressure sensors based on wall-flush Kevlar-covered cavities. The sensor dynamic response is characterized using a variety of acoustic and flow experiments, including a flow disturbance quantification performed using wall-parallel particle image velocimetry. Various sensor configurations are studied to understand the relation between cavity shape and Kevlar scrim on the sensor response. Using a localized excitation study, the sensor’s spatial sensitivity is characterized, and a mathematical model to estimate the wall pressure spectrum is presented. It is shown that these sensors have a well-defined, second-order dynamic response without grazing flow. Their performance in flow shows the disturbance to the flow below the measurement uncertainty, indicating no significant flow disturbance. Comparing measured data with the model estimates reveals close agreement, within ±3 dB, and that discrepancy is accounted for by grazing flow effects and sensor spatial sensitivity.

Effect of the incorporation of gold nanoparticles on the current‒voltage characteristics of Ag/Si diodes in the dark and under light

The use of nanoparticles in electronic devices has become common practice for controlling and improving device performance. In this research, gold nanoparticles (AuNPs) were introduced into silver‒silicon (Ag/Si) Schottky diodes to investigate their impact on the current voltage (I‒V) behavior in both the dark and light surroundings. Spin coating was used to deposit a film of AuNPs on the Si substrate, followed by thermal evaporation of Ag metal to create the concluding Ag/AuNP/Si diode. Study of the I‒V curves revealed a reduction in the barrier height after the addition of AuNPs in both the dark and illuminated settings. Furthermore, the presence of AuNPs led to a decrease in both the series (Rs) and shunt (Rsh) resistances when the diode was exposed to light, indicating an improvement in the photosensitivity of the Ag/Si structures. This enhancement was attributed to the ability of AuNPs to increase light absorption through local interface plasmon excitations, resulting from the shared oscillation of free electrons on metallic surfaces

Photophysical behavior of meso-N-butylcarbazole-substituted BODIPY in different nano-scale organized media.

The present work focuses on the photophysical behavior of meso-N-butylcarbazole-substituted BODIPY (CBZ-BDP) in different organized media towards exploring the possible use of the dye as a molecular sensor and imaging agent. The molecule shows an appreciable change in absorption and emission spectra at 75% water-acetonitrile mixture compared to pure acetonitrile. In water-acetonitrile mixture, it displays aggregate-induced emission (AIE) bands. New emission peaks are observed at 560nm and 630nm, corresponding to LE (locally excited) and ICT (intramolecular charge transfer) states of CBZ-BDP aggregates. The fluorescence anisotropy studies of CBZ-BDP in glycerol medium show its better sensitivity towards the microenvironment. CBZ-BDP was used to probe various microheterogeneous systems like bile salts, pluronics, and lipid bilayer systems in aqueous medium. The dye displays sensitive variation in emission intensity and fluorescence anisotropy in sodium cholate (NaC) bile salt in aqueous medium as a function of the bile salt concentration. The molecule detects the temperature-induced phase transitions in pluronic P123 and F127, as well as 1,2-dimyristoylphosphatidylcholine (DMPC)and 1,2-dipalmitoylphosphatidylcholine (DPPC) lipid bilayer systems in aqueous medium. These studies strongly suggest that CBZ-BDP can be used as an efficient fluorescent probe in sensing the micro-environmental changes in bile salts, pluronics, and lipid bilayers in aqueous medium. The imaging studies of CBZ-BDP-embedded Giant Unilamellar Vesicles (GUVs) were carried out. The molecule stains the lipid bilayers and displays bright-green fluorescent images, suggesting its potential in lipid bilayer imaging.

Computing Excited States of Very Large Systems with Range-Separated Hybrid Functionals and the Exact Integral Simplified Time-Dependent Density Functional Theory (XsTD-DFT).

Simplified quantum chemistry (sQC) methods can routinely compute excited states for very large systems in an "all-atom" fashion. They are viable alternatives to regular multiscale schemes. sQC methods have the advantage of accounting explicitly for all of the environment at a quantum mechanical (QM) level. The treatment of charge-transfer states is now improved by the native implementation of range-separated hybrid (RSH) exchange-correlation functionals into the eXact integral simplified time-dependent density functional theory (XsTD-DFT). After the RSH XsTD-DFT/TDA scheme was benchmarked, XsTD-DFT(/TDA) ultraviolet/visible absorption, circular dichroism (CD), and/or two-photon absorption (2PA) spectra were directly compared to the results of experiments for four challenging and increasingly large systems: eYFP model system, Λ-shaped multimodular D-π-A-π-D'-π-A-π-D chromophore, mixed donor/acceptor ligand Pd(II) double cage [3BF4@Pd4DmA8-m], and the photoactive yellow protein (PYP). Among the results, this study shows that an "all-atom" approach is unavoidable for reproducing absorption and CD spectra of PYP because one of the main transitions involves a local excitation on a tryptophan.

Regioregular Poly(p‐phenylene iminoborane): A Strictly Alternating BN‐Isostere of Poly(p‐phenylene vinylene) with Stimuli‐Responsive Behavior

AbstractIncorporation of BN units into π‐conjugated organic compounds, as substitutes for specific CC couples, often leads to new hybrid materials with modified physical and chemical properties. Poly(p‐phenylene iminoborane)s are derived from well‐known poly(p‐phenylene vinylene) (PPV) by replacement of the vinylene groups by B=N linking units. Herein, an unprecedented poly(p‐phenylene iminoborane) is presented that features a strictly alternating sequence of BN units along the main chain. The synthesis thereof was achieved by AB‐type polymerization of a monomer featuring an N and a B terminus. Monodisperse oligomers with up to three BN units in the chain were additionally prepared and structurally characterized. Associated with the introduction of a dipole in the regioregular backbone structure, they display notable fluorescence already in solution and large Stokes shifts, distinct from their previously reported BBNN‐sequenced congeners. All compounds show aggregation‐induced emission enhancement (AIEE) properties. Computational studies provided evidence for emission from either locally excited (LE) or twisted intramolecular charge transfer (TICT) states. These processes can be optionally addressed by various stimuli, giving rise to dual emission, solvatochromic, thermochromic, and reversible mechanochromic behavior.

Regioregular Poly(p-phenylene iminoborane): A Strictly Alternating BN-Isostere of Poly(p-phenylene vinylene) with Stimuli-Responsive Behavior.

Incorporation of BN units into π-conjugated organic compounds, as substitutes for specific CC couples, often leads to new hybrid materials with modified physical and chemical properties. Poly(p-phenylene iminoborane)s are derived from well-known poly(p-phenylene vinylene) (PPV) by replacement of the vinylene groups by B=N linking units. Herein, an unprecedented poly(p-phenylene iminoborane) is presented that features a strictly alternating sequence of BN units along the main chain. The synthesis thereof was achieved by AB-type polymerization of a monomer featuring an N and a B terminus. Monodisperse oligomers with up to three BN units in the chain were additionally prepared and structurally characterized. Associated with the introduction of a dipole in the regioregular backbone structure, they display notable fluorescence already in solution and large Stokes shifts, distinct from their previously reported BBNN-sequenced congeners. All compounds show aggregation-induced emission enhancement (AIEE) properties. Computational studies provided evidence for emission from either locally excited (LE) or twisted intramolecular charge transfer (TICT) states. These processes can be optionally addressed by various stimuli, giving rise to dual emission, solvatochromic, thermochromic, and reversible mechanochromic behavior.

(Invited) Emissive Charge-Transfer Excited-State between Organic Conjugated Molecule and Two-Dimensional Inorganic Nanosheet

The unique properties of two-dimensional (2D) materials have boosted intensive interests in combining distinct 2D materials into organic-inorganic heteronanostructure interfaces for device and sensor applications. The hetero-interfaces, integrating atomically thin inorganic materials with an unlimited variety of organic molecules, provide an ideal platform for broader, superior, and on-demand functional applications by incorporating customized organic molecules that particularly exhibit excellent optical and optoelectronic properties. Especially, unique electronic and optical properties discovered for mono- or few-layered transition metal dichalcogenides, represented by MoS2, have rendered them as suitable platforms to host organic π-conjugated compounds. As such, there have been investigations on photodynamic processes at interfaces between MoS2 and various π-conjugated compounds.1 However, previously reported hybrid interfaces were constructed by amorphous-deposition or covalent linkage using long, flexible bridges and thus, the inhomogeneous interfacial structures make it difficult to elucidate the relationship between the interface structure and photodynamics.In this study, we designed and synthesized a hetero-nanostructure interface between an organic π-conjugated molecule (pyrene, Py) and 2D inorganic nanosheet (mono- or few-layered MoS2) with a well-defined bridge at a molecular level (Figure 1).2 As the bridge between Py and MoS2 basal plane, we employed N-benzylsuccineimide structure to form Py-Bn-MoS2.Spectroscopic measurements revealed that the locally-excited (LE) state of pyrene in Py-Bn-MoS2 efficiently generates a long-lived charge-transfer (CT) excited state that straddles the interface of pyrene–MoS2 nanosheet. The CT excited-state is highly emissive (0.68) and relaxes to the ground state without forming the complete charge-separated (CS) state. To the best of our knowledge, this is the first observation of unusually intense emission from the CT excited state at well-defined hetero-nanostructure interface of organic π-conjugated molecules and 2D inorganic nanosheets. Theoretical studies elucidated the interaction of MoS2 vacant orbitals with the pyrene LE state to form the CT excited-state showing distinct solvent dependence of the emission energy. These findings provide important implications for manipulating the LE, CT, and CS states at the interface of photoactive organic molecules and inorganic semiconducting nanosheets. References Baek, J.; Umeyama, T.; Choi, W.; Tsutsui, Y.; Yamada, H.; Seki, S.; Imahori, H. Formation and Photodynamic Behavior of Transition Metal Dichalcogenide Nanosheet-Fullerene Inorganic/Organic Nanohybrids on Semiconducting Electrodes. Chem. Eur. J. 2018, 24, 1561−1572.Umeyama, T.; Mizutani, D.; Ikeda, Y.; Osterloh, W. R.; Yamamoto, F.; Kato, K.; Yamakata, A.; Higashi, M.; Urakami, T.; Sato, H.; Imahori, H. Emissive Charge-Transfer Excited-State at Well-Defined Hetero-Nanostructure Interface of Organic Conjugated Molecule and Two-Dimensional Inorganic Nanosheet. Chem. Sci. 2023, 14, 11914−11923. Figure 1

Quantum Magnetic Skyrmion Operator.

We propose a variational wave function to represent quantum skyrmions as bosonic operators. The operator faithfully reproduces two fundamental features of quantum skyrmions: their classical magnetic order and a "quantum cloud" of local spin-flip excitations. Using exact numerical simulations of the ground states of a 2D chiral magnetic model, we find two regions in the single-skyrmion state diagram distinguished by their leading quantum corrections. We use matrix product state simulations of the adiabatic braiding of two skyrmions to verify that the operator representation of skyrmions is valid at large interskyrmion distances. Our work demonstrates that skyrmions can be approximately coarse-grained and represented by bosonic quasiparticles, which paves the way toward a field theory of many-skyrmion quantum phases and, unlike other approaches, incorporates the microscopic quantum fluctuations of individual skyrmions.

Trion sensing of a zero-field composite Fermi liquid.

The half-filled lowest Landau level is a fascinating platform for researching interacting topological phases. A celebrated example is the composite Fermi liquid, a non-Fermi liquid formed by composite fermions in strong magnetic fields1-10. Its zero-field counterpart is predicted in atwisted MoTe2 bilayer (tMoTe2)11,12-a recently discovered fractional Chern insulator exhibiting the fractional quantum anomalous Hall effect13-16. Although transport measurements at ν = -1/2 show signatures consistent with a zero-field composite Fermi liquid14, new probes are crucial to investigate the state and its elementary excitations. Here, by using the unique valley properties of tMoTe2, we report optical signatures of a zero-field composite Fermi liquid. We measured the degree of circular polarization (ρ) of trion photoluminescence versus hole doping and electric field. We found that, within the phase space showing robust ferromagnetism, ρ is near unity for Fermi liquid states. However, ρ is quenched at both integer andfractional Chern insulators, and in a holedoping range near ν = -1/2. Temperature, optical excitation power and electric-field-dependence measurements demonstrate that the quenching of ρ is a direct consequence of an energy gap (pseudogap) for electronic excitations of the Chern insulators (composite Fermi liquid): because the local spin-polarized excitations necessary to form trions are strongly suppressed, trion formation at the corresponding filling factors relies on optically generated unpolarized itinerant holes. Our work highlights a new excitonic probe of zero-field fractional Chern insulator physics, unique to tMoTe2.

Near-Infrared Light-Driven CO2 Reduction on Cup-Stacked Carbon Nanotubes.

Carbon nanotubes feature one-dimensional nature of collective excitations, wherein strong confinement of surface plasmons severely hinders the liberation of hot electrons (HEs), posing grand challenges for their utilization in photochemistry. In this study, we prototypically achieved directed HEs flow and extraction in hybrid plasmonic CNN based on cup-stacked carbon nanotubes (CSCNTs), taking advantage of their privileged edge-plane sites. The localized pz electronic states and accessible intersubband plasmon excitations in the near-infrared (NIR) regime stands in striking contrast to the conventional concentric carbon nanotubes, as evidenced by combined photo-induced force microscopy (PiFM) and transient photocurrent response. The hybrid comprising intimately integrated CSCNTs-C3N4 effectively sustains interfacial electronic states and underlies the energy extraction out of plasmonic components. The CNN demonstrates almost near-unity NIR light-driven CO2 reduction to CO with a rate of 1.35 μmol g-1 h-1. This work sheds light on the exploitation of metal-free carbon-based plasmonic nanostructures for photocatalytic applications.

Near‐Infrared Light‐Driven CO2 Reduction on Cup‐Stacked Carbon Nanotubes

AbstractCarbon nanotubes feature one‐dimensional nature of collective excitations, wherein strong confinement of surface plasmons severely hinders the liberation of hot electrons (HEs), posing grand challenges for their utilization in photochemistry. In this study, we prototypically achieved directed HEs flow and extraction in hybrid plasmonic CNN based on cup‐stacked carbon nanotubes (CSCNTs), taking advantage of their privileged edge‐plane sites. The localized pz electronic states and accessible intersubband plasmon excitations in the near‐infrared (NIR) regime stands in striking contrast to the conventional concentric carbon nanotubes, as evidenced by combined photo‐induced force microscopy (PiFM) and transient photocurrent response. The hybrid comprising intimately integrated CSCNTs‐C3N4 effectively sustains interfacial electronic states and underlies the energy extraction out of plasmonic components. The CNN demonstrates almost near‐unity NIR light‐driven CO2 reduction to CO with a rate of 1.35 μmol g−1 h−1. This work sheds light on the exploitation of metal‐free carbon‐based plasmonic nanostructures for photocatalytic applications.

A novel rhodopsin-based voltage indicator for simultaneous two-photon optical recording with GCaMP in vivo.

Genetically encoded voltage indicators (GEVIs) allow optical recording of membrane potential from targeted cells in vivo. However, red GEVIs that are compatible with two-photon microscopy and that can be multiplexed in vivo with green reporters like GCaMP, are currently lacking. To address this gap, we explored diverse rhodopsin proteins as GEVIs and engineered a novel GEVI, 2Photron, based on a rhodopsin from the green algae Klebsormidium nitens. 2Photron, combined with two photon ultrafast local volume excitation (ULoVE), enabled multiplexed readout of spiking and subthreshold voltage simultaneously with GCaMP calcium signals in visual cortical neurons of awake, behaving mice. These recordings revealed the cell-specific relationship of spiking and subthreshold voltage dynamics with GCaMP responses, highlighting the challenges of extracting underlying spike trains from calcium imaging.

Investigating Excited States and Absorption Spectra of the Poly-cyclopenta-dithiophene-benzothiadiazole Oligomers (Poly-CPDTBT)-A Theoretical Study.

Poly-CPDTBT, as typical low-band gap copolymers, have potential applications in organic bulk heterojunction solar cells. To have a clear picture of its excited-state processes, the first task is to understand their excited states, in particular, electronic character and relevant optical absorption. Herein, the low-lying singlet excited states of Poly-CPDTBT oligomers were investigated via Algebraic Diagrammatic Construction Second Order (ADC(2)) and time-dependent density functional theory (TDDFT) method with several functionals. Six CPDTBTN (N = 1-6) oligomers were taken as prototypes to study their excited states in detail. The results provide interesting clues to extrapolate the photophysical properties of such polymers with potential applications in photovoltaic materials. The result provided by ωB97XD functional gives good agreement with the experiment result. The vertical excitation energies of the four lowest excited states decrease almost linearly with increasing polymerization degree (N) for CPDTBTN (N = 1-6). The transition density analysis indicates that the local excitations (LE) and the short-distance charge transfer (CT) excitations between two adjacent CPDT and BT units are dominant for low-lying excited states for short oligomers. For the long-chain oligomers (trimer to hexamer), the transition density shows a ladder (or zigzag) pattern along the diagonal blocks at the planar geometry. For long oligomers, the whole chain is involved in the transitions, and the CT excitations only exist between two adjacent CPDT and BT units. The present work provides a valuable basis for understanding the excited-state processes of Poly-CPDTBT and other conjugated polymers that conduct solar energy conversions, which has great significance for the development of new solar cells.