Influence of azacycle donor moieties on the photovoltaic properties of benzo[c][1,2,5]thiadiazole based organic systems: a dft study

ABSTRACT Fullerene free organic chromophores are widely utilized to improve the efficacy of photovoltaic materials. Herein, we designed D-π-A-π-D form chromophores (TAZD1-TAZD5) via

end-capped redistribution of donor moieties by keeping the same π-bridge and central acceptor unit for organic solar cells (OSCs). To analyze the photovoltaic characteristics of these

derivatives, DFT estimations were accomplished at B3LYP/6–311 G (d,p) functional. Different investigations like frontier molecular orbital (FMO), absorption spectra (UV–Vis), density of

states (DOS), binding energy (Eb), open circuit voltage (_V__oc_), and transition density matrix (TDMs) were performed to examine the optical, photophysical and electronic characteristics of

afore-mentioned chromophores. A suitable band gap (∆E = 2.723–2.659 eV) with larger bathochromic shift (_λ_max = 554.218–543.261 nm in acetonitrile) was seen in TAZD1-TAZD5. An effective

charge transference from donor to acceptor via spacer was observed by FMO analysis which further supported by DOS and TDM. Further, lower binding energy values also supported the higher

exciton dissociation and greater CT in TAZD1-TAZD5. Among all the designed chromophores, TAZD5 exhibited the narrowest _E_gap (2.659 eV) and maximum red-shifted absorption in solvent as well

as gas phase i.e. 554.218 nm and 533.219 nm, respectively which perhaps as a result of the phenothiazine-based donor group (MPT). In a nutshell, all the tailored chromophores can be

considered as efficient compounds for promising OSCs with a good _V_oc response, interestingly, TAZD5 is found to be excellent chromophores as compared to all these designed compounds.

SIMILAR CONTENT BEING VIEWED BY OTHERS EXPLORATION OF THE EFFECT OF MULTIPLE ACCEPTOR AND Π–SPACER MOIETIES COUPLED TO INDOLONAPHTHYRIDINE CORE FOR PROMISING ORGANIC PHOTOVOLTAIC  

PROPERTIES: A FIRST PRINCIPLES FRAMEWORK Article Open access 27 August 2024 FIRST THEORETICAL FRAMEWORK FOR HIGHLY EFFICIENT PHOTOVOLTAIC PARAMETERS BY STRUCTURAL MODIFICATION WITH

BENZOTHIOPHENE-INCORPORATED ACCEPTORS IN DITHIOPHENE BASED CHROMOPHORES Article Open access 23 November 2022 EXPLORATION OF SELENOPHENE ANALOGUE AND DIFFERENT ACCEPTOR INFLUENCE ON

PHOTOVOLTAIC PROPERTIES OF PYRROLE-4,6(5-_H_)-DIONE BASED CHROMOPHORES VIA QUANTUM CHEMICAL INVESTIGATIONS Article Open access 28 April 2025 INTRODUCTION Solar energy has turn into a

promising energy source which involve the phenomena of photoelectric effect and overcome the elevating power crisis as the sunlight is non-exhaustible, non-polluting and widely available1.

Among promising and cost-effective substitutes for future sustainable energy are OSCs due to their exceptional advantages. OSCs have been proved as an effective scheme for light

manipulation, which is capable of improving the light absorption process2. In this way, larger photocurrent is produced due to the light scattering. The photovoltaic innovation has gained

consideration of academic along with industrial communities’ decades-long. The photovoltaic (PV) silicon-based solar cells were known as the foremost and popular energy gadgets owing to

their remarkable eco-friendly nature, proficiency and low cost3. Crystalline silicon solar cells have the greatest manufacturing history with over 60 years of progress and their efficiency

has increased to above 25% because of the improvements in their architecture4,5. However, they are fragile and possess non-tunable energy levels due to which the organic-based solar cells

have become more popular in recent years. They possess various important characteristics such as; (i) light weight; (ii) low-cost materials; (iii) tunable energy levels; (iv) mechanical

flexibility; (v) variety of structural modulations and (vi) compatibility with large manufacturing6,7,8,9. Furthermore, organic–inorganic perovskite photovoltaics have gained impressive

power conversion efficiency (PCE) of 22.1% because of remarkable characteristics like intense absorption spectrum, greater charge mobility and long diffusion length of charges10,11,12.

Another class of OSCs namely dye-sensitized solar cells (DSSC) has also captured significant attention owing to their stability besides tunable visual characteristics e.g. transparency and

color13,14,15. Components in DSSCs, such as the dye catches special attention on because of light conversion capability to electricity supported by photoexcitation13. The DSSCs that are

metal free are of great efficiency and advantageous because of their synthesis, purification and many optical properties by easy chemical modifications16. Although in beginning efforts to

commercialize organic photovoltaics (OPVs) were difficult as a result of lower power conversion efficiency (PCE) than the approximated market viability of 15%17. Besides, the photovoltaic

domain is developed with other very compelling substances like OSCs based on fullerene derivatives namely PC71BM, ICBA, and PC61BM. Organic solar cells (OSCs) keeping fascinating

characteristics like simple processability, light weight, mechanical flexibility, high formulation area and ease made them significant alternative tools18,19,20,21. Due to the exceptional

electronic and structural properties of fullerene-based OSCs, they have been widely examined since 198522. Low reorganization energy of excitons23,24, elevated electron affinity25, and high

mobility of electrons26,27 are some fascinating and distinctive properties of fullerene based OSCs. There also exhibit certain drawbacks in fullerene acceptors (FAs) which include less

absorption in visible and near IR regions, poor photochemical and thermal stability28, non-tunable LUMO energies29 and less sunshine assimilation which impelled the researchers to search for

some more strongly absorbing analogues30. Therefore, non-fullerene acceptors (NFAs) are utilized in the OSCs in place of FA owing to their flexible nature, higher fabrication area and wide

tunability of their energy levels31. The non-fullerene small molecule acceptors (NF-SMAs) are regarded as remarkable constituents for proficient OSCs32. A rapid improvement in PCE is

observed (~ 18–19%) in NFAs benefiting from years of research on fullerene-based BHJ materials33,34. The obvious increase in fill factor (FF) as well as short-circuit current (_J_sc) is also

seen in NFA-based devices with greater open-circuit voltage (_V_oc) in comparison to their fullerene counterparts35. Literature is flooded with many examples in which fullerene free donor

or acceptors are extensively utilized to improve the efficiencies of photovoltaic materials36,37,38,39. Keeping in view the importance of NF organic systems, herein, we have tried to design

benzodithiophene based organic systems for high efficacy photovoltaic devices. For this purpose, we take a synthesized X94FIC40 fullerene free A-π-A-π-A architecture acceptor nature molecule

and designed sequence of donor type D-π-A-π-D configured TAZD1-TAZD5 chromophores by structural modification of end capped acceptors with efficient donor moieties. Perhaps, it is first ever

systematic comparative study of impact of NF chromophores with five-, six- and seven-membered rings on the electrochemical as well as photophysical characteristics. To check the influence

of donor groups on photovoltaic characteristics, DFT method was employed and has anticipated their significance in OSCs. COMPUTATIONAL PROCEDURE Gaussian 09 package41 was exploited to

understand the photovoltaic response of benzodithiophene based organic (TAZD1-TAZD5). To choose the suitable functional for current investigation, a relative investigation of X94FIC _λ_max

outcomes among several TD-DFT functionals and experimental results was performed. For this purpose, the reference chromophore X94FIC was subjected to geometry optimization using four

different functionals, including B3LYP42, M0643, MPW1PW9144 and ɷB97XD45 in acetonitrile solvent as range-separated functionals estimates HOMO–LUMO gaps and excited-state energies

better46,47,48,49. Then these optimized geometries were applied to execute UV–Vis analysis in acetonitrile solvent and 818.864, 736.686, 676.142, and 495.461 nm values of _λ_max were

obtained at aforesaid functionals, respectively. The _λ_max values of X94FIC obtained using these functionals were compared to the experimentally determined maximum absorption value of 783 

_nm_39 of X94FIC chromophore. At B3LYP/6-311G (d,p) functional, closed harmony was seen with experimental results. Moreover, we also compared the band gap values of X94FIC calculated at

aforesaid functional of TD-DFT (1.774, 2.142, 2.032 and 4.971 eV_,_ respectively) with experimental ΔE value (1.41 eV)39 and interesting, good harmony with experimental results was seen at

B3LYP, hence, this functional was selected for this study. First of all, structures of designed systems were optimized at B3LYP/6-311G(d,p) to get true minima geometries in acetonitrile

solvent. The absence of any imaginary frequency specified that structures were at true minima potential energy surface. After the successful optimization of geometries, different analyses;

FMOs, DOS, UV–Vis, _V_oc, Eb and TDMs were attained to inspect the optical, electronic and photophysical characteristics of afore-mentioned chromophores at B3LYP/6-311G (d,p) level of

DFT/TDDFT in acetonitrile solvent. Nevertheless, in order to understand the effect of different media on UV–Vis properties, we performed absorption analysis in gas and acetonitrile at

foresaid functional. For the extraction of data from output files, Gauss View 5.0 program50, Avogadro51, Chemcraft52, PyMOlyze 2.053, and Origin54 software were utilized and the data was

recorded in the form of graphs and tables. RESULTS AND DISCUSSION In current era, fullerene free-organic systems (FF-OSs) with some special architectures like D-π-A-π-D, A-π-A-π-A55, A-D-A56

and A-π-A gain significant importance in improving the efficiency of solar cell materials57,58,59. Therefore, in current study we formulated a range of donor nature chromophores

(TAZD1-TAZD5) with D-π-A-π-D framework from a synthesized system X94FIC (A-π-A-π-A)40 by molecular replacement at the terminals with efficient azacycle donor moieties (see Fig. 2). First of

all, we designed TAZD1 from X94FIC by replacing its terminal acceptors with four rings azacycle donor unit (9-phenyl-9H-carbazole) keeping the central ‘π-linker’ and ‘A’ same as shown in

Fig. 1. After that TAZD2-TAZD5 are designed by replacing the four member azacycle donor rings unit with three, five and six member ring azacycle donor unit as exhibited in Fig. 2. The

optimized structures of aforesaid systems are displayed in Fig. 3 while their Chemdraw structures are shown in Fig. S2, however, their IUPAC names are tabulated in Table S1. The utilized

azacycle donor moieties: 9-phenyl-9H-carbazole (THC), 5-phenyl-10,11-dihydro-5H-dibenzo[b,f]azepine (THA), 5-phenyl-5H-dibenzo[b,f]azepine (TBA), 9,9,10-triphenyl-9,10-dihydroacridine (PTH),

3-methyl-10H-phenothiazine (MPT) and their structures can be seen in Fig. S1. We have calculated different parameters like FMOs, DOS, UV–Vis, _V__oc_, Eb and TDMs of all the studied

compounds. The modifications in derivatives with their respective donor moieties might prove as a significant step towards introducing efficient solar cells. FRONTIER MOLECULAR ORBITALS

(FMOS) ANALYSIS The optoelectronic properties i.e. charge transfer, electronic features, reactivity, chemical stability and molecular interactions60 are investigated via utilizing

FMOs61,62,63. The band gap of HOMO/LUMO orbitals is closely linked to these parameters64. As HOMO is the electronically filled highest orbital, so it is considered as an electron

contributor, whereas, LUMO is considered to be an electron acceptor as it is an empty or unfilled orbital. Molecules having high energy gap (_E_gap) values are hard, because they resist

changes in electronic configurations, resulting in lower reactivity and increased kinetic stability. Conversely, the compounds with low energy gap are attributed as soft molecules owing to

their less stability and higher reactivity. These compounds reveal strong intramolecular charge transfer (ICT) possibilities due to their highly polarized nature and are extremely efficient

molecules in the production of solar cell materials65. In addition, the HOMO–LUMO band difference is important in calculating a molecule’s total _V__oc_ and _E_b64. So, FMO analysis is used

to compute _E_HOMO, _E_LUMO and _E_gap of TAZD1-TAZD5 and the outcomes are exhibited in Table 1. The pictographs showing charge transference among orbitals are depicted in Fig. 4. The above

table reveals HOMO energy values for TAZD1, TAZD2, TAZD3, TAZD4 and TAZD5 as − 5.177, − 5.185, − 5.185, − 5.199 and − 5.104 eV while energies of LUMO are − 2.469, − 2.467, − 2.463, − 2.476

and − 2.445 eV_,_ correspondingly. _E_gap is used to calculate molecules conductivity and net charge transfer66,67. The _E_gap values of designed chromophores (TAZD1-TAZD5) are revealed as

2.708, 2.718, 2.722, 2.723 and 2.659 eV, correspondingly. Highest energy difference between HOMO and LUMO (2.723 eV) is observed in TAZD4 among all the other derivatives which may be due to

the 9,9-diphenyl-10-(p-tolyl)-9,10-dihydroacridine (PTH) donor moiety. The _E__gap_ value is abridged to 2.722 eV in TAZD3 due to the substitution of PTH with

5-(p-tolyl)-5H-dibenzo[b,f]azepine (TBA) donor moiety which may be due to the decreased in hindrance in charge transfer of TBA as compared to that of PTH. Furthermore, the replacement of

donor of TAZD3 i.e. TBA with 5-(p-tolyl)-10,11-dihydro-5H-dibenzo[b,f]azepine (THA) in TAZD2 resulted in further reduction of bandgap to 2.718 eV owing to the enhancement in conjugation in

the newly introduced donor moiety. TAZD1 is designed via replacing THA with carbazole containing donor moiety i.e. 9-(p-tolyl)-9H-carbazole (THC) in which nitrogen atom of carbazole exhibit

the electron donating capability. As a result of this, the energy difference is lessen to 2.708 eV in TAZD1 because of the enhanced push pull mechanism. Moreover, TAZD5 has exhibited minimum

energy gap as compared to all of the studied chromophores owing to the use of phenothiazine-based donor moiety such as 3-methyl-10H-phenothiazine (MPT) instead of THC in TAZD1. The extra

electron-rich sulphur atom in phenothiazine might give an improved electron-donating capacity compared to donors that just include nitrogen atoms, like carbazole. Overall, the band gap

descending order in the studied compounds is; TAZD4 > TAZD3 > TAZD2 > TAZD1 > TAZD5. The electron density in HOMO of TAZD1-TAZD4 is predominantly located over the center ‘A’ and

‘π-spacer’ parts of the organic systems and minor over some atoms of donor, while in TAZD5 the electron density is dispersed on entire system. For LUMO, the electron density is majorly

located over π-bridge and core acceptor in TAZD1-TAZD5. Among all the investigated compounds, TAZD5 is found to be the appropriate candidate for future OSCs with enhanced PV behavior due to

less energy band gap and adequate charges transition from terminal donors to center acceptor (see Fig. 4). UV–VIS ANALYSIS UV–Vis analysis is significant to investigate the possibility of

ICT, kind of configurations of transitions and electronic transitions in a compound. To calculate the absorption spectra of the excited states, the TD-DFT calculations are accomplished in

gas and acetonitrile solvent. The observed oscillator strength (_f_os), transition energy (_E_), transition type and maximum absorption wavelength (_λ_max) are shown in Table 2 as well as

Table 3 and other transitions are represented in Tables S2–S11, whereas the absorption spectra of studied compounds TAZD1-TAZD5 is displayed in Fig. 5. In solvent (acetonitrile), all the

investigated compounds have revealed maximum absorbance in visible spectrum (Fig. 5). The designed molecules (TAZD1-TAZD5) exhibit absorption range from 543.361 to 554.218 _nm_ in

acetonitrile. In solvent phase, _λ_max values are found to be more red-shifted contrary to gas phase because of solvent effect. Furthermore, the absorption spectra of studied compounds

(TAZD1-TAZD5) are dominated by π-π interactions68. The polar medium results in the stabilization of π-π* state associated with n-π* characteristics by the use of an efficient electronic

state69. This indicates that, in the stabilization of first singlet state, hydrogen bonding and dipole interactions are imperative70 and the molecules exhibit red-shifted absorption as a

result of enhancement of solvent polarity. It is seen that, \(\lambda\)max values are controlled efficiently by end-capped donor moieties which successively drive the red shifted absorption

spectra71,72. The absorption band of TAZD4 is noticed at 543.361 nm having 2.282 eV energy of transition, 1.031 _f_os by exhibiting 98% molecular orbital contribution from HOMO to LUMO. The

computed _λ_max value is shifted towards bathochromic shift in TAZD3 due to the replacement of PTH donor of TAZD4 by TBA so, TAZD3 has exhibited _λ_max at 544.101 nm, 2.279 eV transition

energy, and 0.964 oscillator strength via showing HOMO → LUMO MO contribution of 98%. Furthermore, the substitution of TBA with THA donor moiety resulted in red-shifted absorption of 544.483

 nm in TAZD2 along with lower transition energy (2.277 eV) and 1.006 oscillator strength via same MO contributions. Additionally, TAZD1 absorption spectra further shifted towards

bathochromic shift (546.427 nm), owing to the deposition of another donor moiety _i.e.,_ THC in TAZD1 in the replacement of THA in TAZD2. Finally, the substitution of TTC with MPT donor

moiety resulted in maximum red shift of 554.218 nm in TAZD5 due to phenothiazine group in MPT by showing 96% HOMO → LUMO and 2% HOMO-2 → LUMO molecular orbital contribution at 1.005

oscillator strength and minimum transition energy (2.237 eV) owing to its lowest band gap. \(\lambda\)max of all the compounds in acetonitrile solvent is found to be in increasing order as

TAZD4 < TAZD3 < TAZD2 < TAZD1 < TAZD5. In gaseous phase (Table 3), all the entitled compounds have almost exhibited equivalent order as well as characteristics as in solvent

phase. The absorption spectrum shifts towards the red shift as the dielectric constant of media enhanced. Therefore, greater bathochromic shift is seen in acetonitrile due to its higher

dielectric constant than that of gas phase. Nevertheless, it can be concluded from above discussion that, TAZD5 compound has exhibited maximum absorption wavelength, the lowest transition

energy and minimum band gap which implies that, it can be used as an efficient material for photophysical characteristics in non-fullerene OSC materials. OPEN CIRCUIT VOLTAGE Open circuit

voltage (_V_oc) is another significant study that provides insights into the performance of OSCs i.e. their maximum working capability. The total current that can be produced via any optical

system can be estimated by _V__oc_31,55. So, _V_oc shows direct relation with _E_HOMO and _E_LUMO of donor and acceptor molecules, correspondingly. Thus, _V_oc outcomes of TAZD1-TAZD5 are

determined via Eq. (1) proposed by Scharber and his coworkers. $$V\mathrm{oc}=(\left|{E}_{HOMO}^{D}\right|-\left|{E}_{LUMO}^{A}\right|)-0.3.$$ (1) The major purpose of the calculation of

_V_oc is to associate HOMO of the investigated donors with LUMO of PC61BM acceptor which is a well-known acceptor having energy of HOMO = − 6.10 eV and energy of LUMO = − 3.70 eV73 and the

results obtained are represented in Table 4. As Table 4 reveals that the values of _V__oc_ for TAZD1-TAZD5 by considering the energy gap of HOMOdonor –LUMOPC61BM are found to be 1.446,

1.454, 1.454, 1.468, and 1.373 V_,_ respectively. Among all, TAZD4 shows maximum results of _V_oc. The descending order of open circuit voltage of all the studied molecules is: TAZD4 > 

TAZD2 = TAZD3 > TAZD1 > TAZD5. From literature, we have found that for a significant transference from DHOMO towards ALUMO, the LUMO of acceptor should be at lesser energy level than

that of the LUMO of donor molecules46,71. Interestingly, the LUMO of our compounds is higher than the PC61BM. These higher values of _V__oc_ elucidate the higher ICT from donor HOMO

TAZD1-TAZD5 towards PC61BM which shows highly efficient donating capability of all the studied donors as shown in Fig. 6. DENSITY OF STATES (DOS) DOS was accomplished to assist FMO analysis

and their comparative evaluation demonstrates that both of these are analogs to one another. The DOS graphs are displayed in Fig. 7. DOS are performed to disclose the dissemination of

electron density on FMOs with the analysis of percentage composition for TAZD1-TAZD5. It provides useful data related to contribution of donor as well as acceptor in the development of FMOs.

The DOS pictographs illustrate the bonding, non-bonding, and antibonding interactions amongst HOMO and LUMO74. The FMO diagrams in the Fig. 7 signify the electronic transitions that

demonstrate the intramolecular charge transfer (ICT). In DOS pictographs, the negative values characterize HOMOs while, the positively charged outcomes depict the LUMOs and the difference

among their values represents the energy gap on x-axis75. The maximum density on LUMO is noticed at − 2.5 to 4 eV in all the investigated chromophores (TAZD1-TAZD5), while on HOMO highest

density is observed from − 7 to − 12 eV as shown in Fig. 7. In TAZD2, TAZD4 and TAZD5 both HOMO and LUMO have comparable charge densities which depict their equal contribution toward FMOs.

In TAZD1-TAZD5, the donor contributes 7.7, 5.3, 4.8, 4.6 and 22.0% to HOMO, whereas to LUMO its participation is 5.5, 5.5, 5.2, 5.9 and 4.0%, respectively. In the same fashion, π-spacer

participates 72.5, 74.4, 74.8, 74.8 and 61.7% to HOMO, while 35.0, 35.2, 34.2, 35.9 and 32.6% to LUMO in TAZD1-TAZD5, respectively. Likewise, acceptor shows its percentage participation

19.8, 20.3, 20.4, 20.5 and 16.2% to HOMO in TAZD1-TAZD5, respectively, while 59.5, 59.3, 60.6, 58.2 and 63.4% to LUMO, respectively. Overall, the pattern of electronic charge distribution

elucidates the delocalization of charges and large amount of charge transfer has taken place in all the modulated chromophores. Interestingly, all the designed derivatives portray almost

alike contributions and the electron density is more prominent on the central unit (π-spacer and A units). TRANSITION DENSITY MATRIX (TDM) ANALYSIS TDM is considerably utilized for the

evaluation of electronic transitions along with their nature for TAZD1-TAZD5 in solvent phase. The study of the charge carriers localization along with delocalization and the interaction

between donor and acceptor groups followed by electron–hole delocalization as calculated by TDM analysis76. The role of hydrogen atoms has been neglected because of their small contribution.

The TDM heat maps of all the formulated molecules (TAZD1-TAZD5) are presented in Fig. S3. To study the transition of electrons within molecules in detail, we split our compound into

fragments i.e. donor (D), π-spacer and acceptor (A). It has been seen that adequate charge is transmitted out of donor towards acceptor moieties as the electron–hole pair is constituted

diagonally on the entire TDM plot and represented by clear red and green spots near the acceptor portion. The electron delocalization is seen in the diagonals of A and π-spacers and very

little in the D region. Moreover, the charge coherence and electron–hole pair generation are similarly observed in the off-diagonal portions of TDM heat maps (see Fig. S3). HOLE-ELECTRON

ANALYSIS Hole-electron analysis is popularly accomplished by utilizing the Multiwfn 3.8 software. It is a very useful method for revealing the nature of electron excitations. Moreover, it

offers a deep understanding of all different electron transfer properties77, 78. In this study, hole-electron analysis is performed at B3LYP/6-311G (d,p) to understand the charge

transmission in our studied molecules. Figure 8 shows that hole intensity is found maximum at sulphur atom (S15 and S16) of the thiophene ring of π-linker in parent compound (X94FIC) while,

the hole intensity is observed at C36 and C38 of the acceptor region. Furthermore, it is also clear from Fig. 8 that electron intensity is found at its peak at sulphur atom (S9) of the

acceptor region in compounds TAZD2, TAZD3 and TAZD4 whereas, hole intensity is observed to maximum at sulphur atoms (S15 and S16) of the π-spacer. However, in TAZD5 hole intensity is higher

at methyl group of the π-spacer and electron density is intense at nitrogen atoms (N7 and N8) of the acceptor portion. Moreover, electronic cloud is observed to be thick at nitrogen (N7 and

N8) and sulphur (S9) atoms of the acceptor in TAZD6 however, hole intensity is maximum at carbon atoms (C12 and C14) of the π-linker. The labeled structures of entitled chromophores without

hydrogen atoms are illustrated in Fig. S5. In conclusion, all the designed molecules except TAZD5, are electron type materials as electronic cloud is observed thick at electronic band in

contrast to hole intensity at hole band. In TAZD5, hole intensity is found higher at hole band therefore, it is a hole type material. EXCITON BINDING ENERGY (EB) One more consideration to

estimate the working proficiency, optoelectronic characteristics, and separation potential is binding energy (_E_b)79. The Eq. (2) is used to compute the binding energy of the studied

systems. $$E_{{{\text{b }} = }} E_{{{\text{H}} - {\text{L }} - }} E_{{{\text{opt}}}} .$$ (2) Here, _E_opt represents the least energy that is obtained when an electron moves from S0 (ground

state) to S1 (excited state) during the first electronic transition. _E_H-L signifies the energy difference among HOMO and LUMO whereas, _E_b is the binding energy that is obtained by the

difference in band gap between molecular orbitals and first singlet exciton energy. Usually, the lower the value of _E_b, greater would be the charge separation and current charge density

_J__sc_ which results in higher PCE80. The outcomes for the studied compounds calculated in acetonitrile are formulated in Table 5. According to our obtained results, the values of _E_opt

decreases progressively in all the designed compounds and is found as minimum in TAZD5 and the same behavior is observed in the HOMO and LUMO energy gap. The binding energy values in

TAZD1-TAZD5 are found to be 0.439, 0.441, 0.443, 0.441 and 0.422 eV_,_ correspondingly. The lowermost _E_b value of TAZD5 depicts that it has excessive charges that can be separated into

isolated charges. It is noted that TAZD5 exhibits high segregation of charges along with high _J_sc which indicates that it is the leading candidate to improve the efficiency of organic

photovoltaics. Furthermore, _E_b data unveil a good agreement with TDM outcomes. CHARGE TRANSFER ANALYSIS In order to understand the intermolecular charge transfer between donor and

acceptor, a complex is developed between a donor molecule (TAZD5) and acceptor (PC16BM) polymer and FMO is investigated as shown in Fig. S4. For charge transfer analysis, we selected TAZD5

due to its unique properties such as reduced band gap and greater UV–Vis absorption spectra etc. among all fabricated chromophores. According to Fig. S4, in HOMO the charge is located over

the TAZD5 donor chromophore and significantly transferred towards the acceptor polymer in LUMO which elucidates the significantly charge transfer from donor towards acceptor. CONCLUSION In a

nutshell, through the molecular engineering with azacycle donor moieties in an organic system (X94FIC) fullerene free donor based chromophores (TAZD1-TAZD5) were designed. To comprehend

their photophysical properties, the behavior of charge transfer, and structure–activity relationship, various analyses were performed at quantum chemical approach. A reasonable energy gap

between LUMO/HOMO (∆E = 2.723–2.659 eV) and significant charge transfer with wider absorption spectra (_λ_max = 554.218–543.261 nm in acetonitrile) was examined in all non-fullerene donor

chromophores. Additionally, the less binding energy outcomes (Eb = 0.422–0.411 eV) in formulated compounds specified higher rate of exciton dissociation that also reinforce the tremendous

charge transition out of HOMO towards LUMO as shown by FMOs, DOS and TDMs analyses. Moreover, the _V__oc_ values are also determined with regarding to

\({\mathrm{HOMO}}_{\mathrm{donor}}-{\mathrm{LUMO}}_{\mathrm{PC}61\mathrm{BM}}\) and interesting data was found with this order; TAZD4 (1.199 V) > TAZD2 (1.185 V) = TAZD3 (1.185 V) > 

TAZD1(1.177 V) > TAZD5(1.104 V). Consequently, significant photovoltaic materials can be developed by structural tailoring with efficient azacycle donor moieties. Moreover. this study

also encourages the experimentalist to synthesize these efficient materials for practical use. DATA AVAILABILITY All data generated or analyzed during this study are included in this

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Google Scholar  Download references ACKNOWLEDGEMENTS Dr. Muhammad Khalid gratefully acknowledges the financial support of HEC Pakistan (project no. 20-14703/NRPU/R&D/HEC/2021). Authors

are thankful for cooperation and collaboration of A.A.C.B from IQ-USP, Brazil especially for his continuous support and providing computational lab facilities. A.A.C.B. acknowledges the

financial support of the São Paulo Research Foundation (FAPESP) (Grants 2014/25770-6 and 2015/01491-3), the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) of Brazil for

academic support (Grant 309715/2017-2), and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) that partially supported this work (Finance Code 001). The authors

thank the Researchers Supporting Project number (RSP2023R29), King Saud University, Riyadh, Saudi Arabia. AUTHOR INFORMATION Author notes * These authors contributed equally: Iqra Shafiq and

Muhammad Khalid. AUTHORS AND AFFILIATIONS * Institute of Chemistry, Khwaja Fareed University of Engineering & Information Technology, Rahim Yar Khan, 64200, Pakistan Iqra Shafiq & 

Muhammad Khalid * Centre for Theoretical and Computational Research, Khwaja Fareed University of Engineering & Information Technology, Rahim Yar Khan, 64200, Pakistan Iqra Shafiq & 

Muhammad Khalid * Department of Chemistry, Division of Science and Technology, University of Education Lahore, Lahore, Pakistan Muhammad Adnan Asghar * Department of Education, Sukkur IBA

University, Sukkur, 65200, Pakistan Rabia Baby * Departamento de Qu´ımica Fundamental, Instituto de Qu´ımica, Universidade de Sao˜ Paulo, Av. Prof. Lineu Prestes, 748, Sao Paulo, 05508-000,

Brazil Ataualpa A. C. Braga * Department of Chemistry, College of Science, King Saud University, Riyadh, Saudi Arabia Saad M. Alshehri * Wellman Center for Photomedicine, Harvard Medical

School, Massachusetts General Hospital, Boston, MA, 02114, USA Sarfraz Ahmed Authors * Iqra Shafiq View author publications You can also search for this author inPubMed Google Scholar *

Muhammad Khalid View author publications You can also search for this author inPubMed Google Scholar * Muhammad Adnan Asghar View author publications You can also search for this author

inPubMed Google Scholar * Rabia Baby View author publications You can also search for this author inPubMed Google Scholar * Ataualpa A. C. Braga View author publications You can also search

for this author inPubMed Google Scholar * Saad M. Alshehri View author publications You can also search for this author inPubMed Google Scholar * Sarfraz Ahmed View author publications You

can also search for this author inPubMed Google Scholar CONTRIBUTIONS I.S.: Conceptualization; methodology. M.K.: Methodology; software; project administration. M.A.A.: Data curation; formal

analysis. R.B.: Conceptualization; methodology; software. A.A.C.B.: Conceptualization; resources. S.M.A.: Data curation; formal analysis; validation, S.A.: Data curation; formal analysis.

CORRESPONDING AUTHOR Correspondence to Muhammad Khalid. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing interests. ADDITIONAL INFORMATION PUBLISHER'S NOTE

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I., Khalid, M., Asghar, M.A. _et al._ Influence of azacycle donor moieties on the photovoltaic properties of benzo[_c_][1,2,5]thiadiazole based organic systems: a DFT study. _Sci Rep_ 13,

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