Structural Insight and Ultrafast Dynamics of 2D-Porphyrin

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C: Physical Processes in Nanomaterials and Nanostructures

Structural Insight and Ultrafast Dynamics of 2D-Porphyrin Nanostructures Rajesh Bera, Sandipan Chakraborty, Sandip Kumar Nayak, Biman Jana, and Amitava Patra J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b03112 • Publication Date (Web): 30 May 2019 Downloaded from http://pubs.acs.org on May 30, 2019

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The Journal of Physical Chemistry

Structural Insight and Ultrafast Dynamics of 2D-Porphyrin Nanostructures

Rajesh Bera†, Sandipan Chakraborty§, S. K. Nayak‡, Biman Jana§ and Amitava Patra†* †School of Materials Sciences, Indian Association for the Cultivation of Science, Kolkata 700032, India §School of Chemical Sciences, Indian Association for the Cultivation of Science, Kolkata 700032, India ‡Bio-Organic

Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India

*To whom correspondence should be addressed. E-mail: [email protected] Phone: (91)-33-2473-4971, Fax: (91)-33-2473-2805

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The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT

Two dimensional (2D) nanostructures are an emerging class of materials for designing artificial light harvesting system because of their unprecedented electronic properties. Here, we design 2D nano-assembly of 5,10,15,20-tetra (4-dodecyloxyphenyl) porphyrin by changing solvent polarity. We provide molecular dynamics simulation data to understand the internal structure of the 2D porphyrin nanostructures and study their exciton dynamics by femtosecond transient absorption spectroscopy. We find that porphyrins incline to stack on each other in parallel-displaced manner which results in formation of right-handed helix within the nano-assembly. Long alkyl side-chains tightly wrap around each other to reduce the hydrophobic solvent accessible surface area, results in the formation of 2D nanodisk structure where the central porphyrin moieties exist as disjoined helices. Ultrafast spectroscopic study of 2D porphyrin aggregate exhibits very fast internal conversion process from S2 → S1 transition in ~100 fs time scale along with direct S2 →S0 transition in 350 fs. The vibrational cooling and relaxation process (inside S1 manifold) is found to be decreased from 10 ps (monomer) to 5 ps (aggregated structure). It is evident that the probability of intersystem crossing (ISC) from S1 (or S2) to T1 state is greatly reduced due to aggregation. Analysis reveals that the fabrication of 2D porphyrin structures and study of excited state dynamic would be paved in designing and mimicking the organic based artificial light harvesting system.


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1. INTRODUCTION Significant attention has been given on designing nanostructures for efficient light harvesting applications such as photocatalysis, water splitting and solar cell.1-8 Recently, the assembled structure of organic molecules has been studied extensively due to their strong intermolecular π electronic coupling between coherently aligned chromophores which increases the delocalization of electron to a great extent.9-12 Among them, assembled structure of porphyrin is of potential interest for efficient light harvesting applications because of its high absorption coefficient, exciton generation and efficient charge transfer process.13-16 Generally aggregation of macromolecules occurs in two types i.e. J-type and H-type.17-18 Jtype aggregated structure is formed when molecules are aggregated by edge to edge arrangements (red shifted absorption band) whereas H-type aggregation occurs due to face to face arrangements (blue shifted absorption band). It is obvious that J-type aggregation of porphyrin could be mimicking the chlorophyll in natural photosynthesis.Thus, the aggregated structures of porphyrin are found to be a potential candidate in mimicking the natural light harvesting system. The designing and applications of porphyrin nano rod, wire, tube and spherical structure are evident for solar energy conversion.16-19 Hasobe reported an overview on solar energy conversion based on porphyrin supramolecular architectures.20 Fan and his co-worker have synthesized nano-octahedra and wire like porphyrin nanostructures and studied their photocatalysis efficiency.21 The photocatalytic activity of one dimensional porphyrin nanorod is compared with other shapes of porphyrin nanostructures.22 Hybrid structures of well aggregated porphyrin and graphene also studied extensively for light harvesting systems. Liu et al. have investigated photocatalytic performance of the composite of one dimensional porphyrin rod and graphene composite.23 Graphene/porphyrin nanostructures are found to be potential for efficient light harvesting systems.24-25 Most of the studies are restricted in spherical, tube or rod shaped porphyrin structures. Less emphasis is given on designing two dimensional (2D) porphyrin nanostructures which could be beneficial for constructing an efficient light harvesting system because of unique physicochemical and optical properties. Several studies based on porphyrin monomer are reported in literature. Zewail et al. have investigated ultrafast relaxation dynamics of free base porphyrin by using femtosecond fluorescence and transient absorption spectroscopy.26 Enescu et al. also have studied the relaxation process from upper excited states of H2TMPyP porphyrin by transient absorption spectroscopy in femtosecond time scale.27 Salvi et al. have studied the excited state dynamics of porphyrin and compared the experimental results with theoretical calculations.28 Majority 3 ACS Paragon Plus Environment


of the research interest is directed towards the spectroscopic investigation of porphyrin monomer. Energy relaxation process of porphyrin is modified in aggregated structures because of several nonradiative processes. Therefore, it is very important to study the relaxation dynamics of the aggregated porphyrin molecules by using ultrafast spectroscopy to unveil the total relaxation pathways of porphyrin aggregate which will help to design the efficient artificial light harvesting system. In earlier, Kobayashi et al. have reported the ultrafast dynamics of S1 and S2 exciton in one dimensional J-aggregated structure of porphyrin by femtosecond pump-probe system.29-30 Collini et al. have reported transient absorption and two photon absorption spectra of monomeric and aggregated state of water soluble H4TPPS2- porphyrin.31 The excited state dynamics of nano-aggregates of zincphthalocyanine is studied by Palit and his co-worker.32 On the other hand, Wan et al. studied optical properties of the Frenkel excitons in self-assembled porphyrin tubular aggregates and they reported both linear and non linear exciton absorption, relaxation pathways, by using ultrafast spectroscopy and stochastic exciton theoretical model.33 To our knowledge, less attention has been given on designing of 2D porphyrin aggregate and understanding the exciton dynamics by ultrafast spectroscopy. Here, we describe the formation of the 2D porphyrin aggregates by using 5,10,15,20tetra(4-dodecyloxyphenyl) porphyrin (Scheme 1). Meso-tetrakis (4-dodecenyloxyphenyl) porphyrin has four long aliphatic chains at the outer core of porphyrin which is highly soluble in organic solvent (in tetrahydrofuran). We prepared aggregated porphyrin nanostructure by mixing a certain percentage of water. Molecular level characterizations of the 2D nanoassembly have been carried out by using FE-SEM, AFM, and circular dichroism spectroscopy in addition with molecular dynamics simulation. Detailed structural characterizations have been carried out using equilibrium molecular dynamics simulation. The exciton dynamics of 2D structures of porphyrin are studied by using transient femtosecond spectroscopy and compare them with the monomer of porphyrin. The present study reveals that excitons transfer from singlet excited state to triplet state in porphyrin monomer whereas the probability of singlet to triplet transfer is reduced to a great extent in case of 2D aggregated structure. Analysis reveals that relaxation processes are strongly influenced by the 2D aggregates which could be beneficial for developing efficient light harvesting system.


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2. EXPERIMENTAL SECTION 2.1. Materials and Reagents. Tetrahydrofuran (THF), de-ionised water, propionic acid were purchased from Merck. 4-(dodecyloxy)benzaldehyde, pyrrole were purchased from Sigma Aldrich and has been used without further purification. 2.2. Synthesis of 5,10,15,20-tetra(4-dodecyloxyphenyl)porphyrin(4-dpPOR). To a refluxing solution of 4-(dodecyloxy)benzaldehyde (10 g, 34.5 mmol) in propionic acid (200 ml), a solution of pyrrole (2.31 g, 34.5 mmol) in propionic acid (50 ml) was added drop wise under vigorous stirring. The brown solution was then refluxed for 1 h and cooled to ambient temperature. The black precipitate thus obtained was collected and washed with methanol to get a purple colored solid. The solid was purified by silica gel column chromatography using dichloromethane-hexane as eluent to furnish 5,10,15,20-tetra(4-dodecyloxyphenyl)porphyrin as purple crystals (1.04 g, 8.9% ). The schematic representation is given below (scheme 1). 1H NMR (CDCl3, 200 MHz): δ 8.87 (s, 8H, pyrrole β-H), 8.10 (d, J = 8.6 Hz, 8H, Ar-H), 7.27 (d, J = 8.4 Hz, 8H, Ar-H), 4.25 (t, J = 6.4 Hz, 8H, OCH2), 1.92-2.02 (m, 8H), 1.32-1.63 (m, 72H), 0.91 (t, J = 6.3 Hz, 12H), -2.73 (bs, 2H, NH).(Figure S1). OC12H25

C12H25O CHO

N H

propionic acid

+

N

N

reflux

N H

H N

OC12H25

C12H25O

OC12H25

Scheme1. Schematic representation of synthesis of 5,10,15,20-tetra (4-dodecyloxyphenyl) porphyrin (4-dpPOR). 2.3. Preparation of 2D nanostructures. The two dimensional (2D) nanostructures were designed by varying solvent polarity. First, we have prepared 2 mL stock solution of 4dpPOR having 1mM concentrations in dry THF solution. Then we have taken 95% (v/v) volume ratio of water and THF in a glass vial and mixed 0.2 mL of 4-dpPOR stock solution at a time. This glass vial was kept in a dark place without disturbing for 1 hour. After that we took the solution out and elucidated the all morphological and spectroscopic characterization accordingly. 5 ACS Paragon Plus Environment


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2.4. Characterization. Field emission scanning electron microscopic (FE-SEM, JEOL, JSM6700F) study was carried out for morphological characterization of 4-dpPOR nanostructures. Room temperature optical absorption spectra were taken by a UV-vis spectrophotometer (SHIMADZU). Room temperature photoluminescence spectra were recorded by a Fluoromax-P (HORIBA JOBIN YVON) photoluminescence spectrophotometer. Circular dichroism (CD) spectra were taken by JASCO (J-815-150S) instrument. For the time correlated single photon counting (TCSPC) measurements, the samples were excited at 405 nm using a pico-second diode laser (IBH Nanoled-07) in an IBH Fluorocube apparatus. The repetition rate was 1 MHz. The fluorescence decays were analyzed using IBH DAS6 software. The following equation was used to analyze the experimental time resolved fluorescence decays, P(t ) : n

P(t )  b   i exp( i

t

i

)

(1)

Here, n is the number of discrete emissive species, b is a baseline correction (“dc” offset), and αi and τi are the pre-exponential factors and excited-state fluorescence lifetimes associated with the ith component, respectively. For multi-exponential decays the average lifetime,, was calculated from the following equation: n

     i i

(2)

i 1

Where  i   i /   i and it is the contribution of the decay component. αi and τi are the preexponential factors and excited-state fluorescence lifetimes associated with the ith component, respectively. This value should be called an amplitude-weighted lifetime. The investigation of ultrafast spectroscopy was done using the similar Femtosecond fluorescence upconversion spectrophotometer with a Halcyone ultrafast setup (coherent) which was reported elsewhere.34 The sample was excited with 400 nm wavelength of excitation, pumped using a 800 nm femtosecond (fs) (140fs pulse width, 80 MHz repetition rate) laser pulse (4.4 W) from a Ti:sapphire oscillator (Chameleon,Coherent) coupled to a second harmonic generator (by BBO type I crystal). The emission wavelength (657-650 nm) and the gate pulse of the fundamental beam (800 nm) were upconverted using a nonlinear crystal (BBO type II). The FWHM of the instrument response function was about 300 fs. The femtosecond time resolved decay data were fitted using Surface Xplorer 2.3 fitting software. The same femtosecond transient absorption spectrophotometer (TAS) setup, reported elsewhere was used here.35 6 ACS Paragon Plus Environment

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Briefly, a mode-locked Ti:sapphire oscillator (Seed laser, Mai-Tai HP, Spectra Physics) generated pulses of ~80 fs duration at 800 nm, and repetition rate of 80 MHz. A separate pump laser (Nd:YLF laser, 527 nm, ASCEND EX, Spectra-Physics) required for amplifying the seed pulse. The output from the amplifier was (800 nm, ~100fs, 1 KHz, pulse energy 5mJ) send to spectrophotometer. BBO crystal was used to generate 400 nm pump beam for exciting the samples. The other part of the 800 nm light was focused on a CaF2 plate to generate a white-light continuum (WLC) and used as probe pulse. The WLC was also divided into two parts; one part was used as probe pulse and the other one as reference. The reference and transmitted probe beam were then sent to different diode arrays where reference beam helps to account for the intensity fluctuation in white light continuum. The power of pump pulse (2 ns are observed. Here, we have excited the S2 or soret band of porphyrin and monitored the emission of the Qx (0,0) band. Therefore, the observed rise time (19.5 ps) of the monomer porphyrin is attributed due to indirect population of Qx state. This is followed by vibrational cooling through the internal conversion (IC) process or relaxation of excess energy within solvent molecule. It is interesting to notice that the aggregated structure of porphyrin have three time constants where one rise component of 5 ps and other two decay components are of 10 ps and 300 ps. After the aggregation, the rise time is reduced from 19 ps to 5 ps, indicating the faster population in the S1 state due to aggregation.

Normalized Counts

1.5

1.0

(a)

0.5

(b) 0.0

0

50

100

150

200

Delay Time (ps)

Figure 8. Femtosecond fluorescence upconversion decay curves of 4-dpPOR monomer (a), and 2D aggregated structure (b). (λex: 400 nm)

(B)

(A)

0.03

0.00

0.02 0.5 ps 1 ps 10 ps 100 ps 500 ps 1 ns 2 ns

-0.03

0.01 OD

OD

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


420 nm 443 nm 496 nm 535 nm 574 nm 626 nm 690 nm

-0.05

-0.06

-0.06

420

490

560

630

0

700

2

4

6

8

Delay Time (ps)

Wavelength (nm)


100

200


Figure 9. (A) Transient absorption spectra of 4-dpPOR monomer at different delay times. (B) Kinetics at different probe wavelengths (420 nm, 443 nm, 496 nm, 535 nm, 580 nm, 626 nm, and 690 nm). Femto-second transient absorption spectroscopic study is performed to understand the exciton dynamics of both 4-dpPOR monomer and 2D aggregate structures. Both the monomer and 2D aggregate structures were excited at their soret band at 400 nm. In figure 9A, the TA spectrum of monomeric porphyrin shows a broad positive transient absorption throughout the whole spectral region due to excited singlet state absorption (ESA) band and the negative absorption is due to the bleaching of the soret and Q bands at different time delays which is consistent with previous results.55 Figure 9B depicts the temporal profile of the transient signal of the GSB at 420 nm, and excited state absorption (ESA) from the non relaxed excited state at different wavelengths like 443 nm, 496 nm, 535 nm, 574 nm, 626 nm and 690 nm. These time evolutions consist of several processes such as GSB, stimulated emission (SE), excited state absorption (ESA) from S1 to Sn or S2 to Sn states. Here, all the time profiles were fitted by four exponential function at their corresponding wavelength to obtain all the kinetic parameters more precisely, keeping the fixed time constants of each probe wavelength such as τ1= 0.25-0.35 ps, τ2= 2 ps, τ3= 10 ps and τ4= >10 ns and the amplitudes of corresponding time constants are allowed to vary (Table 1). The fast decay component (τ1) of about 0.25-0.35 ps is due to the S2→S1 internal conversion (IC) in porphyrins. Gellini et al. have reported that the ultra fast internal conversion process occurs in the 10 ns) A4

420 (GSB)

τ1a (0.250.35ps) A1 (-) 0.03

(-) 0.09

(-) 0.02

(-) 0.85

443 (ESA)

-1

0.19

0.24

0.54

494 (ESA)

-0.97

0.62

-0.03

0.38

535 (ESA)

-0.91

0.47

-0.09

0.53

580 (ESA)

(-) 0.96

0.67

(-) 0.04

0.33

627 (ESA)

(-) 0.93

0.26

(-) 0.07

0.74

690 (ESA)

(-) 0.99

0.23

(-) 0.01

0.77

Wavelength (nm)

monomer

a±5

%(error). (-) sign indicates the growth time constant when it is ESA.



IC 0.25-0.35 ps

S2

VR 1.8 ps VC 10 ps

ISC >10 ns

S1

T1

0.25 ps ~10 ns

>10 ns

S0 Scheme2. Probable relaxation pathways of 4-dpPOR monomer after soret band excitation at 400 nm.

(B)

0.005

(A) 0.00

80 fs 100 fs 20 ps 50 ps 80 ps 100 ps 300 ps

-0.01

-0.02

500

600

OD

0.000 OD

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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-0.008

442 nm 468 nm 496 nm 516 nm 572 nm 626 nm 695 nm

-0.016 -0.024 -0.032

700

0

Wavelength (nm)

50

100

150

200

Delay Time (ps)

Figure 10. (A) Transient absorption spectra of 2D 4-dpPOR aggregate at different delays times. (B) Kinetics at different wavelengths (442 nm, 468 nm, 496 nm, 518 nm, 572 nm, 626, and 695 nm. Now, we have measured the transient spectra of the 2D aggregated porphyrin nanostructures. Figure 10A shows the TA spectra of 2D 4-dpPOR aggregates at different delayed time scales. Interestingly, we observed a strong bleaching at 442 nm wavelength due to the soret band which is consistent with absorption spectrum (Figure 2a). Fast recovery of 22 ACS Paragon Plus Environment

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this band within 100-200 ps time scale is due to nonradiative pathways of aggregated structure. After excitation, the excitons would be promoted from ground state to lowest excitonic state of S2 manifold and then subsequently to the other excitonic states. It is noticed that the bleaching of soret band (Bx) at 442 nm probe wavelength is dominated in the whole spectra. Again, we have taken five time constants such as τ1 =0.1 ps, τ2 =0.2 ps, τ3 =0.35 ps, τ4 =5 ps and τ5= >200 ps to fit the data at different probe wavelengths (Figure 10B) and the amplitudes are allowed to vary (Table 2). We observed very faster time constant τ1=0.1 ps with significant contribution in temporal profile compare to 4-dpPOR monomer (0.25-0.35 ps) and it can be attributed to the internal conversion from S2 manifold to S1 manifold of 4dpPOR aggregates. Earlier, Collini et al. have predicted 0.3 ps time for IC process from S2 to S1 manifold band of J-aggregated H4TPPS2- porphyrin.31 This is because of reduction of energy gap between S2 and S1 manifold due to aggregation as a result the faster exciton transfer occurs and quickly populate the hot vibronic state of S1 manifold band. The growth time (0.2 ps) in the bleaching kinetics at 442 nm indicates the vibration relaxation of S2 state. It is to be noted that this growth time is absent in case of 4-dpPOR monomer (Table 2). The time constant 0.35 ps (τ3) in temporal profile is assigned as the S2→S0 recombination time because this type of aggregation allowed the direct transition from S2 excitonic state to S0 state. The decay component 0.35 ps at 442 nm wavelength and the growth component at 468 nm probe wavelength are observed and it is consistent with previous results.30, 55 Analysis suggests that the 0.35 ps is correlated with the S2 fluorescence of aggregated 4-dpPOR structure whereas 0.25 ps time scale is attributed S2→S0 recombination in case of 4-dpPOR monomer. It is reflected from TA experiment that the S2 fluorescence intensity increases in 2D aggregated structure than monomeric 4-dpPOR. Kobayashi et al. have reported that S2→S0 recombination in case of porphyrin J-aggregated structure occurs in the time scale of 0.3 ps. However, the 0.35 ps (τ3) time scale is absent for other probe wavelength in kinetic profile which reveals that the fluorescence comes from S2 state. However, after IC process the hot S1 exciton can be relaxed through the several processes. In general for the large molecules in solution, vibrationally excited excitons are redistributed in the intramolecular vibrational energy level to achieve thermal equilibrium. In aggregated structure, the intra aggregate vibrational energy redistribution (IAVR) is expected to be completed in few femtosecond time scales (~100 fs). With the IAVR process, the vibrational cooling (VC) of excited molecules is also expected to cool down the hot excitons by interacting with solvent molecules. The time constant τ4 (5 ps) is reasonably attributed due to intra aggregated and aggregate-solvent vibrational energy redistribution whereas vibrational cooling occurs in 10 23 ACS Paragon Plus Environment


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ps in monomeric 4-dpPOR. This result nicely corroborate with the previous report by Kano and his co-worker where S1 exciton is cooled down through vibrational cooling and phase space cooling process within 4-10 ps time scale.30 Finally another comparatively long component (τ5) of 100-200 ps signifies the relaxation of S1 excitons to ground state (S0) whereas very large time scale (> 10 ns) is found for recovery of excited excitons in case of porphyrin monomer. It is noteworthy that the probability of intersystem crossing from S1 to T1 state is significantly reduced in case of 2D aggregated structure compare to 4-dpPOR monomer. Based on the kinetic parameters and the literature value we have proposed relaxation pathways of exciton in 2D aggregated structure (Scheme 3). This type of self assemble structure leads a bridge between several chromophore units which further accelerate the exciton transfer process during photo excitation via non radiative process. Table 2. Kinetic parameters of the fitted data of the 2D 4-dpPOR aggregated structure (nm)

τ1b (0.1 ps) A1

442(GSB)

-0.46

τ2b (0.2 ps) A2 1

468 (ESA)

-0.93

0.74

-0.07

0.15

0.11

496 (ESA)

-1

0.7

-

0.18

0.12

518 (GSB)

-0.93

1

-

-0.02

-0.05

572 (ESA)

-1

0.53

-

0.27

0.2

626 (ESA)

-1

0.11

0.56

0.33

695 (ESA)

-1

0.86

0.09

0.05

Wavelength

2D porphyrin

b±5

τ3b (0.35 ps) A3 -0.43

τ4b (5 ps) A4 -0.06

τ5b (>200 ps) A5 -0.05

-

% (error). (-) sign indicates the growth time constant when it is ESA.


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S2 manifold 0.2 ps IC 0.1 ps S1 manifold 5ps

0.35ps

>200 ps

S0 Scheme3. Probable relaxation pathways of aggregated 2D structure after soret band excitation at 400 nm. 4. CONCLUSIONS In summary, we have designed 2D nanostructures of free base porphyrin by solvent variation and these 2D nanostructures were characterized by SEM and AFM studies. Molecular dynamics simulation was used to understand the structure of 2D self-assembled nano-disk of 4-dpPOR. Parallel-displaced π-π stacking interactions occur for obtaining nanoscale supra-molecular assemblies 2D aggregated structure. Size and shape of the porphyrin based self-assembly can be tuned by changing the associated alkyl chain lengths. The excited state relaxation dynamics of 2D nanostructures and monomeric porphyrin are investigated by femtosecond up conversion and transient absorption spectroscopy. The analysis reveals that the exciton relaxation and recombination processes of 2D nanostructure of porphyrin are different from monomeric state due to change in inter molecular coupling between molecules in aggregated form which accelerates exciton mobility. This type of aggregation may be mimicking the natural light harvesting antenna material and it can be used in fabricating artificial light harvesting system. ASSOCIATED CONTENT Supporting Information NMR of 5,10,15,20-tetra(4-dodecyloxyphenyl)porphyrin and PL spectra of monomer and 2D aggregated structure in addition to the initial structure of monomeric and stacked 25 ACS Paragon Plus Environment


porphyrin derivatives. UV-visible, PL, SEM, and AFM data after adding 12% and 50% water in THF solution of porphyrin. XRD pattern of 2D aggregated porphyrin. The Supporting Information is available free of charge on the ACS Publications website. ACKNOWLEDGMENTS DST-TRC project is gratefully acknowledged for the financial support. RB and SC thanks to IACS for fellowship. BJ gratefully acknowledges financial support from the Department of Science and Technology SERB grant (EMR/2016/001333).


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“TOC Graphic” S2 manifold 0.2 ps

IC 0.1 ps S1 manifold 5ps

0.35ps

>200 ps 1 µm

S0


Structural Insight and Ultrafast Dynamics of 2D-Porphyrin

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