How to calculate T-T absorption energy of excited T1 state

Questions
#1

I measured TA (Transient Absorption) spectroscopy of my compound and obtained the UV-Vis absorption data of the T₁ excited state. There is a peak that I suspect corresponds to a triplet–triplet absorption (T₁ → Tₙ transition), and I would like to confirm whether this peak indeed arises from a T–T absorption using Q-Chem calculations. Is there a way to do this?

#2

Such calculations are possible with Q-Chem with a few methods—please refer to the Q-Chem User Manual (7.1.1 Overview‣ 7.1 General Excited-State Features ‣ Chapter 7 Open-Shell and Excited-State Methods ‣ Q-Chem 6.3 User’s Manual). If you have already tried such a calculation with Q-Chem and your method of choice but have further questions, please tell us how you are setting up the Q-Chem calculation by posting a sample input using the preformatted text icon “</>”.

#3

I have already optimized the T₁ state of my complex using the input file below. Now, I would like to calculate the triplet–triplet (T–T) absorption energy and strength.


$rem
Job_type opt
Method B3LYP
Basis def2-SVP
DFT_D D3_BJ
Symmetry False
Max_SCF_cycles 3000
Geom_opt_max_cycles 3000
mem_total 2000000
mem_static 2000
CIS_N_Roots 20
CIS_Singlets False
CIS_Triplets True
Set_state_deriv 1
Max_CIS_cycles 3000
THRESH 14
GEOM_OPT_TOL_GRADIENT 100
GEOM_OPT_TOL_DISPLACEMENT 400
GEOM_OPT_TOL_ENERGY 33
XC_GRID 3
$end

@@@

$molecule
read
$end

$rem
Job_type freq
Method B3LYP
Basis def2-SVP
DFT_D D3_BJ
Symmetry False
Max_SCF_cycles 3000
mem_total 1000000
mem_static 2000
CIS_N_Roots 20
CIS_Singlets False
CIS_Triplets True
Set_State_Deriv 1
CPSCF_NSEG 2
$end
@@@

$molecule
read
$end

$rem
Job_type sp
Method B3LYP
Basis def2-TZVP
DFT_D D3_BJ
Solvent_method SMD
Symmetry False
Max_SCF_cycles 300
mem_total 200000
mem_static 4000
CIS_N_Roots 40
CIS_Singlets True
CIS_Triplets True
Max_CIS_cycles 300
Print_Orbitals True
Molden_Format True
State_Analysis True
CIS_Ampl_Anal True
CHELPG True
$end

$smx
Solvent THF
$end