Excited-state double proton transfer(ESDPT)is a controversial issue which has long been plagued with theoretical and experimental communities.Herein,we took 1,8-dihydroxy-2-naphthaldehyde(DHNA)as a prototype and used combined complete active space self-consistent field(CASSCF)and multi-state complete active-space second-order perturba-tion(MS-CASPT2)methods to investigate ES-DPT and excited-state deactivation pathways of DHNA.Three different tautomer minima of S1-ENOL,S1-KETO-1,and S1-KETO-2 and two crucial conical intersections of S1S0-KETO-1 and S1S0-KETO-2 in and between the S0 and S1 states were obtained.S1-KETO-1 and S1-KETO-2 should take responsibility for ex-perimentally observing dual-emission bands.In addition,two-dimensional potential energy surfaces(2D-PESs)and linear interpolated internal coordinate paths connecting relevant structures were calculated at the MS-CASPT2//CASSCF level and confirmed a stepwise ESDPT mechanism.Specifically,the first proton transfer from S1-ENOL to S1-KETO-1 is barrierless,whereas the second one from S1-KETO-1 to S1-KETO-2 demands a barrier of ca.6.0 kcal/mol.The linear interpolated internal coordinate path connecting S1-KETO-1(S1-KETO-2)and S1S0-KETO-1(S1S0-KETO-2)is uphill with a barrier of ca.12.0 kcal/mol,which will trap DHNA in the S1 state while therefore enabling dual-emission bands.On the other hand,the S1/S0 conical intersections would also prompt the S1 system to decay to the S0 state,which could be to certain extent suppressed by locking the rotation of the C5-C8-C9-O10 dihedral angle.These mechanistic insights are not only helpful for un-derstanding ESDPT but also useful for designing novel molecular materials with excellent photoluminescent performances.

Bin-Bin Xie;Ke-Xin Wang;Pei-Ke Jia;Xiang-Yang Liu;Ganglong Cui

Hangzhou Institute of Advanced Studies,Zhejiang Normal University,Hangzhou 311231,China;College of Chemistry and Material Science,Sichuan Normal University,Chengdu 610068,China;Key Laboratory of Theoretical and Computational Photochemistry,Ministry of Education College of Chemistry,Beijing Normal University,Beijing 100875,China

化学物理学报（英文版）

[1]Bin-Bin Xie;Ke-Xin Wang;Pei-Ke Jia;Xiang-Yang Liu;Ganglong Cui-.Excited-State Double Proton Transfer of 1,8-Dihydroxy-2-Naphthaldehyde:a MS-CASPT2//CASSCF Studyt)[J].化学物理学报（英文版）,2022(03):422-430

Dihydroxy,Naphthaldehyde,CASPT2,Studyt,ESDPT,naphthaldehyde,DHNA,tautomer,ENOL,KETO,S1S0,PESs,barrierless,O10

Excited,State,Double,Proton,Transfer,CASSCF,double,proton,transfer,controversial,issue,which,has,long,been,plagued,theoretical,experimental,communities,Herein,took,dihydroxy,prototype,used,combined,complete,active,space,self,consistent,field,multi,second,order,perturba,methods,investigate,excited,deactivation,pathways,Three,different,minima,two,crucial,conical,intersections,between,states,were,obtained,should,take,responsibility,perimentally,observing,dual,emission,bands,In,addition,dimensional,potential,energy,surfaces,2D,linear,interpolated,internal,coordinate,paths,connecting,relevant,structures,calculated,level,confirmed,stepwise,mechanism,Specifically,first,from,whereas,one,demands,kcal,uphill,will,trap,while,therefore,enabling,On,other,hand,would,also,prompt,system,decay,could,certain,extent,suppressed,by,locking,rotation,C5,C8,C9,dihedral,angle,These,mechanistic,insights,are,not,only,helpful,derstanding,but,useful,designing,novel,molecular,materials,excellent,photoluminescent,performances

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